Many people believe that growth hormone (GH) plays an appreciable role in building muscle, and that by manipulating GH levels, you can gain a muscle-building advantage. This is NOT true for two reasons:
The primary role of GH is to increase the growth of connective tissue (think tendons and bone) and to stimulate fat breakdown to provide energy to fuel tissue growth. It has much less of an impact on muscle growth.
GH only has an appreciable impact on muscle growth when it is injected in supraphysiological doses that are far greater than could ever be naturally achieved in the healthy human body.
Although fasting and certain supplements can cause a rise in GH levels, this is transient and will be well within the normal physiological ranges. For this reason, there will be little effect on muscle growth.
Also, in the case of fasting, it’s silly to think that not eating will put you in a better position to build muscle. When you eat protein and carbs, you’re in an anabolic state—meaning that you’re giving your body the tools it needs to create muscle tissue and prevent its breakdown. If you’re fasting, you’re in a catabolic state and may be at some risk of losing muscle.