When you restrict calories to a severe degree, or fail to eat on a regular schedule (you should eat six times per day) your body goes into starvation mode.  In starvation mode, fat is hoarded.  Fat is a storage fuel and its main purpose on your body is to keep you alive when food is in short supply.  Muscle on the other hand is a highly metabolic active tissue.  It requires a lot of fuel and energy to be maintained.  It is also extremely heavy.  Therefore, when the body is confronted with decreased food intake, it figures the most efficient fuel source to utilize is muscle.  For some women, you may think this is a good idea, but it is not.  One pound of muscle burns 35 calories per day at rest.  Simple math will tell you that the more muscle you have on your body , the more calories you burn every single day.  This is one of the reasons that men have an easier time losing weight than women.  Men simply have more muscle on their bodies than women.

This loss of muscle also happens to people who engage in long duration endurance activities.  These would include activities such as running and biking for long distances.  Once again, the body looks for efficiency.  It is not efficient to carry extra weight and, therefore, the body sacrifices muscle for energy.  Spending long hours, working out on cardiovascular equipment, is another strategy that leads to dieting failure.

Muscle is the secret key to long-term weight loss success.  The more muscle you have on your body, the more calories you burn.  This equates to being able to eat more calories and still maintain your weight.  For those concerned about looking overly muscular from adding muscle, fear not.  Most people can easily put on 10 pounds, or more, of muscle and the only change they will notice is that they look more "tone".  You will certainly not be overly muscular.

Simply stated, most diets fail because a large percentage of the weight loss during the diet is muscle mass.