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A friend has spent the last three years hounding me about seed oils. Every time I thought I was safe, he’d wait a couple months and renew his attack:

“When are you going to write about seed oils?”

“Did you know that seed oils are why there’s so much {obesity, heart disease, diabetes, inflammation, cancer, dementia}?”

“Why did you write about {meth, the death penalty, consciousness, nukes, ethylene, abortion, AI, aliens, colonoscopies, Tunnel Man, Bourdieu, Assange} when you could have written about seed oils?”

“Isn’t it time to quit your silly navel-gazing and use your weird obsessive personality to make a dent in the world—by writing about seed oils?”

He’d often send screenshots of people reminding each other that Corn Oil is Murder and that it’s critical that we overturn our lives to eliminate soybean/canola/sunflower/peanut oil and replace them with butter/lard/coconut/avocado/palm oil.

This confused me, because on my internet, no one cares. Few have heard of these theories and those that have mostly think they’re kooky. When I looked for evidence that seed oils were bad, I’d find people with long lists of papers. Those papers each seemed vaguely concerning, but I couldn’t find any “reputable” sources that said seed oils were bad. This made it hard for me to take the idea seriously.

But my friend kept asking. He even brought up the idea of paying me, before recoiling in horror at my suggested rate. But now I appear to be writing about seed oils for free. So I guess that works?

On seed oil theory

There is no one seed oil theory.

I can’t emphasize this enough: There is no clear “best” argument for why seed oils are supposed to be bad. This stuff is coming from internet randos (♡) who differ both in what they think is true, and why they think it. But we can examine some common arguments.

We ate seed oil and we got fat.

One argument is that for most of human history, nobody dieted and everyone was lean. But some time after the industrial revolution, people in Western countries started gaining weight and things have accelerated ever since. Here’s BMI at age 50 for white, high-school educated American men born in various years:

For the last few decades, obesity (BMI ≥30) has grown at around 0.6% per year. Clearly we are doing something wrong. We evolved to effortlessly stay at a healthy weight, but we’ve somehow broken our regulatory mechanisms. Anywhere people adopt a Western diet, the same thing happens.

Of course, the Western diet is many things. But if you start reading ingredients lists, you’ll soon notice that everything has vegetable oil in it. Anything fried, obviously, but also instant noodles, chips, crackers, tortillas, cereal, energy bars, canned tuna, processed meats, plant-based meat, coffee creamer, broths, frozen dinners, salad dressing, and sauces. Also: Baby food, infant formula, and sometimes even ice cream or bread. People eat a lot more vegetable oil than they used to (figure from Lee et al. (2022)):


Many vegetable oils (and particularly seed oils) are high in linoleic acid. And guess what’s making up a rapidly increasing fraction of body fat? (figure from Stephan Guyenet):

Even many types of meat now have high linoleic acid levels, because the animals are now eating so much vegetable oil. It’s plausible this is doing something to us.

And seed oils are highly processed.

Another common argument is that even if we can’t identify exactly where the Western diet went wrong, we know that we spent almost our whole evolutionary history eating like hunter-gatherers (and most of the rest eating like subsistence farmers). And hunter-gatherers are all thin. So maybe we should eat like they did?

That sounds kind of fanciful, but consider the most conventional dietary advice, the thing that every expert screams every time they have a chance—AVOID PROCESSED FOOD.

The USDA defines processing as:

washing, cleaning, milling, cutting, chopping, heating, pasteurizing, blanching, cooking, canning, freezing, drying, dehydrating, mixing, or other procedures that alter the food from its natural state. This may include the addition of other ingredients to the food, such as preservatives, flavors, nutrients and other food additives or substances approved for use in food products, such as salt, sugars and fats.

Basically, don’t do… anything? That sounds awfully similar to eating like a hunter-gatherer. It’s unclear why many of these types of processing would be harmful. (Cooking? Washing?) But maybe that’s smart—maybe biology and nutrition are so complicated that we shouldn’t even try to understand them.

Traditional oils involve some processing, but they’re pretty easy. To make butter, you milk a cow and churn the milk. To make olive oil, you grind some olives and press them. To make lard, you take a beautiful pig with hopes and dreams, you kill it, you cut off the fattiest bits, and then you boil them and strain.

But here’s how you make canola oil: Take rapeseeds, put them through a vibrating sieve, then a roller mill, then a screw press, then do a hexane extraction, then do a sodium hydroxide wash in a centrifuge, then cool and filter out wax, then pass through bleaching clay, then do a steam injection in a vacuum. Whatever comes out of this is not something your DNA anticipates.

And some studies say seed oils are bad.

Another argument is that seed oils are bad experimentally. Even if you don’t understand how nutrition works, you can still try stuff—e.g. you can have people replace animal fat (or saturated fat) with vegetable oil (or unsaturated fat) and see if this makes them healthier. Usually, such trials were done with the expectation that they’d show vegetable oils were healthier. And often they do. But in a couple cases—notably the Sydney Diet Heart Study, and the Minnesota Coronary Survey—the groups with more vegetable oil did worse, not better.

And there are plausible mechanisms.

Our last argument is that we know how seed oils hurt you. People seem to suggest five possible mechanisms:

  1. Maybe linoleic acid (common in seed oils) is metabolized into arachidonic acid, and thereby causes inflammation.
  2. Maybe linoleic acid becomes oxidized LDL and thereby causes inflammation.
  3. Maybe it’s the ratio of omega-6 to omega-3 fats you eat that matters.
  4. Maybe vegetable oil doesn’t make you feel full like animal fats do, meaning vegetable oils lead to overeating.
  5. Maybe vegetable oils have an increased propensity to become trans fats.

On fat

There are many kinds of fat.

When first trying to make sense of these arguments, I encountered terms like “cis medium-chain omega-7 polyunsaturated fat”, which left me confused and terrified. (Biochemistry’s enormity has always had a way of making me feel insignificant.) After looking into things, I’m still quite scared, but at least I’ve made the Dynomight Fatty Acid Classifier.

Fat is made of fatty acids—chains of carbon atoms linked via hydrogen bonds. Usually, these are “single” bonds. But sometimes there are “double” bonds, which are very important because they are easier to break apart. So different fatty acids are categorized mostly based on the double bonds. So, behold:

If you want, you can further divide things up in terms of the length of the fatty acid, or even count how many single bonds there are between each double bond.

Different oils have different fats.

Here’s a picture (simplified from Mikael Häggström’s version):

Animal fat tends to be high in saturated and monounsaturated fat while vegetable oil tends to be high in polyunsaturated fat. But there are a few notable exceptions (not all listed above):

  • Olive oil, canola oil, and avocado oil are high in monounsaturated fat.
  • Coconut oil is high in saturated fat.
  • Palm oil has both saturated and monounsaturated fat, but little polyunsaturated fat.

Of course, you can also break things down into different subcategories of fats or even individual fatty acids.

Trans fat is bad.

The double bonds in fatty acids have two possible configurations. They can be “normal” (cis) or they can be “reversed” in a way that leaves the rest of the fatty acid chain “flipped” (trans). (The Dynomight Biologist howls in protest at this description, but is overruled.)

Starting around 100 years ago, people noticed you could “hydrogenate” unsaturated fats by heating them and cramming in extra hydrogen atoms. If this is done completely, it will transform all the double bonds into single bonds, changing the unsaturated fat into saturated fat. This gives something similar to lard, but cheaper. You probably eat hydrogenated vegetable oils all the time—they’re used for “shortening” and are in icing and all sorts of baked and fried foods.

But if you don’t fully hydrogenate the oil you end up with—you guessed it—partially hydrogenated oil, in which many of the natural cis bonds will be converted to trans bonds. Partially hydrogenated oils are cheap, have high shelf lives, and can easily be made in a range of consistencies.

That’s a shame because trans fats are pretty rare in nature (maybe 3% of butter/canola oil, around 0.5% of olive oil) and evolution doesn’t seem to have prepared us to eat large amounts of them. The WHO calls them “deadly”. It’s consensus that they cause obesity, diabetes, and heart disease, though the mechanism of harm often still isn’t understood. Trans fats started being phased out around the world about 25 years ago. But before that happened, they were estimated to cause 30k to 100k deaths per year in the United States.

So, don’t eat trans fats.

About that, bad news—if you cook with unsaturated fat at high temperature you can make your own trans fats right in your kitchen. Though it seems like not much happens if you stay below 200℃, and even with high temperatures and long times, it’s hard to get above 8%. Still, deep-frying with the same oil for days on end seems like a bad idea.

And a note for Americans: If your food has less than 0.5 grams of trans fats per serving, then it can legally be labeled as having “zero” trans fat. Cooking oils typically have a serving size of a tablespoon (14g), meaning that the “zero trans fat” threshold is around 3.6% trans fat. Companies apparently respond to this by diluting their trans-fat-containing products with regular vegetable oil just enough to get down to 3.6%. Ain’t capitalism grand?

Anyway, trans fats seem like a good lesson about unintended consequences and how we should be careful about screwing around with what we eat.

Trans fats are also sometimes suggested as a reason that animal fats might be healthier than vegetable fats: Animal fats are mostly saturated fat, and saturated fat cannot become trans because it has no double bonds.

The outside view

Much of this is plausible.

There’s lots to like about seed oil theory. I’m sympathetic to the idea that the modern Western diet is somehow fundamentally broken. (Look at what’s happening to us!) Even if we don’t understand exactly why, it looks like “processing” is bad, and seed oils sure are processed.

The suggested mechanisms for seed oils to be harmful seem plausible, too. I could believe that omega-6 fats cause oxidization or inflammation or that saturated fats might make you feel more full. Experts seem to agree that most people should eat more omega-3 fats.

