> I consider it borderline immoral, given the type of affect this could have on people's behaviors, to assert a conclusion based on such poorly conducted research.
Based on the massive amount of evidence linking 'chemicals from plants' (polyphenols, glycosinolates and others) with (in the main) markedly positive effects on human biochemistry & physiology, this appears to be a very good idea.
It's noteworthy that the 'five (vegetables/fruit) a day' mantra is a familiar one in the UK and I guess elsewhere. But rarely does anyone explain precisely why this is a recommendation given that it's quite possible to supply the required fat, protein, carbohydrate, vitamins and minerals without consuming significant amounts of fresh fruit and vegetables (using supplements).
That particular behavioral change likely wouldn't be bad itself, but that was more a rant on these sorts of studies overall. Poor research has real world consequences in this case (nutrition research), and we really need sound insight into what diet works best for the individual.
Even after you control for all the things you propose controlling for, you still have a huge confounding factor in genetic makeup. So then you need prisons with thousands of identical twins, each pair living out the same life in all ways but diet (which is meticulously recorded).
You're just not going to get an experiment like you can lay out in physics.
I think the point of the author mentioning major limitations in the paper is to acknowledge that this is sadly the best we've got to work with
Oh, yeah, the biochemistry of individuals is what makes so especially challenging, but not insurmountable. Maybe we are in a simulation to find out whether eating fish is good for you...
> Poor research has real world consequences in this case (nutrition research), and we really need sound insight into what diet works best for the individual
I think your claim is unsubstantiated. You're for some reason under the belief that nutrition has a large impact on people's life expectancy and health, but I don't know what accurate experiment or data you're basing this off, while also pointing out that this research was not good enough.
All the nutrition studies are like this, and so if you disregard them, you're left with no reason to believe nutrition even affect health or life expectancy for the average person in the first place.
It's noteworthy that the 'five (vegetables/fruit) a day' mantra is a familiar one in the UK and I guess elsewhere. But rarely does anyone explain precisely why this is a recommendation given that it's quite possible to supply the required fat, protein, carbohydrate, vitamins and minerals without consuming significant amounts of fresh fruit and vegetables (using supplements).