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