There are people who are fat, not because they eat a lot, but for example they suffer from some kind of illness.
The illness is eating too much of the wrong food, and indolence of course.
I visit McDonalds and Supermarkets a lot. When you see what people re buying and eating, it's pretty obvious why they are fat, and why they are turning healthy kids into obese unhealthy people with allergies and other problems.