The Effects of Consuming Fewer Than 1000 Calories Daily

Healthy calorie intake depends on individual size and metabolism, but most adults need about 2,000 calories a day to function properly. According to the American College of Sports Medicine, women should never eat fewer than 1,200 calories per day, and men need at least 1,800. Liquid diets, starvation diets and fad diets that cut back to 1,000 or fewer daily calories may work temporarily, but the results won't last.

Loss of Muscle Tissue

• When your body doesn't get the energy it needs from calorie intake, it will go into a semi-starvation state and look for alternative energy stores in the body. Though the body will burn fat this way, over time it will also burn muscle tissue. This can eventually lead to heart problems and abnormal rhythms, since the heart is made of cardiac muscle.

Slower Metabolism

• The loss of muscle mass associated with restricted diets slows down the body's metabolism, since muscle is the main contributor to metabolic rate. This decreases the body's energy needs, so when a person starts eating normally again they will gain more weight than they would have gained before starting the diet. According the McKinley Health Center at the University of Illinois, a restricted-calorie diet can slow the metabolism up to 30%.

Fatigue

• A proper weight-loss plan should include an exercise regimen. Energy from calorie intake is needed to fuel these exercises, as well as everyday activities such as talking on the phone, typing on the computer, brushing your teeth and even digesting food. When you don't get enough calories to fuel these activities, you won't have the energy to exercise and even everyday activities will become exhausting and difficult.

Hunger

• Severely restricting calories -- either by skipping meals or eating tiny portion sizes -- will obviously lead to hunger. Eventually, it becomes impossible to ignore these hunger pangs, which can lead to eating excessively or binging. Once a crash dieter starts eating normally (or excessively) again, all the weight will come back. Cutting back calories can result in healthy, long-term weight loss, but cutting back to 1,000 or less calories will only work in the short-term.