This is a recent problem. Do we think those purported fat genes just evolved in society over the past eightyish years, and spread so widely that, per the 2017-2018 NHANES data, 73% of American adults are overweight (30.7%) or obese (42.4%)? On a population level it’s clear this cannot be genetic. There’s been a cultural shift that has caused this problem, often thought to be related to processed food, less time to cook, and for some underserved communities, food deserts.
Look at how dramatically obesity has risen since the '80s:
Wait, what’s their true purpose?