Weak evidence that eating vegetables makes you live longer

by jefftk3 min read10th Jun 201324 comments

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Personal Blog

People vary in how much they can taste bitter things. If you go around giving people the chemical Phenylthiocarbamide (PTC), which you shouldn't do, because it is toxic, you'll find that some people taste it as a strongly bitter while others can't taste it at all. Same with 6-n-propylthiouracil (PROP). While these aren't common in food, they're very similar to chemicals that are in a lot of foods, so you might think that how much you can taste PTC or PROP might influence what foods you like.

We can test this. Give people various foods that there is dispute about the bitterness of, and then compare their preferences to their sensitivity to PTC or PROP. Several studies have done this:

Vegetables like broccoli are often thought to be good for you, so shouldn't we expect to see people who taste PROP and PTC not live as long, because they're eating less of those? Ideally we would test how sensitive people are to bitterness at some youngish age, and then watch them for the next 80 years to see how long they lived. But 80 years is a long time to wait, and you're going to need a large sample because we don't expect the effect to be that big. Another option would be to measure sensitivity to bitterness, and see whether it decreased with age in the same way we would expect if the people with increased bitterness sensitivity were dying earlier. But this is going to be impractical to separate from the hypothesis that simply individual people lose some of their sense of taste over time.

Luckily, it turns out that this tasting ability is very strongly genetic. People with one variant of the gene TAS2R38 can nearly always taste PTC while people with another variant almost never can. So we can sample people at any age and get an estimate of how likely they were to have avoided vegetables for taste reasons. Are older people less likely to have the gene variant for tasting bitterness? It turns out they are. In Bitter Taste Receptor Polymorphisms and Human Aging (2012, n=941) they tested Calabrians for their bitterness gene variant, and did find that older people were less likely to have the variant for detecting bitterness:

So can we say that (a) eating vegetables will help you live longer and (b) if vegetables taste bitter to you should eat them anyway to get benefit (a)? Unfortunately it's not that clear. Vegetables aren't the only common food with these bitter compounds, so it might be something else. Other bitter-to-some foods that these non-bitter-tasters might have been eating more of include coffee, tea, grapefruit juice, soy, cigarettes (maybe), and probably other things we haven't tested. There's also the possibility that the older and younger participants in the longevity study aren't the same group of people genetically, and what they're actually capturing is population changes in Calabria. One way to test that would be to repeat the study in several different places, as we would expect population drift to be independent of sensitivity to bitterness.

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Taste and food preferences as predictors of dietary practices in young women (1999, n=157) found that "sensitivity to the bitter taste of PROP was associated with reduced preferences for Brussels sprouts, cabbage, spinach and coffee beverages". But it's behind a paywall, so this is just from the abstract

https://dl.dropboxusercontent.com/u/85192141/1999-drewnowski.pdf

One data point here: I think of myself as a subsupertaster-- most sensitivity to bitterness than most people, less than serious supertasters. I don't like grapefruit or coffee. I can sort of enjoy tea, especially the milder ones, but I don't get around to making it for myself. If I add enough milk and sugar to coffee to make it palatable, a cup gives me an upset stomach. I don't like the taste of alcohol. Does that go with being a supertaster?

On the other hand, I can handle most leafy green vegetables. When I was a kid, I didn't like endive, but I haven't had it for a while.

My tolerance for bitter flavors has increased over the years. I'm 60, and I'm not sure when the shift happened. Probably past age 40. I'm more tolerant of textures (like orange pulp in orange juice, or cooked raisins) that I hated when I was a kid.

I used to hate olives, but now I can handle most olives and rather like the mild ones.

I've also gotten used to peanuts and peanut butter.

Supertaster hell

My tolerance for bitter flavors has increased over the years.

Taste buds die as one ages. Try revisiting some foods.

What's with the formatting of that page? It insists on taking up most of the width of my screen. If I make it wider than about 3/4 of my screen, it makes the lines of texts longer to take up the extra space, but if I make the window smaller than about 3/4 of my screen, it keeps the lines the same length. and I have to scroll to see the whole thing.

Imagine the food you hate the most in the world. Now imagine that half the food in the world is made up of that food -- imagine there are whole restaurants dedicated to that food, that half the food available in any given restaurant is that food. Imagine you've spent your entire life being mocked and punished for not eating it because everyone else does. That is my world.

Huh.

In Bitter Taste Receptor Polymorphisms and Human Aging (2012, n=941) they tested Calabrians for their bitterness gene variant, and did find that older people were less likely to have the variant for detecting bitterness:

If you make claims like that, how about copying the p value from the article. A p value tell me more than your graph.

