Controlling metabolism is one of the best ways to control weight. The key measurement is the basal metabolic rate (BMR) (the amount of calories the body requires at rest). The BMR consumption varies most with the pounds of muscle the body has.
Muscle loss begins after age 25 and averages about 0.5% annually without extra efforts. For every 10 pounds of muscle lost 600 less calories are needed but our appetites do not correspondingly decrease. Fat warehouses (cell) live on only 13 calories a day.
Replacing muscle of youth with fat is similar to hiring lazy employees in a business. Muscle loss reversal is possible with exercise and especially by moderate weight training. In multiple studies, short-term weight training in elderly men, even men over 80 years results in significant gains in strength and muscle mass.