This is the question that the BBC experiment tries to answer. I recommend watching the whole documentary, but here’s a summary of the results:
This answers why some thin people have trouble getting fat. They ran an experiment with participants who are classified as thin, and asked them in a course of a few weeks to eat above average number of calories and not exercise.
All participants gained weight; but a lot of the participants had a hard time following the high-caloric diet. They had to essentially force themselves to eat, and some of the participants couldn’t eat the amount they were expected.
The reasons that thin people are thin and not fat fall into three categories:
- Regulation – Our bodies is internally calibrated to eat a certain amount of food/calories. Thin people have it calibrated lower.
- Metabolism – They didn’t focus on this very much but what’s interesting is that all the participants in the experiment gained fat (expected since they didn’t exercise), except for the single Asian male in the experiment, who gained muscle mass. Muscle mass increases the body’s metabolic rate so it helps keep you thin.
- Other – virus;