Protein–energy malnutrition (PEM), sometimes called protein-energy undernutrition (PEU), is a form of malnutrition that is defined as a range of conditions arising from coincident lack of dietary protein and/or energy (calories) in varying proportions. The condition has mild, moderate, and severe degrees.

Types include:

• Kwashiorkor (protein malnutrition predominant)
• Marasmus (deficiency in calorie intake)
• Marasmic kwashiorkor (marked protein deficiency and marked calorie insufficiency signs present, sometimes referred to as the most severe form of malnutrition)

PEM is fairly common worldwide in both children and adults and accounts for about 250 000 deaths annually. In the industrialized world, PEM is predominantly seen in hospitals, is associated with disease, or is often found in the elderly.

Note that PEM may be secondary to other conditions such as chronic renal disease or cancer cachexia in which protein energy wasting (PEW) may occur.

Protein–energy malnutrition affects children the most because they have less protein intake. The few rare cases found in the developed world are almost entirely found in small children as a result of fad diets, or ignorance of the nutritional needs of children, particularly in cases of milk allergy.