The science behind America's rate of obesity says that our rate of obesity is caused by the fact that we're consuming more energy than we burn. It can't be blamed on a macronutrient, a micronutrient, some food ingredient, or a chemical. Americans are consuming too much food and beverage while living a sedentary lifestyle.
Sugar makes you fat
Consuming more calories than you burn makes you fat. It's the amount of calories that matters, not the source of those calories.
“Consuming more calories than you burn makes you fat. It’s the amount of calories that matters, not the source of those calories.”
That is the dominant theory, but their are plenty of scientist who disagree with it.
The alternate theory is that fat accumulation is controlled by hormones. They have done many studies where they deliberately overfed volunteers, some people gained weight while other did not.
Certainly the way we consume carbohydrates (amount and concentration) is not natural. Where is the Pizza tree or the doughnut bush in nature