Some study shows that we don't know shit about diet:
https://time.com/5600706/personalized-diets-study/
Basically identical twins don't respond identically to the same food. At we can
guess it might be about gut bacteria -- which we admittedly know dick about. So there ya go.
Eat less calories eat less processed food seems to be the only thing we can agree upon besides "go out and try shit -- find something that works."