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Comment by zhivota | Hacker News Reader

> This relationship remained significant when influences of caloric intake, urbanization, obesity, education and carbohydrate crops were statistically controlled.

In other words, they did not control for wealth or income, which quite obviously confound this entire exercise. Probably this paper is actively worse than useless.

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This is the problem with almost all nutritional studies. They’re almost always based on correlation. But human life has millions of facets, and each facet is correlated with thousands of other facets. It’s nearly impossible to discover a causal relationship between two lifestyle variables unless the effect is very pronounced.

So, we can't know trans fats are bad nor any other facts that you take for granted? What about smoking? I don't think people who say this realize the bullet they would have to bite. Though I only seem to hear it from people who are about to reject scientific consensus on something that's inconvenient for them because they like the taste of certain foods, like butter.

> It’s nearly impossible to discover a causal relationship between two lifestyle variables unless the effect is very pronounced.

Also, for many things (like smoking), we have established causal relationships by explaining the mechanism of action. E.g. cigarette smoke damages DNA, lead poisons the brain leading to neuron death, etc.

Also smoking has a large effect so you do notice it in every correlative study too.

The fact that you can pick up on negative effects through observational studies if they are large enough makes me especially suspicious about results that differ from study to study. Perhaps there is an effect there, but if we can't reliably pick up a signal, maybe it's not something I need to worry about.

What effect size is big enough for you to worry about? A quick google search shows that smoking reduces life expectancy by 5-13 years depending on the study. Let's say that for smoking, the 'true' reduction of life expectancy from smoking is somewhere in the middle, 9 years. Then, the study I found with the 5-year estimate, is wrong by 4 years.

So, for some lifestyle change to reliably be reproduced by observational studies, it would have to be a 'true effect' of 4 years. I would say that 3 years, or even 1 year, is something to worry about.

Oh no, the evidence is clear when it comes to smoking. What I was trying to say: Smoking is a nice reference point to orient yourself around, because you can fairly confidently conclude that it's very harmful even with imperfect methods. So we can pick up on large negative effects using imperfect tools. At the same time, when you apply the same imperfect methods to other objects of study (e.g. the impact of coffee on health), you often get much more inconclusive results, which change from study to study. In that case, I don't think there is much sense in worrying until more robust methods can find clear evidence.

Agreed.

You can’t prove a negative, but you can define limits on the effect size.

You can show that the maximum possible size effect size is so small that you’re not going to worry about it.

They take GDPPP and other factors into account, and further group countries by similar overall lifestyle e.g. Mediterranean countries.

I have not checked all the methods ,but I believe your criticism is to strong.

The paper is total garbage but they do put gdp in the specification. No one should take this “result” remotely seriously though.

Just out of curiosity, are you a vegan?

> education

Wouldn't this show up as a relation to education, since there's a very strong relation between education and income?

This thread is giving me Deja vu https://news.ycombinator.com/item?id=38830148

the real problem with these studies is the critics. If it's a study that says veganism is good, then everyone does that or has a moral imperative for that to be true will come out and say "what more do those evil meat eaters want?" while simultaneously the meat eaters will lambaste the study as worthless on any point they can find.

Of course, the situation works in reverse. The problem is that it's incredibly difficult to find genuine, unbiased, nuanced criticism of diet research. Some people are dumb enough to see research that actively admits to funding from some food industry and immediately they say "this study is total bullshit" which is just not how science works.

It's methodology sniping. Find some detail in the paper that looks wrong to laymen, then dismiss the whole study as trash.

Education is already a good proxy for income (thought they do take into account other criteria too for that).

It would be interesting to see stats on how education vs income relate to meat consumption, since education seems to also correlate with adhering to a plant-based diet by ethical choice (concern for climate or animal welfare).

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