Gaining muscle will not make you lose weight. In fact, gaining significant muscle mass without losing fat will make you actually gain weight. (But if you’re not lifting weights for hours every week, chances are you won’t gain significant muscle mass.)
Yet muscle burns more calories at rest than fat does, at a ratio of 5-6 calories (per day per pound) to 2. While it’s not the end-all to improved body composition (we’re only talking 50 calories per day per 10 pounds of muscle), it’s a fantastic begin-all.
Gaining strength increases your ability to be more active. Moving more means feeling better about yourself. Feeling better about yourself means better choices in the kitchen. And better choices in the kitchen is really what transforms body composition from dangerously sedentary to vibrantly healthy.