Consuming calories is essential for the human body to function. Consuming too many calories can cause health problems, as can eating too few calories. Eating disorders, extreme diets and some medical conditions may cause a person not to consume enough calories. Medical treatment is needed in cases where malnutrition is causing health problems.
When someone restricts their caloric intake for an extended period of time, malnutrition can occur. People who have an eating disorder, such as anorexia nervosa or bulimia nervosa, are at risk for becoming malnourished. People who severely restrict their calories have slower metabolisms because their body goes into starvation mode and slows the body's functions to conserve energy. Frances Sizer and Eli Whitney write in "Nutrition and Concepts and Controversies" that people who are malnourished, the heart beats irregular or too quickly, the heart muscles can become thin and weak and the chambers of the heart decrease in size. As a result of malnutrition, heart attacks can occur.
When a person does not eat enough calories, the digestive tract can slow down to conserve energy. The digestive tract is responsible for breaking down food and drinks to the simplest form so that the body can use the nutrients to function. When a person isn't consuming enough calories, the stomach empties slower and the lining of the intestinal tract can shrink. When a person does eat, the digestive tract has been damaged so severely that it cannot properly digest food. The pancreas produces digestive enzymes more slowly and the person may experience diarrhea. Diarrhea only makes the problem worse by dehydrating the person and depleting essential vitamins and nutrients.
People who are restricting calories can develop nutrient deficiencies. Several deficiencies -- including iron, folate and vitamin B-12 deficiencies -- cause anemia, a disease that affects red blood cells. These cells are responsible for carrying oxygen to the organs and tissues of the body. An anemia associated with nutritional deficiencies can cause fatigue, shortness of breath, pale skin, irregular or fast heartbeat, dizziness, cognitive problems, cold hands and feet and headache. At first people who are anemic may not have any signs or symptoms, but as the condition goes untreated, signs and symptoms worsen and become noticeable. Nutritional deficiencies can also cause a range of other symptoms, including skin lesions, a lack of energy and diminished cognitive functioning.
Unhealthy Weight Loss
If you're restricting calories with the goal of losing weight, consuming far too few calories might sabotage your weight loss before it starts. Not only is severely restricting calories not sustainable -- you're bound to fall off the wagon and return to your old eating habits -- but it also causes your body to destroy muscle tissue. You should not lose more than two pounds a week during safe weight loss, explains West Virginia University. If you lose more than that, you're consuming too few calories.