some fun study sort of concluded that the ratio carbs vs fat and protine is the entire mechanic. fat people who eat almost nothing eat only carbs thin people who can eat huge amounts every day eat a lot of fat and protein. Both eat other things just not as much.

I really eat a lot. When my gf cooked more and the potato meat ratio changed from 1:3 to 3:1 I immediately started to grow fat. I had her adjust it to 1:1 and started eating lots of sausages and chicken legs between meals. 500g to a kg per day worth of extra food. My body fat declined rapidly.