It’s actually not. It’s got far more to do with the lack of satiation in our food and nutrient deficiency. 

Just having food around does not make a population naturally get really fat, and what we have today isn’t “normal fat” either, it’s specifically deficiency caused by bad oils and malnourishment. It causes us to aggressively over eat in a completely unnatural way because we get 100x the calories without the base oils, so we just keep eating and having to store away oxidized seed oil fats as fast as we can because they have nothing of value in them.