Dieting fails due to a combination of hormonal changes, muscle loss, and flat out frustration. When faced with a shortage of calories, your body's natural response is to conserve fat. This mechanism might have come in handy for our distant ancestors trying to survive a famine, but the "starvation response" and its associated hormonal changes make life difficult for many a dieter.

If a dieter persists long enough with the self-imposed famine, the body begins to break down muscle tissue for fuel. When that protein is broken down, it releases nitrogen. Your body will quickly wash away the nitrogen by releasing water from tissue cells, causing an immediate reduction in water weight and a noticeable drop on the scale. However, water and muscle loss is nothing to celebrate. The water weight will be quickly regained as soon as you have something to drink, and the missing muscle can wreak havoc on your metabolism for a good long time.

Muscle is a metabolically active tissue. It requires a certain number of calories each day to maintain it. Therefore, the more muscle you have, the more calories you burn even when you're just sitting around. As your muscle mass drops, so does your daily calorie requirement. Suppose, for example, that a dieter loses 10 pounds of muscle (along with maybe 20 lbs. of fat) on a strict diet. Now suppose that each pound of muscle had been burning 50 calories a day just sitting there. Together, those 10 pounds of muscle had been burning 500 calories a day. With this muscle tissue gone, the dieter must now consume 500 fewer calories a day in order to maintain that weight-loss.

However, we know that most dieters won't keep up the starvation routine for long. They'll eventually return to their old eating habits. When this happens, the weight inevitably comes piling back on. The kicker is that while they lost both muscle and fat during the diet, what they put back was all fat. So, even though they might weigh the same as they did when they started, they now have a lot more fat and a lot less muscle than they did before the diet. This means that their metabolisms are slower and their calorie requirements are lower. Even if they return to their pre-diet eating habits, they still require 500 fewer calories a day due to the muscle loss. That's one reason dieters are prone to regaining all of the lost weight and then some.

The solution to this dilemma is an active lifestyle that includes aerobic exercise, a weight-training program (pushing that lawnmower or digging that garden works as well as those bowflex machines), and a healthy diet. A healthy diet keeps your metabolism in high gear with 4 to 6 small meals a day. No food (as long as it isn't full of mycotoxins) is truly off-limits, but sweets and high-fat junk food should be eaten less often and in smaller quantities. A healthy diet is realistic and permanent; not something you suffer through for a week or two and then quit.

The goal is to consume as many calories as you can while still losing body fat and maintaining or gaining lean muscle. If your calories are already below normal, don't restrict them further. Instead, stick with your current amount and focus on becoming stronger and more active, so you can gradually increase your calories to a normal healthy level. If your calorie intake is already in a healthy range, decrease it only slightly, and only if necessary. A small reduction of about 250 calories a day, or 10-15 percent less than usual, is more likely to protect your lean muscle and less likely to trigger a slow-down in your metabolism.