Body Fat and Age

With each decade above age 25, the body loses about 4% of its metabolically active cells, says Dr. Brian J. Sharkey in his book Fitness and Health. "If the diet remains relatively unchanged during a 10-year period, weight will be gained, since the total energy expenditure has declined. This means that the adult should either exercise more or eat less in order to maintain a desirable weight.
"Individuals who can claim that their weight has not changed since college should be congratulated," says Dr. Sharkey. "However, they should also know that the loss of metabolically active cells with age usually means a decline in lean body weight. Therefore, the maintenance of body weight usually indicates an increase in the percentage of body fat. Body weight alone is not sufficient evidence that you are winning the battle of the bulge."