Sisson is the guy behind the Primal diet, which is essentially a primer for Paleo (which is what I do with some modifications). I know of his stuff too, and even consume some of the stuff from Primal Kitchen at times.

many theories about what happened. most recently people try to attribute obesity epidemic to seed oils which are both an abundant calorie source, very new in human diet, and have some cannabinoid type activity that may make them addictive.

another factor could simply be social acceptance. a fat woman reported on Twitter that when she was in China she was called fat to her face. frankly 100 years ago a fat person anywhere would be called fat to their face. but now we are accepting of obesity the way we accept homosexuality etc.

i was beaten for being a fat kid in school in USSR. nobody was going to stop it. i had to learn about diet and exercise and lose weight - there was no other option. i was also facing mandatory military service as well, which was another reason to get in shape.

America has a disgusting food culture. I have never eaten in a car and never will. In Germany cars are sold without cupholders because only American swine eat in cars. I recently saw a boomer couple get into their car while both eating ice cream - i would have killed those pigs if i could.

i honestly don't think the obese people today are that way because they listened to the advice of dietitians and are having a protein bar every 2 hours. i don't think any obese person has ever eaten a protein bar in their life.