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...
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 :-)
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.
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. skimming quickly through, here are a few phrases that stand out as "I'm too chicken for that":
"There’s no data for Antarctica because all the people there are penguins."
"To make olive oil, you grind some olives and press them."
"Lots of trials where vegetable oils look great were also excluded."
the middle quote strikes me as a paradigmatic example of what happens when you take all the most standard writing advice i know of and apply it without tripping over your own damn feet. "To make olive oil, you grind some olives and press them." even though i love reading it, when i imagine writing it, i feel so scared of everything i'm lea...
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.
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 option: almost all middle-class households buy one a day at least.
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.
Curated.
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.
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...
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.
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...
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?
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):
https://dasher.wustl.edu/bio5357/readings/naturerevmcb-19-281-18.pdf "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...
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...
Thanks for writing this!
Typos & edit suggestions, for the post at dynomight.net, 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
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?
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: https://pubmed.ncbi.nlm.nih.gov/24947193
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...
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...
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 ...
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...
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 ...
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.
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...
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.
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...
PUFAs absorbed by human monogastric digestive system. Where else does this highly liquid-like body fat in humans come from if not our diet?
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.
Hopefully, the review is better than karma at judging enduring value. If we have accurate prediction markets on the review results, maybe we can have better incentives on LessWrong today. 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
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...
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 ...
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:
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:
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:
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 and hydrogen atoms linked together with a couple oxygen atoms near the end. 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):
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:
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:
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:
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:
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.![](https://dynomight.net/img/seed-oil/world-obesity.png)
(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:![](https://dynomight.net/img/seed-oil/world-omega-6.png)
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.