Women and men store fat in different places. Men tend to carry weight on their chest, abdomens, and buttocks-they're "apples." Women, on the other hand, tend to carry fat on their breasts, hips, waists, and buttocks, making them "pears." The difference is determined by the hormones estrogen and testosterone at puberty. Puberty is also the time when the number of fat cells you'll have for the rest of your life is set. Fat cells are generated in the developing fetus and also at puberty, but normally aren't generated after that. When you store more fat, the fat cells increase in size, but not in number. (The exceptions are if you gain a large amount of weight or if you have liposuction.)