And if you want a monocausal story for every modern health problem, inflammation is a good mechanism. We have other cases where one source of inflammation causes a range of seemingly unrelated health problems (e.g. air pollution).

Finally, seed oil theorists often suggest replacing unsaturated fat with saturated fat. This conflicts with the old consensus that saturated fat increases the risk of heart disease. But there seems to be increasing doubt about that old consensus (Astrup et al. 2020). Many still defend it, but there’s real debate.

So that’s good. But there are also reasons for doubt.

But correlation ⇏ causation.

Just because two things happened at the same time doesn’t mean one caused the other. Maybe there’s some causal relationship, or maybe it’s just random. Let’s not belabor this.

And it’s a complex mechanistic argument.

Yes, there are plausible mechanisms for seed oils to hurt us. I agree! But complex mechanistic arguments for diet do not have a good track record. So far they’ve worked for… basically nothing? (We’re still debating if eating salt or cholesterol are bad for you.)

When humans build complex systems, we modularize, so we can understand what’s happening. But evolution is a lunatic. It doesn’t care about understanding. So biological systems tend to be spectacularly non-modularized. When I started reading Molecular Biology of the Cell I almost felt like I wanted to throw up, what with all the exceptions to the exceptions to the exceptions.

Did you know that dogs sneeze to signal they’re feeling playful? I guess this happened because evolution wanted a way to signal playfulness, so why not just use an existing instinct for expelling particles? It’s a little confusing, but no big deal, right? Our bodies are a collection of millions of these kinds of hacks stacked on top of each other.

Maybe the mechanisms people give for seed oils are right. I’m no expert, and I’ve exhausted the patience of everyone I know who is. But there are 8 billion other interacting mechanisms. Above all, I don’t understand why seed oil theorists are so damned confident. It’s fine to speculate about mechanisms, but you do that for choosing what to investigate experimentally, not as a final source of truth.

And seed oil theories have features that make them hard to falsify.

For example:

  • There are many variants of these theories. Is it all vegetable oil that’s bad, or just seed oil? Is olive oil OK? Or is it unsaturated fat, polyunsaturated fat, omega-6 fat, or just linoleic acid? Is it the omega-6:3 ratio, and if so then why avoid canola oil with its extremely low ratio? People who criticize one theory are often told they aren’t arguing against the One True seed oil theory. But what is that?
  • Say some study gives some people more seed oil, and those people are fine. Is that evidence against seed oil theory? Some say no, because the harms of seed oil are nonlinear—they mostly hurt you when you cross over some threshold. If people were already past that threshold before the study started, then adding additional seed oil wouldn’t do more harm.
  • Or say you reduce seed oils and don’t get healthier. Evidence against seed oil theory? Again, some say no, because you can’t “un-ring the bell”. When you eat seed oils, you cause your body to get dis-regulated. But fixing your diet won’t make you well-regulated again, because the damage is done.
  • People often report switching seed oils out for saturated fats and failing to lose weight. A common response is they should look at waistline size, not total weight.
  • Say some trial shows that reducing sugar has a big effect. That might suggest that seed oils aren’t everything. But some just see this as further proof of seed oil’s primacy—it’s because of seed oil that the sugar is able to do harm.

All of these things are possible. Maybe an invisible dragon really does live in your garage. But the more such features a theory has, the less I trust it.

Some seed oil theorists are selling stuff.

Some of the big seed oil theorists run companies that sell seed-oil free products. I guess this is a conflict of interest, but… if you thought seed oils were killing everyone, wouldn’t you want to help provide alternatives? I’m more worried about the internet’s usual trick of corrupting everything by showering attention on the overconfident.

The inside view

Human RCTs mostly say saturated fat is bad.

If you replace butter with seed oil, what happens? The best way to answer this question is to try it. Fortunately, many trials have been done. I stress: many. In such cases, we shouldn’t stress about individual results because anything can happen in one trial, from p-hacking to fraud to contaminated coconut oil.

The thing to do is look at trials as a whole. Ideally, using a standard methodology. Enter Hooper et al. (2020), who did a honking meta-analysis of randomized trials in which saturated fat was reduced as part of the (highly respected) Cochrane project. They found that getting more of your overall energy from saturated fat was bad:

In more detail, they found that the groups that got less saturated fat:

  • Had a 21% reduction in cardiovascular events.
  • Had small (3-6%) non-statistically significant reductions in overall mortality, cardiovascular mortality, and cancer.
  • Had cholesterol that looked slightly better by most measures.
  • Were an average of 1.8 kg (4 lb) lighter.
  • Had no apparent change in cancer mortality, diabetes, or blood pressure.

This seemed to be true regardless of if saturated fat was replaced with polyunsaturated fat or carbohydrates. (There were few trials where it was replaced with monounsaturated fats or protein.)

These meta-analyses are our most important information. Averaged over decades of studies, replacing saturated fats with polyunsaturated fats (i.e. replacing butter with seed oil) seems to be good for you, not bad for you.

I don’t see this as conclusive, or even close to conclusive. We really need more, bigger, better trials. But at the moment, the experimental evidence suggests vegetable oil is good, not bad.

There’s no conspiracy against the Sydney Diet Heart Study.

The Sydney Diet Heart Study study ran from 1966 to 1973. In it, 458 middle-aged men with a recent coronary event were randomized to either continue their normal diet or to substitute safflower (seed) oil for saturated fat. The group with the extra seed oil had lower cholesterol, but did worse both in terms of all-cause mortality, and cardiovascular disease.

Seed oil theorists talk about this trial a lot. It was a good trial! And the results aren’t good for seed oil. But it is included in the meta-analysis. Look:



In analysis after analysis, it’s sitting there, being taken into account. Along with all the other studies, which mostly don’t support the same conclusion. The Nutrivore points out that the vegetable oil group got Miracle brand margarine which was high in trans fats. That could explain their poor results, but the other group was surely eating some trans fats too, and this kind of single-trial nitpicking makes me nervous.

There’s no conspiracy against the Minnesota Coronary Survey either.

The Minnesota Coronary Survey ran from 1968 to 1973. There’s a story floating around that goes something like this: This was a huge trial with 9,423 subjects in nursing homes and mental hospitals. For the experimental group, they replaced saturated fat with vegetable oil rich in lionleic acid. They expected this to decrease heart disease, but when the opposite happened, the investigators just kind of dropped things. These “inconvenient” results were mostly ignored until 43 years later, when Ramsden et al. (2016) came around and recovered the old data.

When I read this story I was pumping my fist. Fixing publication bias by scrounging up lost data from decades ago! Yes! But when I looked into the details, that story is mostly bogus. The main results of this trial have been available for decades. Here is Figure 6 from Frantz et al. (1989), which clearly shows that the control group does a bit better:

Some say that even if the results were published, they were ignored before Ramsden et al., but that’s not true either. Check the citations if you want—most come before 2016.

Now, this study is not in the meta-analysis. They excluded it because there were high dropout rates, meaning the average subject was only in the trial for only one year. It was also very weird by modern standards—they created fake meat and cheese where the natural fats were replaced with vegetable oil. (There’s a whole sub-debate about if that vegetable oil contained trans fat. We’ll probably never know because the records are lost and no one who might remember is still alive.)

The exclusion of this study is no conspiracy. Lots of trials where vegetable oils look great were also excluded. For example, the legendary Finnish Mental Hospital trial ran for 12 years and found that a similar (also weird) diet reduced heart disease by almost 50% and overall mortality by 11%. It was excluded because it used a crossover design rather than randomization.

If you want different inclusion criteria, fine! Argue that your criteria are better, and do a new meta-analysis. But ad-hoc inclusion and exclusion of individual studies is a recipe for getting answers that fit with your preconceptions. Just look at the track record of using polling data to predict elections.

Public health authorities mostly say saturated fat is bad.

I’ve seen people claim that public health authorities in “other countries” support substituting saturated fats for unsaturated fats. This, for the record, is untrue. I looked up the official advice of all the G7 countries plus the WHO, Spain and Australia:

CountryTotal FatSaturated FatVegetable oilOther
United States LimitPrefer 
GermanyLimit Prefer 
FranceLimitLimit Eat more α-LA good
ItalyLimitLimitPreferLimit heat for unsaturated fats
Spain LimitPreferOlive oil good
Canada LimitPreferLimit palm/coconut oil
Australia LimitPrefer 
JapanLimit  “Enjoy your meals”

Seed oil folks often bring up the French paradox, the (controversial) claim that French people are/were thin and have low cardiovascular disease despite eating lots of saturated-fat-rich croissants or whatever. And I guess France comes closest to the seed oil position, since they don’t endorse vegetable oils and suggest increasing α-LA, an omega-3 fat. But France still says to limit saturated fat. Japan seems focused on other things.

Seed oils don’t seem to cause inflammation.

The most comprehensive meta-review I could find (Johnson and Fritsche, 2012) looked at trials that increased linoleic acid or omega-6 fats (basically, seed oils). It found that “virtually no data” existed to support the idea that this increased inflammation.

Beyond that, the suggested “LA → AA” mechanism seems to be basically disproven. The problem is that metabolism of linoleic acid (LA) into arachidonic acid (AA) saturates at low levels of LA consumption (Liou and Innis 2009). A meta-review (Rett and Whelan, 2011) found that many different trials that decreased LA by up to 90% or increased it by up to 600% all seemed to do basically nothing:

It’s not clear if the timelines work out.

True, seed oil consumption has skyrocketed along with obesity. But hold on. If seed oil consumption is causing obesity, then people should have started getting fat after seed oils started increasing. Did they?

