There is no obvious causal mechanism, we always need a study. It's very easy to be biased (Just read a few of these articles for examples http://wiki.lesswrong.

There is no obvious causal mechanism, we always need a study. It's very easy to be biased (Just read a few of these articles for examples http://wiki.lesswrong.com/wiki/Sequences http://wiki.lesswrong.com/wiki/Sequences). Books like "wheat belly" and "Why we get fat?" make an alternative hypothesis to the commonly accepted "Saturated fat is bad"