Can Eating Too Few Calories Prevent Weight Loss?

How many calories you eat affects your energy levels, metabolic rate and overall health. Reducing calories below your body's maintenance level can promote weight loss, but eating too few calories can actually slow and even prevent weight loss. When you don't eat enough to fuel your body's basic processes and your activity level, your metabolic rate may slow to conserve energy. This means you burn fewer calories, and it becomes more difficult to lose weight.

Weight Loss

Age, gender, physical activity and your body composition affect weight loss. Because muscle loss and reduced physical activity cause a slower metabolic rate, older people often have more difficulty losing weight than younger ones. Women tend to have more difficulty losing weight than men, and sedentary people have a harder time losing weight than active people. Eating too few calories to support good health undermines your efforts. On an extreme diet of less than 1,100 calories, up to 30 percent of the weight loss may be from muscle loss, according to the University of Maryland Medical Center. In addition, eating too few calories in an attempt to lose weight can lead to weight gain when you return to normal eating.

Body Composition

Body composition refers to the ratio of muscle to fat. When you lose muscle due to age or inactivity, your metabolism slows down, meaning you burn fewer calories. Losing weight requires a 3,500-calorie deficit to lose 1 lb. If you eat too few calories, your body breaks down lean tissue for energy and holds onto fat. Because of this, you might lose weight eating too few calories, but much of that weight is from water and healthy tissue.

Metabolism

Low calorie diets without exercise resulted in slower metabolic rates and reduced physical activity in study participants, according to researchers from the Pennington Biomedical Research Center in Louisiana who reported their findings in the 2001 PLoS One, the Public Library of Science's Hub for Clinical Trials. Participants consuming either a diet with 25 percent calorie reduction or an 890-calorie diet performed less habitual and voluntary physical activity during the trial than a control group and a group undergoing 12.5 percent calorie reduction and 12.5 percent calorie expenditure in exercise. The researchers concluded diet and physical activity combined offer a potentially successful method for maintaining weight loss.

Calorie Intake

Sedentary women need an estimated 1,600 calories a day; active women and sedentary men need 2,000, and active men need 2,400, the Merck Manual advises. In addition to slowing your metabolism, eating too few calories puts you at risk for inadequate nutrition. Severe calorie restriction can cause fatigue, intolerance to cold, gallstones and menstrual irregularities. Consuming fewer than 800 calories a day can result in heart rhythm abnormalities and could even be fatal. Work with your physician or a nutritionist to devise an eating plan that is best for you.