Blasbalg et al. (2011) give some long-term estimates of vegetable oil consumption: (Note the scale is smaller in the lower plot.)

How early would obesity have to have started increasing to falsify the idea that it’s caused by seed/vegetable oil? 1970? 1940? Earlier?

Now, when did people start gaining weight? This is tricky, because nobody was collecting BMI statistics back in the 1700s. But Kromlos and Brabec (2010) use a set of surveys taken between 1959 and 1994 and fit a regression to predict weight at age 50 from birth year. They then use this to extrapolate back to people born as early as 1882. (I think because someone born in 1882 would have been 77—and still hopefully alive—in 1959?) This gives this graph we saw earlier, with a long-term trend of people at the median gaining around 0.05 BMI/year:

While it looks like people were getting heavier back in the 1880s, I emphasize that the evidence is very weak: The leftmost part of the plot is an estimate for men born in 1882 in 1932 (when they were 50) based on data collected in 1959.

There’s also data for the incoming classes at a couple military academies. Hiermeyer (2010) collects data for people entering West Point and the Citadel:

Maybe West Point cadets got a little heavier? There’s a 20 year run, so at 0.05 BMI/year we’d only expect an increase of 1 BMI, close to what’s observed. But for the Citadel, if anything is decreasing. Coclanis and Komlos (1997) give more Citadel data, stratified by the age of the students:

Birth Decade151617181920

Again, it looks like not much changed between those born in the 1870s and the 1900s. But things started to pick up for those born in the 1920s.

All this data suggest people starting getting heavier during the 1920s or even earlier, when seed oil consumption was still very low. So I see this as some evidence against seed oil theory.

Of course, none of this data is very good. Surely there’s more long-term data on weight lurking out there somewhere? Typically, seed oil theorists point at data only going back to 1970 or so, but that will never prove anything, since obesity was already increasing at that time. We need to go back further.

Omega-6 doesn’t explain inter-country obesity.

People in different countries eat different amounts of seed oil. If eating seed oil makes you fat, then must per-country seed oil consumption correlate with per-country obesity?

Not necessarily, no. But I decided to check anyway. I found the WHO provides some amazing data for obesity—the estimated fraction of the population that has a BMI of at least 30 by year. Here’s what that looked like in 2010.

(There’s no data for South Sudan because it didn’t exist in 2010. There’s no data for Antarctica because all the people there are penguins. I think there’s no data for Greenland/French Guiana because they’re considered part of Denmark/France. There’s no data for Taiwan because the WHO is afraid of China. I don’t know the deal with Turkey and Kosovo.)

The USA isn’t quite #1—It’s beaten by Egypt, the Bahamas, Kuwait, and a bunch of tiny island nations. American Samoa is way ahead at 71.63%.

Anyway, seed oil consumption data is harder to find, but Micha et al. (2014) give estimates for 2010. Here’s estimated omega-6 consumption:

Can you see a relationship with obesity? I couldn’t, so I made a scatterplot with one circle per country. (Click to zoom in and see country codes.)

Is anything there? Maybe so, I’m not sure. I did the same for saturated fat and all fat, which look about equally convincing. But if you put per-capita GDP on the x-axis…

Could it be that something else is going on here?

On distraction

A weak version of seed oil theory is that seed oils are highly processed, so why not use cold-pressed olive oil instead? If that’s the theory, fine. In fact, this is mostly what I do myself. I figure it might be useless, but it’s unlikely to be harmful, and olive oil is delicious.

And I wouldn’t be shocked if one of the suggested mechanisms for seed oil turns out to be valid. I wouldn’t be surprised at all if some mechanism turned out to be part of a larger, more complicated story.

And in practice, avoiding seed oils is probably really good for you, because it forces you to eliminate most of the processed crap you shouldn’t be eating anyway.

A middle-strength theory would be that seed oils might be harmful, so it’s safest to reduce seed oils and replace them with saturated fat. I disagree with this, because the balance of evidence says that saturated fat is more risky than unsaturated fat (monounsaturated or polyunsaturated). But I guess it’s not totally crazy.

But seed oil theorists mostly seem to push a much stronger theory: We know that seed oils are the cause of Western disease.

I’ll just be honest. I think this view is completely indefensible. I feel embarrassed when I see people promoting it. You’re sure? How? I don’t see any way to get to this conclusion other than heavily filtering the evidence—ignoring the flaws in everything that supports a predetermined view while scrambling to find flaws in everything that contradicts it.

Again, I’m sure you can send me long lists of random citations. (You don’t need to send them; it’s OK; I’ve seen them already.) But for anything that’s been studied in detail, there’s always lots of evidence to support any semi-plausible view. Do you have any idea how much evidence people can produce for UFOs or chronic Lyme or colloidal silver?

My real worry about seed oil theory is that it’s a distraction. If you want to be healthier, we know ways you can change your diet that will help: Increase your overall diet “quality”. Eat lots of fruits and vegetables. Avoid processed food. Especially avoid processed meats. Eat food with low caloric density. Avoid added sugar. Avoid alcohol. Avoid processed food.

I know this is hard. You could even argue it’s unrealistic. That wouldn’t make it wrong.

Look, I wish strong seed oil theory were true. That would be great. All we’d have to do is reformulate our Cheetos with different oil, and then we could go on merrily eating Cheetos. Western diet without Western disease! Sadly, I think this is very unlikely.

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The biggest question on my mind right now is, what does your friend think of this post now that you've written it? 

If I hadn't heard back from them, would you want me to tell you? Or would that be too sad?

2Kabir Kumar
I want to know.
Need to know.

I owe my current health good to one especially shady anti-seed oil theorist on twitter.

Tl;dr: For me, one key problem with seed oils is their likelihood of being contaminated with glyphosate, commonly known as the weedkiller Round-Up and increasingly used as a pre-harvest dessicant (also widely recognized as a microbiome disruptor).

As an n=1 case study, I don't claim that glyphosate is the cause of Western disease, only that glyphosate and other microbiome-disruptors seem more likely to be a primary causes of western disease than any other reason discussed in this article and that I have compelling evidence that glyphosate was almost surely the direct cause of my problems.

What follows is my own experience attempting to troubleshoot my health problems. 
- After moving to the UK, I adapted my diet based on local availability. I mostly cook my own food, sticking better than most people around me to the principles of healthy eating listed towards the end of this article. I had no history of gut issues, no problems eating out.
- I started getting an acid reflux feeling after meals.
- Over about 6 months, this increased in severity and neither readily google-able tips nor advice from m... (read more)

This bit caught my eye:

This strong response made me fairly sure that most cheap olive oils in both the US and the UK are (probably illegally) cut with rapeseed oil.

I searched for [is olive oil cut with canola oil] and found that in the twenty teens organized crime was flooding the market with fake olive oil, but in 2022 an EU report suggested that uplabeling to "extra virgin" was the main problem they caught (still?).

Coming from the other direction, in terms of a "solid safe cheap supply"... I can find reports of Extra Virgin Olive Oil being sold by Costco under their Kirkland brand that is particularly well sourced and tested, and my priors say that this stuff is likely to be weirdly high quality for a weirdly low price (because, in general, "kirklandization" is a thing that food producers with a solid product and huge margins worry about). I'm kinda curious if you have access to Kirkland EVOO and if it gives you "preflux"?

Really any extra data here (where your sensitive palate gives insight into the current structure of the food economy) would be fascinating :-)

5David Cato
Next time I have a chance to pick up Kirkland olive oil I'll give it a try and report back.  I made a decision around this time of dietary changes to stop trying to cut so many corners wtih food. As a calorie dense food, even paying an "outrageous" double or triple the cost of cheap olive oil barely dents the budget on a cost per calorie basis. And speaking of budgeting, I had mental resistance to spending more on food so now I guesstimate what percent of my food budget I spend over the "cheapest equivalent alternative" part and I label as "preventative healthcare".
I look forward to your reply! (And regarding "food cost psychology" this is an area where I think Neo Stoic objectivity is helpful. Rich people can pick up a lot of hedons just from noticing how good their food is, and formerly poor people have a valuable opportunity to re-calibrate. There are large differences in diet between socio-economic classes still, and until all such differences are expressions of voluntary preference, and "dietary price sensitivity has basically evaporated", I won't consider the world to be post-scarcity. Each time I eat steak, I can't help but remember being asked in Summer Camp as a little kid, after someone ask "if my family was rich" and I didn't know, about this... like the very first "objective calibrating response" accessible to us as children was the rate of my family's steak consumption. Having grown up in some amount of poverty, I often see "newly rich people" eating as if their health is not the price of slightly more expensive food, or their health is "not worth avoiding the terrible terrible sin of throwing food in the garbage (which my aunt who lived through the Great Depression in Germany yelled at me, once, with great feeling, for doing, when I was child and had eaten less than ALL the birthday cake that had been put on my plate)". Cultural norms around food are fascinating and, in my opinion, are often rewarding to think about.)
This is shockingly similar to what I'm going through.  And the fries that fucked me up the other night are indeed fried in canola oil. I'm cautiously optimistic but I know how complicated these things can be -_-. Will report back!
1David Cato
I wish you the best and look forward to hearing how it goes.
2[comment deleted]

Correlation to increased consumption of hidden trans fats looks like a promising angle for figuring out some of the conflicting data.

I don't have a cite handy, but proportion of free acids was found to strongly increase with repeated heating of vegetable oils in cooking. There's a story here where pufa is more fragile, and incorporation of damaged fats into bodily tissue is not good. In particular, fat cells made up of damaged fats might mess with normal lipid balance processes. This is one possible story for why processed meats are so bad. We'd be doubling up on this process, feeding animals such that they have lots of damaged fats in their tissues (eg we feed pigs expired candy because it is cheap, and high BMI is desirable), killing and processing them such that it's even more damaged, and then eating it.

