The more exercise you perform, the more calories you burn and, in theory, the more weight you shed. When you push exercise and diet to extremes, however, you can throw your body out of balance and slow your progress in weight loss. Exercise improves your health, but lower weight and fitness do not necessarily mesh. Some elite athletes weigh more than couch potatoes who are the same height and age. Consult your doctor before beginning any new exercise or diet program.
You maintain a healthy weight by keeping in caloric balance — the number of calories you ingest matching the number of calories you burn off every day. When you eat more calories than you need, you store the excess in the form of fat tissue and you gain weight. Conversely, you lose weight when you have a caloric deficit day after day. One pound of excess weight equals 3,500 calories, so when you eat 500 calories less per day than you burn off, you lose 1 lb. of weight per week. Physical activity increases the number of calories you burn per day and can help speed weight loss.
Exercise and Metabolism
You need a certain number of calories each day just to maintain your basic bodily functions such as respiration and digestion. Your resting metabolic rate quantifies that need; your age, gender and current weight help determine this number. Exercise takes energy in the form of calories, and you increase your daily metabolic requirements with physical activity. Weight-bearing exercise also helps you build lean muscle mass, and when combined with a reduced-calorie diet, replaces fat tissue, the Marquette General Health System explains on its website. Because lean muscle mass burns more calories than fat tissue, your metabolism increases and you burn more calories per day. In theory, exercise aids weight loss. Overdoing it, though, can cause the numbers on your scale to stay the same or even rise.
You need energy to fuel intense exercise; when you cut back drastically on your calorie intake, your body senses trouble. Lacking the carbohydrates your muscles need to continue functioning, your body metabolizes fat tissue. When your body cannot access fat tissue, it actually eats away your muscle tissue to meet the demands you put on it during exercise. Too much exercise combined with too little nutrition puts your body in starvation mode; it shuts down your metabolism to protect itself. You become fatigued and lose endurance. Rather than burning more calories, your body lowers its needs and stores more fat. You stop losing weight and you might cut back calories further in response to the weight-loss stall, continuing the vicious cycle.
When you eat a healthy diet to fuel intense and prolonged exercise, you build strength and endurance. You build lean muscle mass and burn fat. That increased strength and muscle mass does not necessarily lead to continued weight loss, though, because muscle tissue is denser than fat. Inch for inch, muscle weighs more, so even if you look sleeker and feel fitter, your weight can stay the same or even go up, the Centers for Disease Control and Prevention explain.