Undernutrition
Undernutrition is a deficiency of calories or of one or more essential nutrients.
Undernutrition is usually thought of as a deficiency primarily of calories (that is, overall food consumption) or protein. Deficiencies of vitamins and minerals are usually considered as separate disorders. However, when calories are deficient, vitamins and minerals are likely to be also.
In developed countries, undernutrition is usually far less common than overnutrition (in which too many calories or too much of any specific nutrient--protein, fat, vitamin, mineral, or other dietary supplement--is consumed). However, undernutrition does occur, especially in people who are very poor, most notably the homeless, and in those who have psychiatric disorders. Also, people who become very ill may be unable to eat enough food because appetite is lost or their body's need for nutrients is greatly increased.
Undernutrition also occurs in older people. About 1 of 7 older people who live in the community consume less than 1,000 calories a day--not enough for adequate nutrition. As many as half of older people in hospitals and long-term care institutions do not consume enough calories. A deficiency of calories is the leading cause of death in children who live in developing countries.
A severe deficiency of calories causes a disorder called marasmus. Marasmus is common in many developing countries. It tends to develop in infants and very young children, who typically become thin and dehydrated. Breastfeeding usually protects against marasmus. A severe deficiency primarily of proteins causes a disorder called kwashiorkor. Kwashiorkor is less common than marasmus. The term is derived from an African word meaning "first child-second child," because a first-born child often develops kwashiorkor when the second child is born and replaces the first-born child at the mother's breast. Because children tend to develop kwashiorkor after they are weaned, they are usually older than those who have marasmus. Kwashiorkor tends to be confined to certain areas of the world where staple foods and foods used to wean babies are deficient in protein even though they provide enough calories as carbohydrates. Examples of such foods are yams, cassava, rice, sweet potatoes, and green bananas. However, anyone can develop kwashiorkor if their diet consists mainly of carbohydrates. People with kwashiorkor retain fluid, making them appear puffy and swollen.
If both calories and proteins are deficient, the resulting disorder is called marasmic kwashiorkor.
Starvation is the most extreme form of undernutrition. It results from a partial or total lack of essential nutrients for a long time.
 See the table How Starvation Affects the Body.
Causes
Undernutrition may result from lack of access to food; disorders that interfere with the intake, metabolism or absorption of nutrients; or a greatly increased need for calories.
The use of certain drugs may contribute to undernutrition. Many drugs decrease appetite. Some drugs cause nausea, which decreases appetite. Others (such as thyroxine and theophylline) increase metabolism, and still others (such as cholestyramine) interfere with the absorption of nutrients in the intestine, causing malabsorption. Also, withdrawal from certain drugs (such as antianxiety drugs and antipsychotics) or from alcohol may lead to weight loss.
Many factors work together to cause undernutrition in older people. Older people tend to consume less food. Those who eat alone may be less inclined to prepare and eat meals. Physical impairments or reduced mobility may make shopping for or preparing food difficult. Older people seem to require less food to feel full, possibly because age-related chemical changes decrease their drive to eat and increase their sense of satiety. A diminished sense of smell and taste may decrease the pleasure of eating. Also, as people age, the ability to absorb some nutrients is reduced.
Many disorders that are more common among older people can contribute to undernutrition. A stroke or tremors may make chewing, swallowing, or preparing food difficult. If tremors are continuous, as they are in Parkinson's disease, they cause weight loss by increasing the rate at which the body uses calories (metabolic rate). Dental problems, such as ill-fitting dentures or gum disease, may make eating painful or difficult. Malabsorption disorders, cancer (which can reduce appetite and increase the body's need for calories), and depression (which can decrease appetite) are common among older people. People with dementia may forget to eat and so lose weight. When dementia is advanced, people cannot feed themselves and may resist attempts to feed them. Older people also take many drugs that can result in weight loss.
 See the sidebar Causes of Undernutrition.
Symptoms
The most obvious sign of a deficiency of calories is loss of body fat (adipose tissue). When not enough calories are consumed, the body breaks down its own tissues and uses them for calories--much like burning the furniture to keep a house warm. The loss of fat is often first noticeable in the face: The cheeks are hollow, and the eyes seem sunken.
If the deficiency of calories is severe, adults can lose up to half of their body weight, and children can lose even more. Bones protrude, and the skin becomes thin, dry, inelastic, pale, and cold. The hair becomes dry and sparse, falling out easily. When this wasting away is due to a disorder, it is called cachexia.
Other symptoms include fatigue, an inability to stay warm, diarrhea, loss of appetite, irritability, and apathy, sometimes leading to unresponsiveness (stupor). In children who are severely undernourished, behavioral development may be markedly slow, and mental retardation may occur. The number of some types of white blood cells decreases, resembling what happens in people who have AIDS. As a result, the immune system is weakened, increasing the risk of infections. If the deficiency of calories continues for a long time, heart and respiratory failure may develop. Total starvation (when no food is consumed) is fatal in 8 to 12 weeks.
Diagnosis and Treatment
Doctors can usually diagnose undernutrition based on the person's appearance. Blood tests may be performed to measure the level of albumin, which decreases when people do not consume enough protein. A physical examination, x-rays, and blood tests may be performed to determine the effects of undernutrition.
For most people, treatment involves gradually increasing the number of calories consumed. Eating several small, nutritious meals each day is the best way. For people who have been starving, foods are reintroduced carefully.
Feeding Methods: Sometimes nutrients cannot be given by mouth. In such cases, nutrients may be given through a tube inserted into the digestive tract or into a vein (intravenously).
Tube feeding may be used to feed people whose digestive tract is functioning normally but who cannot eat enough to meet their nutritional needs (such as people with severe burns) or who cannot swallow (such as some people who have had a stroke). For tube feeding, a thin plastic tube (a nasogastric tube) is passed through the nose and down the throat until it reaches the stomach or small intestine. If tube feeding is needed for a long time, the tube can be inserted directly into the stomach or small intestine through a small incision in the abdomen.
Food given through a tube (enteral nutrition) should contain all the nutrients a person needs. Special solutions are available, but solid foods may be processed and given through a nasogastric tube. Food solutions may be slowly and continuously given or given in a more concentrated amount every few hours.
Tube feeding causes many problems, and the problems may be life threatening. The most common problem among older people is the inhalation (aspiration) of food into the lungs, causing pneumonia. Aspiration of food can be lessened by elevating the head of the bed to reduce the risk of spitting food up (regurgitation) and by giving the solution slowly. Some people have diarrhea and abdominal discomfort. The risks of administering too much water and of nutritional imbalances can be reduced by calculating the amount of water required and measuring the levels of dissolved minerals (electrolytes) and urea in the blood.
Intravenous feeding is used when the digestive tract cannot adequately absorb nutrients (for example, in people with a malabsorption disorder) or must be temporarily kept free of food (for example, in people with ulcerative colitis or severe pancreatitis). Food given intravenously (parenteral nutrition) can supply part of a person's nutritional requirements (partial parenteral nutrition) or all of them (total parenteral nutrition). Because total parenteral nutrition requires a large intravenous tube (catheter), it is inserted into a large vein, such as the subclavian vein, located under the collarbone.
With intravenous feeding, infection is a constant risk because the catheter is usually left in place for a long time and the solutions that pass through it contain a lot of glucose--a sugar--which promotes the growth of bacteria. People receiving total parenteral nutrition are closely monitored for signs of infection as well as for changes in weight and urine output.
People who are very undernourished are sometimes given drugs such as recombinant growth hormone, medroxyprogesterone (a progestin used as a contraceptive), or dronabinol (used to treat nausea) to promote weight gain.
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