i used to follow ( and even once went to gym with ) a dude with PHD in biochemistry or something called Chris Masterjohn who had a podcast where he tore these studies apart.  there are some egregious things that take place in those studies - like having one group in a smoking building and another in a non-smoking building and then pretending like this has no effect of heart health and just focusing on difference in diet etc. 

 the point is design of a study is more important than results.

a study can always be designed to produce desired results.