Malnutrition basically means "bad nutrition" and is a condition in which there is a disparity between the amount of food and other nutrients that the body needs for proper growth and health and the amount that it receives or takes in (absorbs). This imbalance is most frequently associated with undernutrition, the primary focus of this article, but it may also be due to overnutrition.
Chronic overnutrition can lead to obesity and to metabolic syndrome, a set of risk factors characterized by abdominal obesity, a decreased ability to process glucose (insulin resistance), dyslipidemia, and high blood pressure (hypertension). People with metabolic syndrome have been shown to be at a greater risk of developing type 2 diabetes and cardiovascular disease. Another relatively uncommon form of overnutrition is vitamin or mineral toxicity. This is usually due to excessive supplementation, for instance, with high doses of fat-soluble vitamins such as vitamin A rather than the ingestion of food. Toxicity symptoms depend on the substance(s) ingested, the severity of the overdose, and whether it is acute or chronic.
Undernutrition occurs when one or more vital nutrients are not present or available in the quantity that is needed for the body to develop and function normally. This may be due to insufficient intake, increased loss, increased demand, or a condition or disease that decreases the body's ability to digest and absorb nutrients from available food. While the need for adequate nutrition is a constant, the demands of the body will vary, both on a daily and yearly basis.
- During pregnancy, adequate nutritional support is crucial for normal growth and development of the fetus. A deficiency in folic acid during pregnancy can cause birth defects and increase the risk of low birth weight and preterm delivery.
- Children can develop a condition called marasmus as a result of a severe shortage of food. Marasmus is characterized by a thin body and stunted growth. If enough calories are given but the food is lacking in protein, a child may develop kwashiorkor, a condition characterized by edema, an enlarged liver, apathy, and delayed development. Deficiencies of specific vitamins can also affect bone and tissue formation. A lack of vitamin D, for instance, can affect bone formation, causing rickets in children. Worldwide, about one-third of all childhood deaths are linked to malnutrition. Food shortages and intestinal parasites are leading causes of malnutrition in the developing world. In the U.S., most cases of malnutrition can be attributed to poor or imbalanced diets.
- Acute conditions such as surgery, severe burns, infections, and trauma can drastically increase short-term nutritional requirements. People who have been malnourished for some time may have weakened immune systems and a poorer prognosis. They frequently take longer to heal from surgical procedures and must spend more days in the hospital. For this reason, many doctors screen and then monitor the nutritional status of their hospitalized patients. Patients having surgery are frequently evaluated both prior to surgery and during their recovery process.
- Chronic diseases may be associated with nutrient loss, increased nutrient demand, and/or malabsorption. Malabsorption may occur with chronic diseases such as celiac disease, cystic fibrosis, pancreatic insufficiency, and pernicious anemia. An increased loss of nutrients may be seen with chronic kidney disease, diarrhea, and hemorrhaging. Sometimes, both the conditions and their treatment can cause malnutrition through decreased intake. Examples of this are the decreased appetite, difficulty swallowing, and nausea associated both with cancer (and chemotherapy) and with HIV/AIDS (and its drug therapies). Increased loss, malabsorption, and decreased intake may also be seen in people who chronically abuse drugs and/or alcohol.
- Elderly people require fewer calories but continue to require adequate nutritional support. They are often less able to absorb nutrients due in part to decreased stomach acid production and are more likely to have one or more chronic ailments that may affect their nutritional status. At the same time, they may have more difficulty preparing meals and may have less access to a variety of nutritious foods. Older people also frequently eat less due to a decreased appetite, decreased sense of smell, and/or mechanical difficulties with chewing or swallowing.