Although one of every two American adults is presently following a restricted calorie diet, almost 75 percent of us are overweight and the obesity epidemic continues to expand. Certainly, overeating and underexercising are part of the problem, but the underlying cause of progressive weight gain is more basic and less understood.

Let's examine the three-step process responsible for much of the weight gain we experience on a year to year basis. First, with the exception of those who do regular strength exercise, adults lose about one-half pound of muscle tissue every year. Second, this annual muscle loss causes about a one-half percent reduction in resting metabolism every year. Third, the reduced calorie requirements result in approximately a one and one-half pound fat gain every year. While this process may not seem to be very important in the short term, it leads to serious consequences in the long run.

Consider that between the ages of 20 and 50, the average American woman loses 15 pounds of muscle and adds 45 pounds of fat, for a 60-pound change in her body composition, physical condition and personal appearance. Unfortunately, dieting will not prevent the progressive loss of muscle tissue and the resulting reduction in resting metabolism. Neither will endurance exercise such as walking, jogging or cycling, as good as these aerobic activities are for cardiovascular health.

The best thing adults can do to prevent or reverse the pervasive problem of muscle loss and metabolic slowdown is regular participation in strength exercise. If there is one physical activity that men and women should take the time and effort to do, it is sensible strength training. They may be surprised to learn that the most effective programs of strength exercise use basic and brief training protocols. Research clearly shows that properly performed 20-minute strength training sessions can produce better results than less focused weight workouts lasting 60 to 90 minutes.

Unlike endurance training, which is based on the exercise duration, strength training is based on the exercise intensity. In other words, people don't have to do a lot of strength exercise as long as they do it properly. Over the past 15 years, the South Shore YMCA weight loss program participants have experienced excellent results by performing one good set of 12 basic strength exercises, two or three days per week. They use a moderate weightload that they can lift at least eight times with correct technique. When they complete 12 good repetitions the resistance is increased slightly to facilitate further muscle stimulus and continued improvement.

After just two months of training, more than 2800 program participants averaged about three pounds more muscle which recharged their resting metabolism by more than six percent. Those who did not diet lost about four and one-half pounds of fat, while those who followed a sensible nutrition plan (modified USDA Food Guide Pyramid) lost about nine pounds of fat. Although adding three pounds of muscle and losing nine pounds of fat shows only a six-pound weight loss on the bathroom scale, it really represents a 12-pound improvement in body composition, which is pretty impressive.

Many fitness experts believe that muscle strength is the most important component of physical fitness, because muscles are the engines of our bodies. However, most successful weight loss/fitness programs also include aerobic activities (treadmill walking/jogging, recumbent cycling, etc.) for increased cardiovascular endurance, and stretching exercises for enhanced joint flexibility. Research indicates that well-rounded fitness programs are preferable from a total health perspective, so adults are well-advised to complement their strength training with some aerobic activity and stretching exercise. Of course, more total physical activity means more total calories burned, which accelerates fat loss.

Dieting can also increase the rate of fat loss, but people who cut calories without strength training typically lose muscle as well as fat. Approximately 25 percent of the weight lost on low-calorie diet plans is muscle tissue, which sharply reduces resting metabolism and makes it very difficult to keep the weight off. This is why more than 90 percent of successful dieters regain all the weight they lost within one year. Don't let your clients be fooled by popular diet plans that promise rapid weight loss but do more harm than good in the process, and make it nearly impossible to maintain an ideal bodyweight, let alone a desirable body composition.

For best results in terms of fat loss, muscle gain and physical appearance have your clients combine a basic exercise program (e.g., 20 minutes strength training, 20 minutes aerobic activity, and 5 minutes stretching performed three non-consecutive days per week) with a sensible nutrition plan (e.g., modified USDA Food Guide Pyramid).