Fats in products were gradually replaced with sugars, so it really is cut and dry. It doesn’t imply that fats are healthy but obesity is exclusively carb related in the overwhelming majority.

Wrong. Americans are consuming more fat than ever, with the excess primarily coming from vegetable oils (soybean oil being #1):

https://www.vox.com/science-and-health/2017/2/2/14485226/ame...

https://www.ers.usda.gov/webdocs/charts/81355/December16_Fin...

Many Americans actually get between 10-20% of their daily calories from soybean oil alone.

And I get at least 50% of my calories from olive oil, and maybe a further 20% from cheese. Given that people from the US make up a little over 4% of the global population they’re not the measuring stick.

> Fats in products were gradually replaced with sugars

Let's experiment with that statement. Perhaps what I'm hypothesizing here is new, perhaps it isn't.

Don't take this as a position to argue with. I really don't have a dog in this fight.

Suppose that people have always been after a certain feeling of fullness, and this feeling is largely a product of evolution. It's also very emotion-driven, not purely physical.

When humans feel full, they stop eating. Of course it doesn't work perfectly, since we've always had fat people. It does happen to work for me and my extended family, since none of us have ever been obese.

Suppose that animal fats, being highly calorie-dense, give a feeling both of being full and being emotionally satisfying. Every chef will tell you that people love fat.

Now, if the food industry and nutrition scientists removed a lot of the animal fats, then both people's physical and emotional needs increased, and many searched for sugars and carbs to compensate. They are a poor substitute, though.

If this were true, then humans are getting more calories than they were when animal fats were a bigger part of the diet. It's not that animal fats are good for you as much as "if you don't consume them, you'll consume other things that are even worse."

Of course this is not a single factor to explain it all. A more sedentary lifestyle is also a big, big part of it.

>Now, if the food industry and nutrition scientists removed a lot of the animal fats, then both people's physical and emotional needs increased, and many searched for sugars and carbs to compensate. They are a poor substitute, though.

Anecdote. I've tested this personally and found it to be true. Gastric motility also increases with high animal fat diets, meaning on some level my body/brain feels like its getting what it requires faster.

I had to look that one up, although I had an idea :)