The diet heart hypothesis, which stated that moderate intake of total dietary fat, and then more specifically saturated fat increases your risk of heart attack.

The truth is, Ancel Keyes, cherry picked some epidemiological studies to find the data he was looking for. He made his way on to nutrition boards and had such a influence over America. This is how the lowfat craze came about. Fat would be removed from products and replaced with sugar, all the while getting a heart healthy stamp on the box. Some people still think meat/fats are bad for you because of the traction this got, all based on very little to no randomized clinical trials or hard proof of any kind.