exercise, routine of daily meals, content of meals, amount of calories consumed as opposed to those expended
All people have different rates of metabolism at various periods of their lives. Younger people typically have higher rates, which is why they seem to eat a whole lot of food yet remain slim and trim. The metabolism rate accounts for the number of calories they burn, and the number of calories taken in, as opposed to the number expended, determines if they gain or lose weight. As a person ages, his rate of metabolism typically slows down, and the person might put on weight even though he is not overeating, due to a slower rate of metabolism.