We now know that the average person’s lean body mass declines with age. As we progress from young adulthood into middle age, Americans tend to lose about 6.6 pounds of lean body mass each decade we live. After age 45, the rate of lean body mass loss accelerates.
According to William Evans and Irwin Rosenberg in their book, Biomarkers: The 10 Determinants of Aging You Can Control, “Muscle, to a far greater extent than most people realize, is responsible for the vitality of your whole physiological apparatus… We believe that building muscle in the elderly is the key to their rejuvenation.”
According to Evans and Rosenberg, a high ratio of muscle to fat on your body causes your metabolism to rise, meaning that you can more easily burn body fat and alter your body composition even further in favor of beneficial muscle tissue.