Reduced muscle mass includes skeletal muscle, smooth muscle and muscle that affects vital organ function, with loss of cardiac muscle perhaps the most important. Cardiac capacity can be reduced and cardiac function impaired by chronic diseases such as athero-sclerosis, hypertension or diabetes. Changes also occur in the kidneys, lungs and liver, and in our ability to generate new protein tissue. In addition, aging can slow the immune system's response in making antibodies. The most significant result of the loss of lean body mass may be the decrease in basal energy metabolism.
Metabolic rate declines proportionately with the decline in total protein tissue.
To avoid gaining weight, we must reduce calorie intake or increase activity. The goal is energy balance. Total body fat typically increases with age. This often can be explained by too many calories. As we age, fat tends to concentrate in the trunk and as fat deposits around the vital organs.