Our diets changed. If we revert to eating what humans ate 100,000 years ago we do NOT need to count calories and we do not get fat. What happened is we started cooking and eating things that could not be eaten raw, like grains, potatoes and so on. If you eat only stuff that can be eaten raw your body will do a pretty good job of maintaining your ideal weight without counting calories (assuming you don't have a thyroid problem or something of course)
Looks like I am mistaken. We're taller than we have been for the past few hundred years, but there is evidence of some earlier humans having similar heights as modern humans. There is no mention of the cooked/raw status of those particular ancestors' diets, though.
I don't have a particular reference, just piecing together the non-trash results of googling 'diet height' and 'history of human height'.
We got the 'food pyramid' which told everyone that eating loads of carbs is good for you and eating fat in any form is bad. It's gonna take decades to reverse this mistake.
