In fact both weight loss and weight gain are a balance. Basically, when you eat you take in energy: carbohydrates, whether simple or complex, are converted to glucose which is in turn converted into energy by means of the Krebs Cycle in the mitochondria, also known as the Citric Acid Cycle. That energy which is not used up by out metabolism or by exercise is then stored either as glycogen in the liver, as fat to be used as energy source later on when it is needed, or in building muscle; the outcome is that you gain weight.

Training strength exercises can be used to ensure that the weight you gain is in building muscle rather than in making you fatter. It is simple to understand if you think of it in terms of an energy balance, between the energy added to your body and that used.

Our metabolism uses up some energy: that is the energy needed for the normal life processes of breathing, blood circulation and digestion among many others. Some people have high metabolic rates, where they use more energy than average through these processes, and some have low metabolic rates. That is one reason why some seem to be able to eat anything and never put on a pound, while others blow up just at the sight of a rasher of fatty bacon.

Exercise uses up even more energy, even just walking or doing normal chores. The energy that isn't used will be converted to body tissue. The balance is a simple one: take in more energy than you use and you will gain weight. Use more energy than you take in and you will lose weight. There is no other possibility, so if you want to lose weight you move the energy in and out balance more to the out side, and if you want to gain weight, you move it more to the in side of the equation.

Building muscle can be achieved by training strength exercises, although these need not be extensive. It is a simple matter of carrying out sufficient strength exercises to use up the excess energy in your body. The energy will then be converted to muscle mass rather than fat mass. Whether you use that extra 10 pounds in building muscle or increasing your waistline depends on how you work specific muscles: work your shoulders and chest and you will add muscle bulk to your pecs and shoulders' work your arms with weights and you will add bulk to your biceps and triceps.

However, the amount of exercise needed to gain weight of the right type depends on the relative carbohydrate and protein content in your diet You need the carbohydrates to generate energy and the protein to build up the muscle when you use the energy through training strength exercises. Building Muscle is as much a mass balance as fat building is, and it all depends on the amount of strength exercises you carry out,. And what parts of your body you carry it out on.