You are in Women, Men, Aging . It also forces your body to break down muscle tissue to fuel its vital operations. But that muscle is the key to your metabolism, or the speed at which you burn calories.
More muscle means a faster metabolism and less body fat.
You do need to cut calories to lose weight. But you need to make sure you're eating at least 1,600 to 1,800 calories each day to keep your metabolism from shutting down. And never cut protein during a diet. If you're lifting weights, aim for twice that much. Pick a number in between.