Malnutrition is a disparity between the amount of food and other nutrients that the body needs and the amount that it is receiving. This imbalance is most frequently associated with under nutrition, the primary focus of this article, but it may also be due to over nutrition.
Chronic over nutrition can lead to obesity and to the metabolic syndrome, a set of cardiovascular risk factors characterised by abdominal obesity, a decreased ability to process glucose (insulin resistance), dyslipidaemia, and hypertension. Those 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, 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.
Under nutrition occurs when one or more vital nutrients are not present 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 infancy, adolescence, and pregnancy additional nutrition is crucial for normal growth and development. A severe shortage of food will lead to a condition in children called marasmus that is characterised 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 characterised by oedema (fluid retention), an enlarged liver, apathy, and delayed development. Deficiencies of specific vitamins can affect bone and tissue formation. A lack of vitamin D, for instance, can affect bone formation – causing rickets in children and osteomalacia in adults, while a deficiency in folic acid during pregnancy can cause birth defects.
- 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 under functioning immune system and a poorer prognosis. They frequently take longer to recover from surgical procedures and spend longer in hospital. Malnutrition is common in patients admitted to hospital but it is easily overlooked by hospital staff. For this reason, many hospitals screen and monitor the nutritional status of their patients. This approach is recommended by the National Institute for Health and Care Excellence (NICE). 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 with malabsorption (the inability of the body to absorb one or more available nutrients). Malabsorption may occur with chronic diseases such as coeliac disease, cystic fibrosis, pancreatic insufficiency, and pernicious anaemia. An increased loss of nutrients occur in chronic kidney disease, diarrhoea, and haemorrhaging. Sometimes conditions and their treatments can both 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 occur in patients who chronically abuse drugs and/or alcohol.
- Elderly patients 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 patients also frequently eat less due to a decreased appetite, decreased sense of smell, and/or mechanical difficulties with chewing or swallowing. For these reasons, elderly patients are more at risk of malnutrition and the requirement for nutritional support.