Malnutrition is a medical condition that results from eating too few or too many nutrients. It is best known as the lack of adequate food supplies seen in developing countries and is the biggest killer of children in the world. However, in the United States malnutrition is becoming more common in elderly people. Malnutrition can be defined as both undernutrition and overnutrition. Undernutrition occurs when the body is lacking certain nutrients due to poor diet or malabsorption. Overnutrition is where the body is ingesting too many nutrients or there is an imbalance in nutrient levels.

Malnutrition can be caused by many factors, including lack of food, chronic illness, loss of appetite, alcoholism and lack of nutritional education. Signs and symptoms can also vary depending on the type of deficiency or toxicity. However, most who are malnourished experience symptoms such as extensive weight loss or gain, lethargy, hair and skin problems and poor wound healing. More serious types of malnutrition, such as protein-energy malnutrition and starvation, can affect the body more severely and even lead to death.

Malnutrition can take months or years to develop, and diagnosis of the underlying causes for malnutrition can be complex. Patients may be required to complete a diet journal in addition to a medical history and physical examination. Other tests, such as a complete blood count or x-rays, may be conducted. In many cases, malnutrition can be treated by replacing or restricting nutrients through the diet. In some extreme cases, physicians may recommend parenteral nutrition through an intravenous (I.V.) drip and liquid diets fortified with nutrients. Most complications of malnutrition can be reversed following treatment.