Overall, I'm bullish on the story that processing is bad, potentially through multiple mechanisms.

I'm bearish on pufa being bad in generality, if it were I don't think we'd see some of the strongest effects in nutrition science on reduced mortality from nuts and fish. I personally consume both raw on the processing is bad story.

8Alex K. Chen (parrot)
It depends on how processed the PUFA is - many PUFAs in processed foods are highly heated up. Processing PUFAs in high heat is what causes peroxidizeable aldehydes/acrolein/9-HNE/advanced lipid peroxidation end-products (ALEs)/etc But PUFAs in soybeans (or sunflower seeds w/o extra procesing) themselves are way less likely to be bad, and this is what the epidemiological evidence hints at. For whatever reason, PUFAs are VERY strongly protective against heart disease (b/c they lower LDL) and insulin resistance. These are the leading causes of death on western populations, but this does not make PUFAs equally protective on all diseases, especially those who already have very low risk of death from heart disease/insulin resistance. Fish oil (omega-3's) are also WAY more easily damaged/peroxided than even omega-6's. People usually don't fry food with omega-3's the way they do with omega-6's, but if they did, would we see the opposite association with omega-3's that we usually see? [note omega-3's still fail to increase lifespan as per ITP] What I am concerned is if they change cell membrane composition long-term in a way that makes cell membranes more easily peroxidized (animals with more saturated lipid membranes live longer, though there are ways to fix the damage, as Gustavo Barja knows - Longevity and Evolution (Aging Issues, Health and Financial Alternatives) 1 ) Whether omega-6's convert into pro-inflammatory or anti-inflammatory metabolites of arachidonic acid (BOTH are possible) depends highly on one's D6D genotype. more info I collected:

Seed oil folks often bring up the French paradox, the (controversial) claim that French people are/were thin and have low cardiovascular disease despite eating lots of saturated-fat-rich croissants or whatever.

As a French person hearing about this for the first time, that claim indeed seems pretty odd.

If I was asked to list the lifestyle differences between France and the US with the most impact on public health, I would think of lower car dependency, higher access to farmer's markets, stricter regulations on industrial food processing (especially sugar content in sodas), smaller portions served in restaurants, pharmacies not doubling as junk food shops, the absence of food deserts, public health messaging (eg every junk food ad having a "please don't eat this, kids" type disclaimer) etc... way before I thought of the two croissants a week I eat.

Viennoiseries are an occasional food for most people, not a staple. Now if you wanted to examine a french-specific high-carb staple, baguettes are a pretty good options: almost all middle-class households buy one a day at least.

3Lev Protter
There is also a similar, lesser known "Israeli Paradox", where we consume less saturated fat and more unsaturated, and have worse cardiovascular stats.
French are also apparently slightly less obese than their neighbours, the difference is not only with the US.
They seem to have similar average BMI and the Swiss seem to have an even lower obesity rate.  Belgium seems lower obesity rates than France but slightly higher average BMI. Andorra has lower obesity rates but a significantly higher average BMI. The UK, Spain and Germany are doing worse than France.  A bit of chatting with Gemini suggests what Belgium, France and the Swiss share is a strong market culture so food is more fresh.
Or maybe speaking french automatically makes you healthier. I'm gonna choose to believe it's that one.
And they all eat a lot of butter and dairy products.
That really depends of which part of France you are talking about. Provence uses mostly olive oil. In the South West they often use duck fat.


I do sure wish this question had easier answers, but I appreciate this post laying out a lot of the evidence.

I do have some qualms about the post, in that while it's pretty thorough on the evidence re: seed oils, it sort of handwavily assumes some other nutrition stuff about processed foods that (I'm willing to bet) also have highly mixed/confusing evidence bases. But, still thought the good parts of the post were good enough to be worth curating.

Yeah, I'd be willing to bet that too.

Great post, enjoyed it!

A technical mistake here: "Fat is made of fatty acids—chains of carbon atoms linked via hydrogen bonds". They are linked via covalent bonds, not hydrogen bonds.

For those who don't know: covalent bond is a strong chemical bond that forms when two atoms provide one electron each to form an electron pair. These are, like, normal bonds that hold molecules together. They are shown as sticks when one draws a molecule. Hydrogen bond is much weaker intermolecular bond that forms when one molecule has an atom with unshared electron pair and the other has a hydrogen atom that sort-of has an orbital to fit this electron pair.

And also having a chain of carbon atoms is about "fatty" part, and the "acid" part means that at the end of this chain sits carboxyl group. I know that's not the point of this post, it just hurts a little, I'm sorry.

Thanks for this piece. I admit I have always had a bit of residual aversion to seed oils that I've struggled to shake.

Having said that, as you're pushing so strongly against seed oils in favour of "processing" as a mechanism for poor health, I think I need to push back a bit.

If you want to be healthier, we know ways you can change your diet that will help: Increase your overall diet “quality”. Eat lots of fruits and vegetables. Avoid processed food. Especially avoid processed meats. 

"Avoid processed food" works very well as a heuristic - far better than anything like the "nutrition pyramid", avoiding saturated fats/sugars or calorie counting etc. But it also seems like something that should annoy people who like clear thinking and taxonomies. 

As you note, "processing" includes hundreds of processes, most of which have no plausible mechanism by which they might harm human health. Articles describing the ultra-processed taxonomy often just list a litany of bad-sounding things without an explanation why they're bad e.g. "mechanically separated meat", "chemical modifications" and "industrial techniques". Most of these are either benign when you think about it (we'd all prefer... (read more)

