Tony, To gain muscle mass = adequate protein intake PLUS exercise, preferablly resistance exercise. To increase muscle mass, you either have to fill (hydrate) muscle tissue fully with glycogen or actually INCREASE the myofibrils within the muscle tissue. The only way for an adult to add more myofibrils is to cause a SRESS to the muscles via resistance training. The body will ADAPT to this stress by adding more myofibrils (contractile units w/in the muscle) as long as the stress is sufficient and overtraining is avoided. Dieting alone will not increase muscle mass. The process of adding more muscle mass usually takes 3-6 months. Strength gains in the first couple of months of training are the result of neurological adaptations not actual changes in the muscle size. A person who reduces % of body fat without resistance training may appear more muscular, but in actuality did not gain muscle mass. In fact, most weight lose is a combination of fat and muscle, particularlly if protein intake is not adequate, i.e. low calorie dieting. The moral of the story: Eat adequate protein (0.7-1.0 g/day) and start resistance training. Your efforts will be well worth it. By adding more muscle mass, you will increase your metabolic rate. Also, one of the first signs of aging is a decrease in lean muscle mass. You can maintain a younger "biological" age by keeping your LBM as high as possible. Hope this helps. Ed Campbell, DC,CSCS