If left untreated, all children with protein energy malnutrition will progress to develop a failure to thrive, poorly developed immune system which causes overwhelming bacteremia and sepsis which is the cause of death in most malnourished individuals.

The symptoms of protein energy malnutrition usually develop between the first and fifth year of life, and start with symptoms such as lethargy, irritability, failure to thrive, decreased muscle mass, diarrhea, and recurrent infections due to decreased immunity. Without treatment patients with protein energy malnutrition which comprises of kwashiorkor and marasmus present with changes in their facial appearance with children with kwashiorkor having moon faces while those with marasmus develop monkey-like face due to loss of subcutaneous fat pad in the cheeks. There is generalized edema, hepatomegaly, changes in skin, hair color and texture, recurrent infections like diarrhea with kwashiorkor which will eventually lead to overwhelming shock and sepsis and death.^[1][2][3]

Complications that can develop as a result of protein energy malnutrition are:^{[4][5][6][7][8]}

• Congestive heart failure
• Fatty liver disease
• Renal insufficiency
• Bacteremia and sepsis
• Immune dysfunction
• Disorders of endocrine system
• Permanent mental and physical retardation
• Shock
• Coma

The presence of severe of hypoproteinemia, hypoalbuminemia, electrolyte imbalance or an underlying HIV infection is associated with poorer prognosis among patients with protein energy malnutrition.^[9]