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Protein deficiency leads to a condition known as protein-energy malnutrition (PEM). This condition is rare in developed nations, occurring most frequently in areas of the world where food is scarce and hunger and starvation are common, such as developing countries. PEM causes severe weight loss, wasting and, in children, poor growth. Children with PEM may be particularly thin for their height or short for their age. There are two forms of PEM:

• Kwashiorkor. Kwashiorkor is a protein deficiency where there may still be adequate caloric intake. It generally occurs following a recent and sudden period of starvation. The body may still have enough fat to supply it with energy, but there is no intake of protein to resupply it with amino acids. The body does not store extra protein as it does with fat, so the levels of proteins and substances made from proteins (e.g., enzymes, hormones) in the body are greatly reduced. Protein carriers are also in short supply, so fat cannot be properly transported out of the liver. The liver becomes large and fatty, causing a noticeable bulge in the abdomen.
  
  Insufficient amounts of the protein albumin (responsible for maintaining fluid balance) are responsible for some of the distinguishing features of kwashiorkor. When albumin levels are not sufficient, fluids pool in various areas of the body, causing the swollen face and limbs that are characteristic of kwashiorkor.
  
  
• Marasmus. Marasmus includes a deficiency in both caloric intake and protein, characterized by muscle wasting following a prolonged period of starvation. The body is breaking down its own muscle tissue for energy. Eventually, even the muscles of the heart may be sacrificed. People with marasmus are often very still and quiet, using no more energy than absolutely necessary. Children with the condition generally do not even cry out for food.

Signs of less severe protein deficiency include anemia and hair loss. This condition is also rare in the United States because the typical American diet provides more protein than is needed. However, protein deficiency can occur, especially among the very poor and people with eating disorders (e.g., anorexia nervosa, bulimia nervosa).