Or are you wondering why you are gaining, even though you're not eating any more than you used to?

Here's the bad news: after age 40, the average person will lose about a half pound of muscle per year and replace it with a quarter pound of flab. During menopause, women will lose up to one pound of muscle a year and convert it directly into fat. This means that by age 55, the human body will burn about 600 calories less than it did at age 40. This explains why people find themselves eating less and less in order to maintain their current weight as they grow older.

Decreasing levels of lean muscle tissue and increasing levels of body fat mean more than just slow-motion metabolism. They also expose you to a greater risk of diabetes, heart disease, cognitive dysfunction, and depression.

The only truly effective and enduring way to combat this steady loss of muscle is with weight training and aerobic exercise.

Is More Exercise Really Better?

While it may be obvious that exercise is beneficial to good health, what may not be so evident is that more is not necessarily better. In fact, professional athletes or people who train intensively derive fewer health benefits from exercise than those who practice moderation.

Several recent studies have shown that as we grow older, just a little aerobic exercise can go a long way in conferring significant health benefits. In a recent NIH clinical trial, modest exercise, such as casual walking, was found to dramatically lower the risk of acquiring Type II diabetes, the leading cause of heart disease and the sixth leading cause of death in the U.S.

A University of Miami School of Medicine study also found that moderate exercise (such as walking) 5 to 7 times a week for 30 to 45 minutes delayed the onset of Type II diabetes in about 50 percent of susceptible individuals.

Moderate exercise can dramatically reduce chronic fatigue, according to a study published in the British Medical Journal (Fulcher et al., 1997).

Exercise can also improve cardiovascular health and relieve arthritis symptoms. A 10-year study of a group of 200 adults showed that walking 3 to 5 times a week was linked to an 86 percent reduction in heart disease (Pereira et al., 1998).

Just a short walk once a day can also reduce the odds of acquiring high blood pressure. According to a study published in the Annals of Internal Medicine, spending only 20 minutes or more walking to work was found to reduce the risk of hypertension by almost 30 percent.

Exercise can also produce stronger bones and reduce back pain. A 1996 Canadian clinical trial researched the effect of aerobic exercising for 90 minutes, 3 times a week, on bone density. At the conclusion of the study, the exercising group displayed noticeably stronger spines, reduced back pain, and a heightened sense of well-being compared with the non-exercising control group (Bravo et al., 1996).

The Hidden Benefit of Exercise - Better Sleep

The most powerful, but least known benefit of physical activity is that is promotes longer and deeper sleep - one of the cornerstones of longevity and good health (Kubitz et al., 1996). A Stanford University study concluded that only 30 minutes of exercise four times a week can help people over 50 fall asleep twice as fast and sleep an hour longer.