We can't experiment directly on humans - we can only look for correlations, which always causes trouble with determining causality. Biological questions are inherently complicated, so any hypothesis is necessarily little more than a stab in the dark, even if we had the ability to compensate for genetic variation et cetera, which we most certainly don't. Large-scale studies are expensive, time-consuming, difficult to organize, and would inevitably end up politicized from 200 different directions, and then driven into the ground in the next campaign season.

In short, any and all dietary studies are doomed to be 99% failures.

But that 1% is important. I don't think there's much question that we have a better understanding today, of what constitutes healthy food, than we did 50 years ago. We know, in particular, that foods rich in certain substances (I don't want to try to classify them all in one or two words, because I don't study this stuff and would get it wrong - I'm talking about tradition "junk foods" and sweets, like cupcakes and potato chips.), are strongly correlated with a wide variety of health issues, the incidence of which has increased over the last several decades. Furthermore, these foods are inherently attractive to children, and (perhaps more controversially?) display limited addictive properties.

Yeah, our knowledge is limited, and yeah, we'll have missteps. But I don't think this is "premature optimization" - the program's running really slowly, and everyone's complaining about it. We don't understand a lot of why it takes so long to finish, but there is something we can do that would probably make it at least 5% faster. Why not give it a shot, and then go back to profiling?

Oh, and have an upvote, for contributing to the conversation. Because that's the etiquette around here, although some seem to have forgotten.

It is quite valid - if we have a strong suspicion on something, it could be helpful to give a shot.

I'm just concerned we don't know how strong our suspicion is, which turns that into a bet (more on that later)

The real problem IMHO is that this bet will certainly prevent or stall proper studies for a long time afterwards.

Take for example LSD - there are many results suggesting it might be effective on depression. Yet it was banned, which means once we have the technology to conduct a real large scale study, we may not have enough data points as we would have if it had not been banned (thanks to recreational users)

I mean, it is not ethical to willfully expose human to known dangerous drugs, yet if they take it wilfully by themselves or by mistake, it's a great source of data: for example, pharmacovigilence collects accidental use of drugs by pregnant mothers to guesstimate the toxicity on the fetus or the LD50 on humans)

This is just an example, but you can see how it might scale, basically we are taking bets, and it hampers research.

Also, it is quite philosophical. Personally, I'm against coffee due to its addictive potential and it's social image, yet it would be wrong for me to say there are no positive outcomes linked to it, or that on average it might have positive health benefit. I just don't know. There are many contradictions and I remember reading an article on how there seems to be time trends in negative or positive studies result, with an oscillation. (which would suggest that our research results are biaised by our perception)

An outright ban on caffeine, like on LSD, even if it might be a) coherent with my refusal, and b) more comfortable to me since I know I wouldn't be accidentally exposed to coffee (ex: in a soda), would certainly hamper further research, which would be detrimental if there was after all a positive health benefit on average - ie it would deprive me of future data which could help me change my mind.

IMHO, with bad data, taking bet with one's health is acceptable (if at no cost for the health system). Taking bets with the other people health - aka banning or mandating, is wrong.

EDIT: I just noticed your answer. Sorry if I improperly stated my intend. The goal was not to enter into a philosophical debate, but to have counter arguments. I am interested in either proving or disproving my thoughts - both are fine. Therefore, to avoid sparking a debate, I will not reply to your comment. Your answer however was very helpful and helped me clarify my thoughts. I agree with your points. Thanks a lot, thanks also for telling me your position and your data on coffee. For my position on coffee, see https://news.ycombinator.com/item?id=5632696 and https://news.ycombinator.com/item?id=5632995 - I'd rather not say more, or a coffee fanboy may start a debate.

> I mean, it is not ethical to willfully expose human to known dangerous drugs, yet if they take it wilfully by themselves or by mistake, it's a great source of data: for example, pharmacovigilence collects accidental use of drugs by pregnant mothers to guesstimate the toxicity on the fetus or the LD50 on humans)

The issue at hand isn't the subject's consent, I assume - the issue is our act of encouraging an individual to do something that might be harmful. Otherwise, there would be nothing wrong with performing studies on heroin use, as long as the appropriate warning labels were affixed. (I'm just assuming you're not a hard-core libertarian. If you are: just have a private company enforce the ban, and all will be well ;P )

I think, though, that it's also unethical to allow /others/ to knowingly encourage an individual to do something harmful. I recognize this is pretty controversial (if I were religious, I'd be a pain in the ass), but it means that if we are reasonably certain that item X is harmful, banning or restricting advertising is a must.

I also think it's ethically preferred to, where feasible act to discourage others (without coercion) from doing things harmful to themselves. Government- and charity-run nutrition programs, PSAs, etc.

That's our ethical dilemma, I guess, or at least mine. On the one hand, long-term scientific knowledge may be more rich and valuable if nothing is done. On the other, there is a moral imperative to take actions which might limit that long-term knowledge.

I'm inclined to assert, boldly and without factual basis, that there will be "enough" people who disregard the advertisements and PSAs, that scientists won't be much bothered by the missing data. Remember it's not like LSD; we're not banning the substance, just the encouragement. People smoke plenty of cigs, even though they're not advertised (and there's abundant negative advertising).

(By the way, I'm also very against coffee, having bad personal experiences with an individual who's behavior was/is noticeably negatively affected by the stuff. I'd support normalizing drug laws by lumping hyper-junk foods, caffeine, alcohol, cigs, pot, and other mildly harmful items of varying addictiveness into one big "restricted advertising" category, and using the taxes to send out occasional PSAs.)

And the first two paragraphs of your comment read like a conspiracy nut's rant. It significantly lowers your credibility and quite justifies downvoting you for making assertions that contradict scientific consensus without providing any supporting evidence.

Because it is killing people

Basically, at the moment we don't know for sure what's best, and we can't.

We may not know what is best, but we do know some things that are extremely harmful.

We know that eating extremely calorie-dense foods is a contributing factor to obesity. Beside the many studies that show this (which may or may not meet your somewhat unusual standards) we can rely on chemistry and biology.

It's easy to calculate how many calories someone eats based on their diet. It's easy to calculate how many calories they burn based on their lifestyle.

If the amount they eat is in excess of what they burn, they gain weight. In children some of that goes towards growing, but it's easy to calculate that too based on average growth weights.

Yes. You don't need to look at the effects of a particular diet because you can be reductionist as a proxy. For example, examining the effect of a meat-heavy diet on people is difficult, as you said. But if you know what meat does in a diet (correlates with high cholesterol, e.g.) you can examine the effect of high cholesterol on a diet, and if you find out it's bad you could determine that eating in a way which contributes to high cholesterol is generally a bad idea.