Women often gain proportionately more. The reason, however, is not an aging metabolism. One Criterion Energy requirement of muscle remains constant Exercise Physiology , the excellent textbook by Drs. There is probably no biologic reason for men and women to get fatter as they grow older. Increases in bodyfat, they explain, are more a function of activity than age.
Inactivity results in loss of muscle.
And loss of muscle, not an aging metabolism, is the primary cause of creeping obesity. The muscle that remains is as metabolically active as ever. Metabolism is the chemical and physical processes in the body that build and destroy tissue and release energy, thereby generating heat. Our metabolism speeds up when we exert ourselves, and we burn more calories. Our metabolism slows down when we are at rest, and we burn fewer calories.