[bluGill]

In my youth it was assumed that the problem with fats is when they were solid at room temperature. Thus saturated fat was assumed to have the same effect as much cheaper trans fat, so they studied trans fat and called saturated fat bad. Then someone else recommended margarine (transfat) over butter because the headline said saturated fat (and the article may not have even mentioned they actually tested trans fat because there was thought to be no difference)

Some of this was science not knowing they needed to check things, but a lot of it was media and industry groups trying to sell a product and running a with half truths that fit their narrative. there are a lot of old studies that we cannot/should not reference today at all because things we now know are important were not something science took care to control for.

Problem is good science takes years. Health authorities need to make recommendations today, and often for political reasons don't get the option to say I don't know.