By eating well and exercising regularly, you may naturally grow lean, firm muscle. You don't need to rush to the next GNC to load up on pills if you want to bulk up. If you want to gain 15-20 pounds of lean muscle without taking steroids or other supplements, you need to follow a few muscle-building guidelines. The first thing you need to know is that muscles are built by using them. As soon as you stop doing something that uses your muscles, they start to lose weight. So if you want to build muscle, you have to be willing to put in the time and effort required. Most people who want to build muscle focus their energy on adding weight to their arms and legs immediately. But these are just the smallest parts of your body. To truly build muscle you need to work out all of the major muscle groups in the body at least twice a week. This will help you increase your metabolism so that you burn more calories even when you're not making any changes to your routine. Muscle growth depends on two main factors: nutrition and exercise. You need protein to build new muscles, and you get it from food. The more protein you eat, the more muscle you'll grow. A study conducted by Dr. Doug McGuff, associate professor of medicine at the University of Texas Southwestern Medical Center, showed that healthy individuals who supplemented their diets with protein gained more muscle than those who did not supplement their diets.