[CTmystery]

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

[superqd]

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...