A low-calorie diet is a low-energy diet. The goal of a low-calorie diet is to create an energy deficit by providing fewer calories than your body needs so that the body has to draw upon the energy stored in body fat.
One pound of body fat stores about 3,500 calories, so to lose one pound, you need to consume 3,500 fewer calories. Experts recommend that you eat 500 to 1,000 fewer calories each day depending on your current weight and how many pounds you want to lose. At this pace, you can lose one to two pounds of body fat per week (500 fewer calories per day x 7 days per week = 3,500 calories = 1 pound per week). Exercise, which burns calories, also helps achieve weight loss.
A low-calorie diet can be recognized by the types of foods recommended and the way they are prepared. Fresh fruits and vegetables; whole-grain cereals and breads; nonfat milk, yogurt, and other dairy products; and lean meats, poultry, fish, and beans make up the bulk of the menu. Fried foods, salty snacks, rich sauces, and sugary, fatty desserts are limited.
Foods are prepared using low-calorie cooking methods. For example, meats, poultry, and fish are roasted, baked, or broiled -- not fried. Vegetables are steamed, boiled, or microwaved without using butter. Oils are used sparingly, and margarine, when used, is the reduced-fat, trans-fat-free type. Very importantly, portion control is stressed.
Although the number of calories consumed has to be reduced before you can expect to lose weight, it is possible to lower your calories too much. A real irony of dieting is that you actually lose more weight if you eat some food rather than if you eat nothing at all. The reason is that when too few calories are eaten, the body protects itself from the energy shortage by using available energy more economically. The body does this by slowing its metabolic rate (the rate at which it uses energy). This shift in the rate of metabolism when food is scarce has its roots early in human development.
As hunter-gatherers, our ancestors could not always count on regular meals. They ate whenever they found food. As protection against the possible ill effects of an unreliable food supply, this metabolic adjustment conserved energy when food was not available.
As the body becomes more efficient at using the energy on hand, it actually needs less. A smaller energy deficit results, and less body fat is lost. To avoid this response, the number of calories you consume generally should not go below your resting metabolic rate (that is, the rate at which your body burns calories when at rest). Resting metabolic rate is about 1,000 to 1,200 calories a day for women and about 1,500 to 1,800 calories for men. Diets that recommend consuming fewer calories than that are best followed only under the supervision of your doctor.
Very-low-calorie diets can do more than simply frustrate efforts to lose weight. If followed for an extended period of time, such diets can also lead to nutritional deficiencies. Eventually, the body will begin to break down muscle protein to provide energy. This loss of muscle also slows the metabolic rate, making weight loss even more difficult. And while a vitamin-mineral supplement added to a very-low-calorie diet may protect against nutritional deficiencies, supplements cannot ward off the loss of muscle protein.
Low-calorie diets are usually low in fat, because fat is high in calories. The next page explains how to eat a healthy low-fat diet.