It seems pretty straightforward to me but maybe I'm missing something in what you're saying or thinking about it differently. Our bodies evolved to digest and utilize foods consisting of certain combinations/ratios of component parts. Processed food typically refers to food that has been changed to have certain parts taken out of it, and/or isolated parts of other foods added to it (or more complex versions of that). Digesting sugar has very different impacts depending on what it's digested alongside with. Generally the more processed something is, the more it differs from the way that our bodies are optimized for. To me "generally avoid processed foods" would be kinda like saying "generally avoid breathing in gasses/particulates that are different from typical earth atmosphere near sea level". It makes sense to generally avoid inputs to our machinery to the extent that those inputs differ from those which our machinery is optimized to receive, unless we have specific good reasons. Why should that not be the default, why should the default be requiring specific good reasons to filter out inputs to our machinery that our machinery wasn't optimized for?
I think your intuitions are generally correct, and as I say, it's usually a good heuristic to avoid overly processed food. In the absence of other evidence, if you're in a food market where everything is edible, you should probably opt for the less processed option. I also don't disagree with it playing a role in national health guidelines. But it's a very imprecise heuristic, and I think LessWrong-ers with aspirations to understand the world more accurately should feel a bit uncomfortable with it, especially when benign and beneficial processes are lumped together with those with much clearer mechanisms for harm. 
People have been breathing a lot of smoke in the last million years or so, so one might think that we would have evolved to tolerate it, but it's still really bad for us. Though there are certainly lots of ways to go wrong deviating from what we are adapted to, our current unnatural environment is far better for our life expectancy than the natural one. As pointed out in other comments, some food processing can be better for us.
There's some simple processes that make it easier/possible to digest whole foods that would otherwise be difficult/impossible to healthily digest, but I don't really think there's meaningful confusion as to whether that's being referred to by the term processed foods. Could you offer some examples of healthy foods /better for us foods that are processed such that there would be meaningful confusion surrounding the idea of it being healthy to avoid processed foods, according to how that term is typically used? I can think of some, but definitely not anything of enough consequence to help me to understand why people here seem so critical of the concept of reducing processed foods as a health guideline.
Sure. One such example would be traditional bread. It is made from grain that is ground, mechanically separated, biotechnologically treated with a highly modified yeast, mechanically treated again and thermally treated. So it is one of the most processed foods we have, but is typically not included as "ultra-processed". Or take traditional soy sauce or cheese or beer or cured meats (that are probably actually quite bad) or tofu... So as a natural category "ultra processed" is mostly hogwash. Either you stick with raw foods from the environment we adapted to, which will allow you to feed a couple million people at best or you need to explain WHICH processing is bad and preferably why. All non traditional processing is of course a heuristic you can use, but it certainly not satisfactory as a theory/explanation. Also some traditional processes are probably pretty unhealthy. Like cured meats, alcoholic fermentation, high heat singeing and smoking depending on the exact process come to mind
I would consider most bread sold in stores to be processed or ultra processed and I think that's a pretty standard view but it's true there might be some confusion. I would consider all of those to be processed and unhealthy and I think thats a pretty standard view, but fair enough if there's some confusion around those things. I guess my view is that it's mostly not hogwash? The least healthy things are clearly and broadly much more processed than the healthiest things.
I don't have a strong opinion because I think there's huge uncertainty in what is healthy. But for instance, my intuition is that a plant-based meat that had very similar nutritional characteristics as animal meat would be about as healthy (or unhealthy) as the meat itself. The plant-based meat would be ultra-processed. But one could think of the animal meat as being ultra-processed plants, so I guess one could think that that is the reason that animal meat is unhealthy?
Mostly because humans evolved to eat processed food. Cooking is an ancient art, from notably before our current species; food is often heavily processed to make it edible (don't skip over what it takes to eat the fruit of the olive); and local populations do adapt to available food supply.
There's a taxonomy now for levels of processing (NOVA groups); most research only finds problems with the highest level of processing (NOVA 4), which includes processing methods you can't do in an ordinary kitchen, or that were not possible ~100 years ago (extrusion, moulding, preprocessing by frying are some examples given).
Do you happen to have any recommended pointers for research on health impacts of processed food? It's pretty easy to turn up a few recent meta reviews, which seems like a decent place to start, but I'd be interested if there were any other sources, particularly influential individual experiments, etc. (It seems like there's a whole lot of observational studies, but many fewer RCTs, for reasons that I guess are pretty understandable.) It seems like some important work here might never use the word "processing".
I don't remember individual studies but two books that might be helpful: Ultra-Processed People by Chris van Tulleken Metabolical by Robert Lustig  UPP is terribly written and I imagine mostly useful for its bibliography (I skimmed it in an hour or so). Metabolical is better (although far too difficult a read to be a successful popsci book), although it isn't specifically focused on processing techniques (it in particular discusses stripping out fibre, adding sugars, reducing water, as some major processing techniques with big issues). You might find something helpful looking in the refs section of either book. 
Also as a brief pointer at another cool thing in Metabolical, Lustig claims that exercise is useful for weight loss mostly because of its beneficial impact on cell repair/metabolic system repair (something specific about mitochondria?) and not for the calorie deficit it may or may not create. I consider Lustig's science to be quite thorough, I like him a lot. The main point against him is that he personally doesn't look very metabolically healthy, which I would expect of someone who had spent his life investigating and theorising about what influences metabolic health. 
Thanks for the reference! I'm definitely confused about the inclusion of "pre-prepared (packaged) meat, fish and vegetables" on the last list, though. Does cooking meat or vegetables before freezing it (rather than after? I presume most people aren't eating meat raw) actually change its processed status significantly?
I suspect the word 'pre-prepared' is doing a lot of the heavy lifting here--when I see that item on the list I think things like pre-fried chicken, frozen burger patties, veggie pakora, veggies in a sauce for a stir-fry, stuff like that (like you'd find in a ready-made frozen meal). Not like, frozen peas.
Yeah, it'd be helpful to know what heavy lifting is going on there, because I feel like there's a pretty strong distinction between 'frozen burger patties that are otherwise indistinguishable from unfrozen burger patties' and 'TV dinner'.
A cooked food could technically be called a processed food but I don't think that adds much meaningful confusion. I would say the same about soaking something in water. Olives can be made edible by soaking them in water. If they're made edible by soaking in a salty brine (an isolated component that can be found in whole foods in more suitable quantities) then they're generally less healthy. Local populations might adapt by finding things that can be heavily processed into edible foods which can allow them to survive, but these foods aren't necessarily ones which would be considered healthy in a wider context.
Aside from the rare naturally edible-when-ripe cultivar, olives are (mostly) made edible by fermenting and curing them. With salt, yes. And lye, often. Even olives fermented in water are then cured in brine. What saltless olives are you interacting with? Edit: Also, cooking is very much processing food. It has all the mechanisms to change things and generate relevant pollutants. It changes substances drastically, and different substances differently drastically. Cooking with fire will create smoke, etc. Cooking with overheated teflon cookware will kill your birds. Mechanisms are important. And, yes, soaking food in water, particularly for the specific purpose of cultivating micro-organisms to destroy the bad stuff in the food and generate good stuff instead, is some intense, microscopic-level processing.
I had just searched on google about ways to make olives edible and got some mixed results. The point I was trying to make was that the way that olives are typically processed to make them edible results in a product that isn't particularly healthy at least relatively speaking, due to having isolated chemical(s) added to it in its processing. The main thing I'm trying to say is that eating an isolated component of something we're best adapted to eat, and/or adding isolated/refined components to that food, will generally make that food less healthy than it would be were we eating all of the components of the food rather than isolated parts. I think that process, and more complex variations of that process, are essentially what's being referred to when referring to the process behind processed foods. I think it's a generally reasonable term with a solid basis.
Hmm, while I don't think olives in general are unhealthy in the slightest (you can overload on salt if you focus on them too much because they are brined, but that's reasonable to expect), there is definitely a meaningful distinction between the two types of processing we're referencing. Nixtamalization isn't isolating a part of something, it's rendering nutrients already in the corn more available. Fermenting olives isn't isolating anything, (though extracting olive oil is), it's removing substances that make the olive inedible. Same for removing tannins from acorns. Cooking is in main part rendering substances more digestible. We often combine foods to make nutrients more accessible, like adding oil to greens with fat-soluble vitamins. I do think there's a useful intuition that leaving out part of an edible food is less advantageous than just eating the whole thing, because we definitely do want to get sufficient nutrients, and if we're being sated without enough of the ones we can't generate we'll have problems. This intuition doesn't happen to capture my specific known difficulty with an industrially processed additive, though, which is a mild allergy to a contaminant on a particular preservative that's commonly industrially produced via a specific strain of mold. (Being citric acid, there's no plausible mechanism by which I could be allergic to the substance itself, especially considering I have no issues whatsoever with citrus fruits.) In this case there's rarely a 'whole food' to replace - it's just a preservative.
I would consider adding salt to something to be making that thing less healthy. If adding salt is essential to making something edible, I think it would be healthier to opt for something that doesn't require added salt. That's speaking generally though, someone might not be getting enough sodium, but typically there is adequate sodium in a diet of whole foods. I would disagree that adding refined oil to greens would be healthy overall. Not sure how much oil we're talking, but a tablespoon of oil has more calories than an entire pound of greens. Even if the oil increases the availability of vitamins, I am very sceptical that it would be healthier than greens or other whole plants with an equivalent caloric content to the added oil. I believe it's also the case that fats from whole foods can offer similar bioavailability effects. At the same time, as far as I'm aware some kinds of vinegar might sometimes be a healthy addition to a meal, despite it's processing being undoubtedly contrary to the general guidelines I'm defending, so even if I don't agree about the oil I think the point still stands. I do think you're offering some valid points that confound my idea of simple guidelines somewhat, but I still don't think they're very significant exceptions to my main point. Appreciate the dialogue:)
  I'd say it's too strong a claim that adding salt makes things less healthy. Remember that humans, eating generally mostly plants but some meat as well, developed rather strong craving for sodium salt, just like most herbivorous mammals. If you eat enough meat (not boiled) you don't need more sodium, if you eat a little meat or a lot but boiled, it's probably better to add some. If you eat only potatoes, you'll die without added salt (just kidding, who eats only potatoes).
If you only eat potatoes you wouldn't die from lack of sodium, the average person would probably become healthier only eating potatoes, it's been done, though I'm not endorsing that. Potatoes and water already have sodium in them, maybe not quite at the ideal ratio per average calorie but it's pretty close or maybe in that range depending on the person. We certainly need some sodium/salt but I think the extent to which most people crave salt is a result of miscalibration due to overexposure and adaptations which aren't aligned with our current environment. I minimize added sodium and I don't really have any cravings for salt anymore, unless you count the cravings I have generally for the food/nutrition I need to sustain myself, which contains roughly enough sodium naturally. If someone is eating a varied diet of whole foods with no added salt it's possible that adding a very marginal amount of extra salt would be healthier in some cases, but that's very far from what is typical.
But then why do medicine portals advise us to be wary of risks associated with too low sodium? It's claimed to cause insulin resistance, a higher risk of heart disease, hyponatremia, and whatnot. People with any-cause hyponatremia can cure their symptoms with more salt. These people here[1] claim that it's probably not good for healthy people to artificially (i.e. against their natural desire) restrict their sodium. After reading these claims, what's the main good side of reducing sodium intake to pretty low?  1. ^
Generally the hypothesis is that most people will get more sodium in their diet than they crave with their natural desire, if they just eat the food of least resistance (cheapest or easiest, most shelf stable, whatnot). A lot of the sodium that gets into your diet is not so richly activating your taste buds as table salt applied to taste. What we want overall with salinity is to preserve it at a level that's correct for us, because we take it in through our diet and excrete it through various processes like sweat. Excessive salt consumption doesn't directly affect your overall salt and water balance that much, because the body has hormonal regulation of various mechanisms to keep it stable - it's presumably the overworking of these mechanisms that causes health issues, which is much preferable than it causing issues directly if you've seen the effects of the wrong salinity on cells in a petri dish under a microscope. (The effects on whatever cells I was looking at, which started at a neutral salinity: Raising the salinity (saltier) caused them to shrivel up and dessicate like raisins; lowering the salinity (less salty) caused them to explode.)
It's my understanding that the controversy is mostly manufactured by industries with large financial interests in selling foods with added sodium. They pay for misleading/inaccurate studies to be done in order to introduce uncertainty and doubt. Whereas it's my understanding there is a near consensus towards low sodium amongst scientists without direct/indirect industry ties. I do think there are probably some cases where increasing salt beyond natural levels can be the healthier thing to do given specific health concerns.
We're talking about a tablespoon of (olive, traditionally) oil and vinegar mixed for a serving of simple sharp vinaigrette salad dressing, yeah. From a flavor perspective, generally it's hard for the vinegar to stick to the leaves without the oil. If you aren't comfortable with adding a refined oil, adding unrefined fats like nuts and seeds, eggs or meat, should have some similar benefits in making the vitamins more nutritionally available, and also have the benefit of the nutrients of the nuts, seeds, eggs or meat, yes. Often these are added to salad anyway. You probably don't want to add additional greens with the caloric content of oil to a salad; the difference in caloric density means that 1 tablespoon of oil translates to 2 pounds of lettuce (more than 2 heads), and you're already eating probably as many greens as you can stomach! Edit: I should also acknowledge that less processed (cold pressed, extra virgin, and so forth) olive oil has had fewer nutrients destroyed; and may be the best choice for salad dressing. But we do need to be careful about thinking processing only destroys nutrients - cooking, again for example, often destroys some nutrients and opens others up to accessibility.
I typically consume my greens with ground flax seeds in a smoothie. I feel very confident that adding refined oil to vegetables shouldn't be considered healthy, in the sense that the opportunity cost of 1 Tablespoon of olive oil is 120 calories, which is over a pound of spinach for example. Certainly it's difficult to eat that much spinach and it's probably unwise, but I just say that to illustrate that you can get a lot more nutrition from 120 calories than the oil will be adding, even if it makes the greens more bioavailable. That said "healthy" is a complicated concept. If adding some oil to greens helps something eat greens they otherwise wouldn't eat for example, that's great.
Raw spinach in particular also has high levels of oxalic acid, which can interfere with the absorption of other nutrients, and cause kidney stones when binding with calcium. Processing it by cooking can reduce its concentration and impact significantly without reducing other nutrients in the spinach as much. Grinding and blending foods is itself processing. I don't know what impact it has on nutrition, but mechanically speaking, you can imagine digestion proceeding differently depending on how much of it has already been done. You do need a certain amount of macronutrients each day, and some from fat. You also don't necessarily want to overindulge on every micronutrient. If we're putting a number of olives in our salad equivalent to the amount of olive oil we'd otherwise use, we'll say 100 4g olives, that we've lowered the sodium from by some means to keep that reasonable ... that's 72% of recommended daily value of our iron and 32% of our calcium. We just mentioned that spinach + calcium can be a problem; and the pound of spinach itself contains 67% of iron and 45% of our calcium.  ... That's also 460 calories worth of olives. I'm not sure if we've balanced our salad optimally here. Admittedly, if I'm throwing this many olives in with this much spinach in the first place, I'm probably going to cook the spinach, throw in some pesto and grains or grain products, and then I've just added more olive oil back in again ... ;) And yeah, greens with oil might taste better or be easier to eat than greens just with fatty additions like nuts, seeds, meat, or eggs. 
An example where a lack of processing has caused visible nutritional issues is nixtamalization; adopting maize as a staple without also processing it causes clear nutritional deficiencies.
If this is the main reason why we should avoid ultra-processed food, then of course we'll have to avoid seed oils at any cost, as those are both ultra-processed and rather new, certainly not what we were evolved to breathe in at sea level.
I agree that seed oils should be avoided yes. I am skeptical of explanations pointing to some element particular to seed oils that is the main source of obesity and health problems, and I'd be worried this might lead people to be less concerned about consuming other unhealthy things.
One way it could be 'the processing, not the ingredients' is that in many cases the fibre is either removed or deconstructed (making it less useful in slowing down the metabolism of sugars), another is that water is removed (although I'm not sure why that's bad exactly). This is one of the key arguments endocrinologist Robert Lustig makes against industrially-processed foods, particularly ones with added sugar, bc the fibre cannot help slow down the metabolism of the sugar because it's broken up or removed.

