Q: Is it possible to lose muscle mass with an exercise/weight loss program?
A: It is possible to lose muscle mass with an exercise/weight loss program. The key to losing weight is to burn more calories than you are consuming (creating a caloric deficit).
The traditional “diet” is the method most often used to create the caloric deficit by consuming fewer calories than you burn. A diet does lead to weight loss, but when you consume fewer calories than you burn, your metabolic rate slows down to meet the new intake level. If your caloric intake gets too low, your body actually starts burning muscle to sustain itself. Typically, diets result in weight loss, but with a corresponding loss in muscle mass and an increase in the fat to muscle ratio.
An exercise routine that includes strength training is a better way to manage weight loss. Exercising creates a caloric deficit by burning more calories than you are consuming. The strength training portion of the routine leads to an increase in muscle mass. In addition, an increased amount of muscle mass will increase your metabolic rate. The net result is weight loss, with an increase in lean muscle mass and a decrease in the fat to muscle ratio.
However, an exercise routine with poor nutrition, not enough calories, and lack of rest/recovery could lead to a loss in muscle mass by creating such a large caloric deficit that your body again burns muscle to sustain itself.