Managing weight and muscle mass can be challenging because of the feedback mechanisms that operate in the body. When you lose or gain weight, your body tries to restore its balance by adjusting your appetite and energy expenditure. However, these adjustments can have unwanted effects on your body composition. For example, when you lose weight, you may lose more muscle than fat, which can lower your metabolism and increase your hunger. When you gain weight, you may gain more fat than muscle, which can impair your health and function.