Other commenters have already hinted at this, but I suspect that terms like "saturated fat", "seed oils", and "omega-6 PUFA" are not specific enough, and I further suspect that this makes basically all studies mostly useless (because they work with these flawed coarse terms). "Saturated fat" can be tallow from factory-farmed cows or cultured butter from grass-fed grass-finished cows (and even that isn't specific enough; was the grass sprayed with XYZ pesticide? etc.). "Omega-6 PUFA" can be highly heated seed oils chemically treated to deodorize them (masking their rancidity), or some of the oils in e.g. whole nuts. Even something specific-sounding like "extra virgin olive oil" can unfortunately mean pretty much anything because there's a bunch of fraud going on, so the actual bottle in front of you probably isn't the real thing.

My bottom line is pretty similar to yours though. Clearly something went wrong in the last few hundred years, and probably diet is a good chunk of it. So treat any kind of modern processing or ingredient with suspicion and as much as possible try to eat as humans ate before the last few hundred years.

The first graph is supposed to show " BMI at age 50 for white, high-school educated American men born in various years", but goes up 1986. But People born in 1986 are only 38 right now, so we cannot know their BMI at 50 years old. Something is wrong.

It's a regression. Just like they extrapolate backwards to (1882+50=1932) using data from 1959, they extrapolate forwards at the end. (This is discussed in the "timelines" section.) This is definitely a valid reason to treat it with suspicion, but nothing's "wrong" exactly.

My interest in the this topic arose after a rather dramatic weight increase, insulin resistance increase, liver issues, kidney issues, all showed up when I was drafted into the IDF. The main change in my diet was seed oil, because I happened to consume very little of it or any other processed foods. Another change was an increase in sugar, but the health deterioration was rapid, and happened over about 2 months before getting discharged for the above health issues, which happened to reverse back at home.

My current vague working theory is that a combination... (read more)

It seems like the US military would be the ideal institution to study this. They could effectively control the diets of soldiers, where diet control is usually a problem for most studies. Historically, the US military is also quite willing to fund research theses that mainstream academia despises like NLP's Fast Phobia cure helping soldiers with PTSD. 
I'm not sure I understand why the experience you're describing gives an update towards these seed oil theories when it seems generally consistent with already understood health and nutrition knowledge. Is it particularly surprising that someone experiences some health problems after switching from a diet low in refined/processed ingredients to one high in those ingredients, while also undergoing the stress of being drafted into the military? (I would be very stressed though I shouldn't assume) Standard nutrition might be insufficient to explain the extent and speed at which the health issues occurred, but then likewise the seed oil theories would be insufficient to explain why more drafted soldiers aren't quickly developing those same health issues.

i'm sorry not to be engaging with the content of the post here; hopefully others have that covered. but i just wanna say, man this is so well written! at the sentence and paragraph level especially, i find it inspiring. it makes me wanna write more like i'm drunk and dgaf, though i doubt that exact thing would actually suffice to allow me to hit a similar stylistic target.

(the rest of this comment is gonna be largely for me and my own development, but maybe you'll like reading it anyway.)

i think you do a bunch of stuff that current me is too chicken to try... (read more)

I would dissuade no one from writing drunk, and I'm confident that you too can say that people are penguins! But I'm sorry to report that personally I don't do it by drinking but rather writing a much longer version with all those kinds of clarifications included and then obsessively editing it down.
You might appreciate the perspective in the short post Statistical models & the irrelevance of rare exceptions. (I previously commented something similar on a post by Duncan.)

People say that meta-analyses can weed out whatever statistical vagaries there may be from individual studies; but looking of that graph of the meta-study of saturated fat, I'm just not convinced of that at all.  Like, relative risk of CVD events suddenly goes from 0.2 to 0.8 at a threshold of 9%, and then just stays there?  Relative risk of stroke goes from 0.6 at 9% to 0.9 at 12% and then down to 0.5 at 13%? Does that say to you, "more saturated fat is bad", or "there's a statistical anomaly causing this jump"?


"Clearly we are doing something wrong."

I'm going to do a quick challenge to this assumption, also: What if we, in fact, are not?

What if the healthy weight for an American individual has actually increased since the 1920s, and the distribution followed it? Alternately, what if the original measured distribution of weights is not what was healthy for Americans? What if the additional proportion of specifically 'extreme' obesity is related to better survival of disability that makes avoiding weight gain infeasible, or medications that otherwise greatly improve quality of life? Are there mechanisms by which this could be a plausible outcome of statistics that are good, and not bad?

We would still have to explain the downsides of obesity, and not just in the long-term health effects like heart disease or diabetes risks, but in the everyday life of having to carry around so much extra weight. Despite that, I'd still agree that being overweight is better than being underweight.
You don't actually have to do any adjustments to the downsides, for beneficial statistical stories to be true. One point I was getting at, specifically, is that it is better than being dead or suffering in specific alternative ways, also. There can be real and clear downsides to carrying around significant amounts of weight, especially depending what that weight is, and still have that be present in the data in the first place because of good reasons. I'll invoke the 'plane that comes back riddled in bullet holes, so you're trying to armor where the bullet holes are' meme. The plane that came back still came back; it armored the worst places, and now its other struggles are visible. It's not a negative trend, that we have more planes with damage now, than we did when they didn't come back. I do think it's relevant that the U.S. once struggled with nutritional deficiencies with corn, answered with enriched and fortified products that helped address those, and likely still retains some of the root issues (that our food indeed isn't as nutritious as it should be, outside those enrichments). That the Great Depression happened at all; and the Dust Bowl. There's questions here not just of personal health, but of history; and when I look at some of the counterfactuals, given available resources, I see general trade-offs that can't be ignored when looking at - specifically - the statistics.
Sure, I broadly agree, and I do prefer that people are living longer, even obese, than they would be with severe and long-term malnutrition. I think what you're saying here is "the modern Western diet provides a benefit in that it turns what would have been fatalities by malnutrition into survival with obesity", but please correct me if I'm wrong. Basically, it is good - very good, one of the greatest human accomplishments - that we have been able to roll back so much suffering from starvation and malnutrition. I think, though, that we can address obesity while also avoiding a return to the days of malnutrition. Or, in other words, there are three tiers, each better than the last: * Planes get shot down and pilots die * Planes get riddled with bullets but return safely * Planes don't get damaged and pilots can complete mission
Yes, but also that there might not actually be a specific new thing, a detrimental thing, to gesture at. If root causes of obesity existed all along, and changes in the modern Western diet revealed the potential for obesity in our region rather than actively causing it, looking for root causes specifically in things that have changed may not work out if the things that have changed are not the root causes. (I.e., it's a seemingly useful constraint on looking at the solution space, that might not be true -- and not so useful a constraint if it isn't.)
Ah, I think I see where you're pointing at. You're afraid we might be falling prey to the streetlamp effect, thinking that some quality specifically about Western diets is causing obesity, and restricting our thoughts if we accept that as true. I agree, and it's pretty terrifying how little we know and how much conflicting data there is out there about the causes of obesity. It might very well be that the true cause is outside of the Western diet and has little to do with it, and I could definitely see that being true given how much we've spent and how little we've gotten for research taking the Western diet connection for granted.

