There are a variety of reasons people eat too few calories, including eating disorders, excessive athletic training, crash dieting and even senior citizens with reduced appetites. In addition to malnutrition, severely restricting caloric intake can take a toll on your normal bodily functions and lead to health problems. To stay healthy and stave off disease, don't stay on a low-calorie diet more than a few days and consult your health care provider if you're not able to consume enough calories to fuel your body's energy requirements.
A calorie is a term for the energy content of food, with most people needing between 1,000 and 2,000 calories every day for breathing, heart function, kidney function, cell metabolism and muscle activity. The calories you consume fall into one of two groups, those you need to stay alive and those needed for physical activity. The first group makes up your basal metabolic rate, or BMR, and varies according to your gender, age, height and weight. To determine your BMR, multiply your ideal body weight by 10, meaning that a woman weighting 150 lbs. would need 1,500 calories per day. Add 200 to 400 calories per hour of exercise, depending upon intensity.
Eating too few calories over time can lead to rapid weight loss. Although this may sound ideal to those who are overweight, losing a large amount of weight in a short time can increase cholesterol levels in your gallbladder and decrease its ability to excrete bile. This can lead to the formation of gallstones, hardened deposits of digestive fluid in your gallbladder characterized by severe pain, yellowed skin and a high fever and chills.
Severe calorie restriction may cause an iron deficiency and low protein levels that affect your immune system's ability to fight off colds and the flu and more serious illnesses. A report published in 2000 in "Medicine and Science in Sports and Exercise" noted that many athletes consume 25 percent fewer calories than they should, which increases inflammation and decreases anti-inflammatory immune factors. Increasing caloric and dietary fat intake to match energy expenditure reverses the negative effects on immune function.
Menstruation and Pregnancy
When women eat too few calories, it often leads to irregular menstrual periods or even causes periods to stop altogether. When menses stop, your risk of bone loss climbs due to a lack of estrogen and poor nutrition including low levels of calcium, increasing the risk for osteoporosis and broken bones. Women who eat too few calories during pregnancy can increase the chances their babies will experience delayed growth and development, have damaged organs and be prone to obesity in later life.
Metabolism and Weight Loss
Although it may seem counterintuitive, eating too few calories can make your body think it's in starvation mode and actually lose metabolism-boosting muscle and hold onto fat intead, sabotaging your weight-loss efforts. It causes your metabolism slow down overall and can make it harder to lose weight in the future.
If your body goes into starvation mode from eating too few calories for too long a period of time, it can cause abnormally low blood pressure, heart rhythm problems, hair loss, brittle fingernails, trouble concentrating, loss of coordination, decreased muscular strength, anemia and joint swelling. Your thyroid may also be affected, and you may feel cold all the time, with lower energy levels and increased depression.