Obesity is sometimes uncontrollable. It's rare when the body doesn't send the signal that the stomach is full. In most cases, the person doesn't have the will power to eat less. It could be related to plain old gluttony and sometimes, it is related to a mental issue like using food as a way to comfort one's self from hurt.
I had this coworker who was 5'1' woman at a previous job. We all go out to eat and I end up driving her to the restaurant. When she got in my car, the passenger side dipped and stayed that way.

I don't know how much she weighed. But I've had passengers sit in and the right-side doesn't body roll. We get to the parking lot and there's a slight incline to walk from the parking lot into the restaurant. She had to take three breaks for the 40 foot walk to the door. It was more sad than funny. Think of a physically-fit person carrying a 275 lb. barbell plus plates for 40 feet. She had a skinny husband.