Thank you for taking the time to explore this domain.

There is at least one additional aspect of lipid structure consumption that is not part of your list of mechanisms. Lipid shape affects the shape of membranes. This paper illustrates the concept (tldr: Figures 3 & 4): "Understanding the diversity
of membrane lipid composition"

Figure 3 in the following review paper shows a table of different physical properties for the endoplasmic reticulum (ER), Golgi apparatus, and plasma membrane (P... (read more)


One of the things that makes mainstream nutrition hard for me to buy is the evolutionary argument.

How can saturated fats, the main ingredients in breast milk and animal products, be bad for humans (an apex predator)? Was eating animals really giving our hunter gatherer ancestors heart attacks left and right?

Similarly for seed oils, through them we're eating such a ridiculous amounts of PUFA; something that would be quite impossible in the ancestral environment. How can our bodies possibly be adapted to cope with that?

The consequence of this is that none of... (read more)

By what mechanism could natural selection have optimised our diets? Why should we expect long-tenured features of our diet to be necessarily healthy? We have consumed alcohol since long before we were modern humans, as one obvious counter-example to this sort of argument.
Saturated fats are definitely manageable in small amounts. For most of history, and still in many places today, the biggest concern for an infant was getting sufficient calories, and saturated fat is a great choice for that. When you look at modern hunter-gatherer diets, they contain animal products, but in most cases they do not make up the majority of calories (exceptions usually involve lots of seafood), the meats are wild and therefore fairly lean, and BMI stays generally quite low. Under those conditions, heart disease risk is small and whether it is slightly increased by the saturated fat in one's diet is mostly irrelevant. There is a big difference between chasing down the occasional antelope and pulling up to the drive through for a cheeseburger. So the evolutionary argument really is not strong evidence that saturated fats are harmless. I agree that the studies we have are mostly inadequate, but I don't think using hunter-gatherer diets as a control would be very useful either. If you change everything at once, you can't isolate specific causal factors. What we really need (but can't have) is a bunch of large scale trials that have many groups with many different interventions and combinations of interventions, and statistical power to distinguish outcomes between each group.
I think there's a few issues with this reasoning. For one thing, evolution wasn't really optimizing for the health of people around the age where people usually start having heart attacks. There wasn't a lot of selection pressure to make tradeoffs ensuring the health of people 20+ years after sexual maturity. Another point is that animal sources of food represented a relatively small percentage of what we ate throughout our evolutionary history. We mostly ate plants, things like fruits and tubers. Of the groups who's diets consisted of mostly meat, there is evidence of health issues resulting. The nutritional profile of breast milk is intended for a human who is growing extremely quickly, not for long term consumption by an adult. Very different nutritional needs. I believe mainstream nutrition advises against consuming refined oils, including seed oils . I may be missing a point you're making.
AFAIK, analysis of paleolithic diets is that there were a range of things depending on availability and some groups were indeed pretty high on animal protein. We don't have differential analysis of the resulting health, but I just wanted to point out that the trope of 'trad diets were low protein' is not super well supported. Trad diets were mostly lower fat does have some support, as raising very fatty, sedentary animals is more recent, and accelerated a bunch in the last hundred years. Although the connection between higher fat diets and negative health outcomes is then another inferential step that hasn't been strongly supported and is, AFAIK, somewhat genetically mediated (some people/groups do much better on high fat diets than others in terms of blood lipid profiles).
I don't know enough to dispute the ratios of animal products eaten by people in the paleolithic era, but it's still certainly true that throughout our evolutionary history plants made up the vast majority of our diets. The introduction of animal products representing a significant part of our diet is relatively recent thing. The fact that fairly recently in our evolutionary history humans adapted to be able to exploit the energy and nutrition content of animal products well enough to get past reproductive age, is by no means overwhelming evidence that saturated fats "can't possibly be bad for you". How would you define strongly supported? There is archeological evidence of Arctic people's subsisting on meat showing atherosclerosis.
If some some pre-modern hominids ate high animal diets, and some populations of humans did, and that continued through history, I wouldn't call that relatively recent. I'm not the same person making the claim that there is overwhelming evidence that saturated fats can't possibly be bad for you. I'm making a much more restricted claim.
I am perhaps not speaking as precisely as I should be. I appreciate your comments. I believe it's correct to say that if you consider all of the food/energy we consumed in the past 50+ million years, it's virtually all plants. The past 2-2.5 million years had us introducing more animal products to greater or lesser extents. Some were able to subsist on mostly animal products. Some consumed them very rarely. In that sense it is a relatively recent introduction. My main point is that given our evolutionary history, the idea that plants would be healthier for us than animal products when we have both in abundance, and the idea that plants are more suitable to maintaining health long past reproductive age, aren't immediately/obviously unreasonable ideas.

Thanks for writing this!

Typos & edit suggestions, for the post at, not in order: (feel free to ignore)

Stephan Guyunet -> Stephan Guyenet

The fourth mechanism is saturated fat free radicals. -> saturated fat causing / producing free radicals (?)

When humans build complex systems we modularize, -> systems, we modularize

That might suggest that that seed oils -> That might suggest that seed oils

Had cholesterol that looked slightly better by most measures -> Had cholesterol that looked slightly better by most measures.

I don’t see

... (read more)
Many thanks! All fixed (except one that I prefer the old way.)

Once you start adding chemistry, things can get weird fast.  For example, a particular class of antibiotics may be behind the boost in diabetes in the US:

Seed oils are usually solvent extracted, which makes me wonder, how thoroughly are they scrubbed of solvent, what stuff in the solvent is absorbed into the oil (also an effective solvent for various things), etc

Glyphosate for dessication is kind of horrifying, I'm surprised I didn't know about it, but this explains a lot.

Basically all fish in the USA should on... (read more)

  I looked into this briefly at least for canola oil. There, the typical solvent is hexane. And some hexane does indeed appear to make it into the canola oil that we eat. But hexane apparently has very low toxicity, and—more importantly—the hexane that we get from all food sources apparently makes up less than 2% of our total hexane intake! Mostly we get hexane from gasoline fumes, so if hexane is a problem, it's very hard to see how to pin the blame on canola oil.
3RedMan more recent source on hexane tox.   I'm not just talking about the hexane (which isn't usually standardized enough to generalize about), I'm talking about any weird crap on the seed, in the hopper, in the hexane, or accumulated in the process machinery.  Hexane dissolves stuff, oil dissolves stuff, and the steam used to crash the hexane out of the oil also dissolves stuff, and by the way, the whole process is high temp and pressure. There's a ton of batch to batch variability and opportunity to introduce chemistry you wouldn't want in your body which just isn't present with "I squeezed some olives between two giant rocks" By your logic, extra virgin olive oil is a waste, just use the olive pomace oil, it's the same stuff, and the solvent extraction vs mechanical pressing just doesn't matter.
Strong upvoted. I learned a lot. Seriously interested in what you think is relatively safe and not extremely expensive or difficult to acquire. Some candidates I thought of but im not exactly well informed: -- Grass fed beef -- oysters/muscles -- some whole grains? which? -- fruit -- vegetables you somehow know arent contaminated by anti-pest chemicals? I really need some guidance here.
Unfortunately, I haven't found a solution that scales, and I don't think there is one. I suspect that a clean environment is incompatible with most technological infrastructure.  Microplastics, oilfield brines, combustion products, industrial/agricultural/mining waste, etc all accumulate in the environment and concentrate on the way up the food chain. Even a strip mall generates a ton of pollution in the nearby water table. I've given up on 'pure' and just try to have a clear understanding of how I'm poisoning myself.  The most depressing thing about this is that I've been to absolutely beautiful farms, with happy animals...and in my due diligence discovered that the reason it was affordable to homestead there is because the textile plant closed in the 70s, so all the jobs left...but the PFOAs stuck around. So... I try to know what's going into my body, avoid poison where possible, and do my best to get whatever garbage is accumulating out. That being said, I think the stuff that has done the most damage to my body are medical products.  Read those labels carefully!

I've been doing my own seed oil / obesity investigation for several months now, and I must commend this post for covering all of the major points. My only gripe is that I believe most meta-analyses are wrong because they don't weed out the bad studies (e.g. ones that are poorly designed from the outset or that mistakenly confound their analysis by, say, lumping omega-3 and omega-6 PUFAs together). I imagine the meta-analysts would want to remove these problematic studies so I understand that there are limits to what can be measured.

I posted a comment simil... (read more)

The other major question I'm grappling with is why there is an obesity-elevation gradient.


A guy is going alone through the wilderness, with a solar powered icebox on his back. He crosses a raging river by swimming. He slashes his way through a jungle. He is blasted by sun on an endless desert. It's been weeks and he has no company at all, save the bleached bones (and ice boxes) of those who did not make it. He climbs a mountain until he finally comes to a cave in the snow. Inside is a man with beard like silvery horsehair, eyes like fire. Very old but fit as a mountain goat.

"O wise sensei, I brought your pizza and ice cream with me. Now tell me the secret of perfect health!"

"It is vely simple", says the old man while greedily unwrapping a stick of icecream. "Only meet with people who have made a journey such as you youlself just did."

More prosaically: "It" does not run uphill.

