[vkk8]

> As a layman non-scientist, I wonder why we see so many relatively low-value observational studies in diet/nutrition, often with results that get contradicted or fail to replicate a few years later.

On my peak fitness enthusiasm I kept a rigorous food diary for some time and it was such a pain in the ass that I don't believe for a second that food diaries coming from people who are not 100% committed and interested in keeping one are accurate at all. People would often forget to log small snacks they have, or estimate portion sizes completely wrong, or neglect logging sauces, oils, condiments, etc.