Q. How do people become overweight?
A. There are different explanations for why people are fat. Reasons include people's culture (like the foods people eat, and how active they are--like watching TV all the time vs. playing sports and playing oustide, or religious beliefs that tell you when to eat and when not to eat, like fasting). There are also body differences such as different metabolism rates and differences in the nervous system. People may also get fat from overeating or by eating lots of high fat or high calorie foods.
Silverstein V, Silverstein A and Silverstein R. So You Think You're Fat? New York: HarperCollins, 1991, pp. 54-78.