~90% of Earth's mammalian excreta is produced by humans and their livestock. The livestock especially are immobilized in close quarters and their manure is spread to fields by mechanical means. The manure is often in a fresh condition with viable gut flora present. This means that the fitness of the gut ... (read more)

If you want to be healthier, we know ways you can change your diet that will help: Increase your overall diet “quality”. Eat lots of fruits and vegetables. Avoid processed food. Especially avoid processed meats. Eat food with low caloric density. Avoid added sugar. Avoid alcohol. Avoid processed food.

I'm confused - why are you so confident that we should avoid processed food. Isn't the whole point of your post that we don't know whether processed oil is bad for you? Where's the overwhelming evidence that processed food in general is bad?

I think we're pretty confident that refined oils are unhealthy (especially in larger quantities) , I believe there's just controversy about the magnitude of explanatory power given to seed oils.

See also Adam Ragusea's podcast episode on the topic.

Thanks a lot for countering the misinformation online.

After YouTube promoters got bored from the keto and low-carb wave (even though all dietary guidelines, plus associations like the American Heart Association, recommend consumption of complex grains and complex carbohydrates from fruits and vegetables), YouTube promoters had to find something new to assign the blame on.

Vegetable oils, and the derogatory term they assigned to it (“seed oils”), became the new target 🎯 Some within the same group even turned it up a notch and started suggesting eating only... (read more)

the thing that every expert screams every time they have a chance—AVOID PROCESSED FOOD.

The USDA defines processing as:

washing, cleaning, milling, cutting, chopping, heating, pasteurizing, blanching, cooking, canning, freezing, drying, dehydrating, mixing, or other procedures that alter the food from its natural state. This may include the addition of other ingredients to the food, such as preservatives, flavors, nutrients and other food additives or substances approved for use in food products, such as salt, sugars and fats.

Basically, don’t do… anything?

I ... (read more)

Bread is ultra-processed? O_O
6Said Achmiz
I think “packaged bread and other bakery products” this is referring to stuff like Wonder bread, which contains a whole bunch of stuff[1] beyond the proverbial “flour, water, yeast, salt” that goes into homemade or artisanal-bakery bread. ---------------------------------------- 1. Soybean oil, high fructose corn syrup, various preservatives, etc. ↩︎
Yeah, I did some Googling and packaged supermarket bread has all kinds of stuff added to it. (There's a reason the bagels from the bagel store nearby get moldy and the "Thomas's Bagels" from the supermarket last forever...)
Most bread you would buy in the supermarket is ultra-processed (including almost all organic, whole grain etc etc).  Types of bread that are only -processed- (not ultra processed): - Bakery-made bread, often sourdough, with an ingredients list that looks like (wheat flour, salt, water) perhaps with additions like fruit or seeds. This sort of bread lasts a couple of days at best. - Bread made from literal whole grains--German fitness bread, pumpernickel, sunflower seed bread. This stuff. It is shelf stable but tastes more like a solid cracker than normal bread. - Anything you make yourself at home. That's it. Anything with preservatives, dough thickeners, soy lecithin etc in its ingredients list is ultra-processed.
2Said Achmiz
Unless you freeze it. This is by far the best way of consistently having not-ultra-processed bread that tastes fresh and delicious, without having to eat a whole loaf every day or throwing away most of it. EDIT: This also works for various sorts of buns, rolls, panettone, etc.

I understand this really well written text is a deep dive into Seed Oils, but there is a crossing issue that's not mentioned thought: how does the use of pesticides and synthetic fertilizers?

It seems to me quite relevant as both canola and soy, the top 2 growers in consumption, rely heavily on those aids, which have grown in use and complexity.

"Processed" is a political category, not a nutritional one. I suspect that "ultra-processed" was invented because the literal meaning of "processed" was too blatantly at variance with the political job required of it.

"Political category" seems, a bit strong? Like, sure, the literal meaning of "processed" is not what people are trying to get at. But, clearly, "those processing steps that are done today in the food production process which were not done N years ago" is a thing we can talk about. (by "processing step" I do not include things like "cleaning the equipment", just steps which are intended to modify the ingredients in some particular way. So, things like, hydrogenation. This also shall not be construed as indicating that I think all steps that were done N years ago were better than steps done today.)

But for anything that’s been studied in detail, there’s always lots of evidence to support any semi-plausible view. Do you have any idea how much evidence people can produce for UFOs or chronic Lyme or colloidal silver?

To me, the colloidal silver situation feels strange. It seems that it was used as an antibiotic in the past but we don't have good studies that tell us whether or not it works as an antibiotic. If there would be good evidence that it doesn't work it would likely be on the Wikipedia page.

Health authorities warn about the dangers of antibiotic... (read more)

The obvious thought is that it is total fat consumption that is at least one of the contributory factors in the rising obesity crisis. The fact that the relative percentages of saturated fat to unsaturated consumed today has changed is possibly a red herring. The rise in total fat consumption is clear. 

Unclear. High fat and high carb diets have been directly compared and not found to be a smoking gun.

This was a great post, really appreciate the summary and analysis! And yeah, no one should have high certainty about nutritional questions this complicated.

For myself, I mostly eliminated these oils from my diet about 4 years ago, along with reducing industrially-processed food in general. Not 100%, I'm not a purist, but other than some occasional sunflower oil none of these are in foods I keep at home, and I only eat anywhere else 0-2 times per week.  I did lose a little weight in the beginning, maybe 10 lbs, but then stabilized. But what I have most... (read more)

The LessWrong Review runs every year to select the posts that have most stood the test of time. This post is not yet eligible for review, but will be at the end of 2025. The top fifty or so posts are featured prominently on the site throughout the year. Will this post make the top fifty?

Just wanted to say thank you for this post! It changed my mind slightly (to considering seed oils potentially nonproblematic in and of themselves, outside their being incorporated into ultra-processed food). I appreciate that because it's a topic I care a lot about.

Traditional oils involve some processing, but they’re pretty easy. To make butter, you milk a cow and churn the milk. To make olive oil, you grind some olives and press them. To make lard, you take a beautiful pig with hopes and dreams, you kill it, you cut off the fattiest bits, and then you boil them and strain.

But here’s how you make canola oil: Take rapeseeds, put them through a vibrating sieve, then a roller mill, then a screw press, then do a hexane extraction, then do a sodium hydroxide wash in a centrifuge, then cool and filter out wax, then pass t

... (read more)

Most sources that I read often refer to this overfeeding trial of extra 1000 kcal of saturated (SAT), unsaturated (UNSAT) or carbohydrates (CARBS). Not that many people involved (38), but a good thing is that it is a controlled randomized trial where participants were given the food. Endpoints measured are liver fat content change via two pathways. So not an serious event like CVD or stroke, but a marker (fatty liver) that is easier to measure and an endpoint that we know that is really bad for health. Results: overfeeding with SAT is most harmful, more th... (read more)

Probably you should avoid "washed" food because if it has not been washed right now, fungi and bacteria are developing on it more rapidly profiting from the moisture. (I am thinking, in particular, about packets with micro-greens / leaves /..., which you can "simply put on your plate". I once found bits of wet grit (?) in one. Not buying them anymore.)


We eat too much, that's all. if you only do "breakfast + lunch, no snacks, no extra butter", it should be enough to have your BMI <25. 

I am an asian european with quite healthy habit, but even with all of that , I find it impossible to get the BMI below 25. It's always somewhere between 26 and 29. That is until COVID happens and I started experimenting a new type of diet: only eating lunch, no dinner. 

I skipped dinner for a year and got my BMI from 29 to 23. 

I finally realize how utterly stupid the whole concept of dinner is. I mean, who ... (read more)

The problem with routinely skipping dinner is getting enough protein. No matter how much protein you eat in one sitting, your body can use at most 40 or 45 grams. (The rest is converted to fuel -- glucose, fructose or fatty acids, I don't know which.) On a low protein diet, it is difficult to maintain anything near an optimal amount of muscle mass (even if you train regularly with weights) -- and the older you get, the harder it gets. One thing muscle mass is good for is smoothing out spikes in blood glucose: the muscles remove glucose from the blood and store it. Muscle also protects you from injury. Also men report that people (men and women) seem to like them better when they have more muscles (within reason). But yeah, if you don't have to worry about maintaining muscle mass, routinely skipping meals ("time-restricted eating") is a very easy way to maintain a healthy BMI.
As a counterpoint, take a look at this article: The upshot is that the studies saying your body can only use 45g of protein per meal for muscle synthesis are mostly based on fast-acting whey protein shakes. Stretching out the duration of protein metabolism (by switching protein sources and/or combining it with other foods in a gradually-digested meal) can mitigate the problem quite a bit.
The problem with too-hungry people is that yes, they eat too much, and no, they cannot just stop. The way it works is so: they eat a meal, start feeling very hungry an hour later, make an effort and resist eating for another hour, then some more until they can't anymore and they give in and gobble up everything in the fridge. In cases like this skipping dinner is not actually possible, at least long-term.
Eating a meal does not immediately increase the available amount of energy. After eating a meal the body has to first spent hours on processing the meal before the energy is available.  If a hunter goes for a hunting trip they are usually eating the food after they did their hunting and not before starting their hunting trip. Our body is not optimized to at the same time sending a lot of blood to the intestines to gather resources and send the blood to the muscles for performance. 
FWIW I normally eat dinner around 6, go to bed 5 hours later at 11pm, and eat my next meal 8.5 hours later at 7:30am; at which point "break-fast" is certainly the right word, since I haven't eaten for 13 hours.  Contrast to breakfast, which only has to last me 5 hours (until lunch at 12:30pm), and lunch which again only has to last me 5.5 hours (until 6pm).