Metabolism is affected by body composition - the amount of muscle versus fat. People who are more muscular have higher metabolisms than those with more fat weight. According to the American Council on Exercise, even while asleep our skeletal muscles are responsible for more than 25 percent of our calorie use. Since muscle is so active, muscle burns about four times the energy fat does when we're at rest. So building muscle is not just for those who want to bulk up.
Strength training helps replace fat with muscle, thus contributing to a more speedy metabolism.
Losing weight through dieting without exercising results in a loss of muscle as well as fat. Your body composition does not necessarily change, and in some cases the percentage of fat weight will increase in proportion to muscle weight. Ultimately this could slow your metabolism, making it even harder to keep weight off. In a Tufts study, Nelson followed women who participated in identical diet plans. Those who did resistance training lost 44 percent more fat that those who just dieted.