Undernutrition is a type of malnutrition characterized by a deficiency in calories or protein, according to Merck Manuals. Sufferers of undernutrition are often deficient in essential vitamins and minerals as well.
Undernutrition is a subcategory of malnutrition in which the sufferer does not take in enough food to support his body's nutritional requirements. A deficiency of calories or protein usually must be present for categorization as undernutrition, as specific vitamin and mineral deficiencies may occur even with proper calorie intake, notes Merck Manuals.
People suffering from undernutrition may be unable to maintain other bodily functions such as physical activity, growth and resistance to disease and infection. Women may experience difficulties with pregnancy and lactation, as detailed by UNICEF. People who are undernourished are likely to be underweight, deficient in essential vitamins and have stunted growth.
The largest causes for undernutrition are insufficient food intake or infectious diseases, as described by South Sudan Medical Journal. These conditions are caused by poverty, poor living conditions and inadequate access to health care or proper nutrition. Infectious diseases that affect the digestive tract may cause undernutrition as the patient is either unable to consume the required amount of food, or the body is unable to absorb the necessary nutrients. Undernutrition in turn makes the body more susceptible to disease.