https://slatestarcodex.com/2020/03/10/for-then-against-high-saturated-fat-diets/

I.

In the 1800s, the average US man weighed about 155 lbs. Today, he weighs about 195. The change is even starker at the extremes. Someone at the 90th percentile of weight back then weighed about 185 lbs; today, he would weigh 320 lbs. Back then, about 1% of men were obese. Today, about 25% are.

This puts a lot of modern dietary advice into perspective. For example, lots of people think low-carb is the solution to everything. But people in the 1800s ate almost 50% more bread than we do today, and still had almost no obesity. Other people think paleo is the solution to everything, but Americans in the 1800s ate a diet heavy in bread, milk, potatoes, and vegetables, and relatively low in red meat and other more caveman-recognizable foods. Intermittent fasting – again, cool idea, but your great-grandfather wasn't doing that, and he had a 1% obesity risk.

This isn't to say those diets can't work. Just that if they work, they're hacks. They treat the symptoms, not the underlying problem. Something went terribly wrong in US nutrition between 1900 and today, and all this talk about low-carb and intermittent fasting and so on are skew to that thing. Given that 1800s Americans seem to have effortlessly maintained near-zero obesity rates while eating foods a lot like the ones we eat today, maybe we should stop trying to figure out what cavemen were doing, and start trying to figure out what Great-Grandpa was doing, which sounds a lot easier.