The chart shows the effect size, which is generally a better summary statistic. But if that's what you want, looking at the article again they say they found p<0.029.

Of course, one can come up with other hypotheses, such as that vegetables are bad for some people, and people with genes that make vegetables bad for them have evolved a sensitivity to them to warn them away, and so people who have a gene to warn them away from vegetables don't live as long, and will live even shorter if they eat lots of vegetables.

Neither hypothesis really makes much evolutionary sense, though. If vegetables are good for everyone, and there's a gene that discourages them from eating them, why hasn't this gene been selected out of the gene pool?

Modern vegetables are new on evolutionary timescales, because they've been bred for size. There may not have been time for human evolution to react.

I expect other pressures have changed, too. The first thing that comes to mind is that bitterness in plants is often a marker of toxicity; one of the steps in this quick and dirty edibity test for wild plants, for example, discards bitter ones. If a particular gene variant made a few harmless plants unpalatable but also made accidental poisonings less likely, I can see it being a net positive to foragers.

In an agricultural setting, where a few known-good plants make up most of the regular diet, the opposite might be true.

"Vegetables" is a very large class of food, most of the are sweetish (because of the starch), not many are bitter. You can eat lots of different vegetables without eating bitter ones.

I doubt the normal diet in Calabria includes a lot of Brussel sprouts or kale...

It might be useful to make a distinction between

  • Eating any vegetables at all
  • Not eating meat
  • Eating only vegetables

and other variants.

So there might be a statistically significant difference in lifespan between Coke drinkers and Pepsi drinkers.

Well Pepsi has a sweeter taste than Coke and Coke has a more bitter taste than Pepsi. So perhaps, by the reasoning in the article, people who prefer Coke are more likely to be the sort of people who enjoy eating vegetables. Or perhaps there is some other genetic difference between Coke preferers and Pepsi preferers which affects life expectancy.

Is Coke actually more bitter? I agree it's a bit less sweet. But I'm not sure that PTC-tasters and non-PTC-tasters experience Coke differently.

[-][anonymous]8y 0

Before reading the post, I thought the title would mean something like ‘the evidence that eating vegetables makes you live longer isn't as strong as you might think’.

Couldn't it be just that the variants of the gene contributes to shorter/longer lifespans regardless of food habits ? Or that the gene is more prevalent in certain ethnic groups who, for other reasons, don't live as long ?

Sure, it is weak evidence, in the sense that the hypothesis "eating more bitter vegetables makes you more healthy, but you don't it as much if you don't like the taste" predicts that correlation, but... it seems a bit far fetched to me to use a proxy like that gene, when we could directly monitor people's eating habits.

Any reason to use such an indirect approach (where the number of possible hypothesis is higher), instead of making direct correlations between eating habits and lifespan ? Is it easier to do, like because people can't lie about their genes but they can about their eating habits ?

"because people can't lie about their genes but they can about their eating habits"

That, and also that people are probably very unreliable about long-past eating habits even when not trying to lie about them.

I am not so sure about the tobacco case, anymore.

Still think that it's not very healthy, but a minor or bigger revision from the current official medical position wouldn't surprised me at all.

[-][anonymous]8y 1

There's decades of strong replicated research showing that smoking tobacco raises risk of multiple serious diseases and increases overall morbidity and mortality.

On the other hand, nicotine appears to be pretty close to harmless. The public health message is distorted in that respect.

Why? How did this post make you update in that direction?

Just too many medical revisions lately. Cholesterol, exercise, fat ...

Besides, I remember an UN study which claimed, that the passive smoking is more dangerous than smoking itself. Not very credible piece of work, I think.

Therefore, a minor revision is possible. Not necessary, but possible.

(I don't smoke, never did.)

Just too many medical revisions lately. Cholesterol, exercise, fat ...

There a huge financial interest into Cholesterol lowering drugs. There industry interest into people thinking Cholesterol is dangerous.

In the case of smoking it's very different. The doctors who find the link between smoking and lung cancer had to overcome a lot of resistance from well funded tabaco companies. There a lot of empirical data that shows that smoking is bad.

When it comes to exercise, exercise is complicated. There are many different ways to exercise.

On the topic of fat, it's hard to gather reliable data on what people eat.

Besides, I remember an UN study which claimed, that the passive smoking is more dangerous than smoking itself. Not very credible piece of work, I think.

If you think a particular study isn't credible it should influence what you believe one way or the other. Additionally it's good to link to studies you cite on lesswrong.

Therefore, a minor revision is possible. Not necessary, but possible.

Then which probability to you allocate to that possibility?