• Clinical science

Protein-energy malnutrition (Protein-energy undernutrition)


Malnutrition is a significant cause of morbidity and mortality worldwide, leading to ∼ 45% of all deaths in children under the age of five. Approximately 52 million children have wasting with one-third (17 million) suffering from severe acute malnutrition. Even more children (∼ 154.8 million) have stunted growth, indicating widespread chronic malnutrition. In severe cases, primary protein-energy malnutrition (PEM) can develop, which has two major clinical forms: kwashiorkor and marasmus. Kwashiorkor is characterized by muscle atrophy, pitting edema, and distended abdomen with an enlarged fatty liver. It is caused by a deficiency of dietary protein despite sufficient calorie intake (e.g., from carbohydrates). Marasmus is the diffuse loss of muscle and fat tissue (without edema or distended abdomen) due to a severe state of total calorie deficiency of all macronutrients. Secondary PEM occurs due to illnesses affecting appetite, digestion, absorption, metabolism, and/or increased energy/protein demand. In addition to muscle atrophy, it is possible for patients to have clinical features of either marasmus or kwashiorkor. All PEMs are primarily clinical diagnoses; for primary PEM, WHO diagnostic criteria involve a child's weight-for-length/height and mid-upper arm circumference (MUAC). Thorough laboratory testing should also be conducted to evaluate for severity and complications. Treatment involves managing complications, rehydration, and careful nutritional rehabilitation to avoid refeeding syndrome. In the case of secondary PEM, underlying conditions should also be treated.


  • Protein-energy malnutrition (PEM) is a term that describes pathological conditions resulting from a deficiency of dietary protein and/or total calories.
  • Primary PEM: due to inadequate macronutrient intake
  • Secondary PEM: due to chronic illnesses or drugs disrupting appetite, digestion, absorption, metabolism, and/or increased energy/protein demand

Primary protein-energy malnutrition

Main types of PEM
Marasmus Kwashiorkor
  • All major nutrients
  • Primarily protein, e.g.:
    • Premature ceasing of breastfeeding
    • Chronic GI infectious diseases
    • Inadequate preparation of food with use of staple foods without necessary amounts of proteins (e.g., sweet potatoes, cassavas)
Calorie intake
  • Deficient
  • Can be normal or even high
  • Severe energy deficiency leads to a catabolic state → breakdown of adipose tissue, muscle, and eventually organ tissue for energy
  • Widespread in children living in resource-limited countries in Sub-Saharan Africa, South-East Asia, and Central America.
  • Marasmus is most common
Key clinical features

Marasmic kwashiorkor

Protein-deficient KWick MEALS lead to Kwashiorkor → Malnutrition, Edema, Anemia, fatty Liver, Skin lesions!

Marasmus causes Muscle wasting but no edema!


Secondary protein-energy malnutrition



PEM is primarily a clinical diagnosis. Laboratory testing should be conducted to assess the severity and complications. Additional testing may be required to determine the underlying condition for secondary PEM.

Clinical diagnosis [6]

Primary PEM

  • H&P: Take a thorough history and physical exam, focusing on nutrition/potential child maltreatment and typical clinical features.
  • Anthropometrics: Assess the degree of malnutrition.
    • Height/length
    • Weight
    • Weight-for-length/height(WFL/H) represented as a Z score or a percentile
    • Mid-upper arm circumference (MUAC)
    • BMI
  • WHO diagnostic criteria: for primary PEM in children aged 6–60 months [7]

Secondary PEM

Laboratory tests


  • Hydration (typically oral)
  • Nutritional rehabilitation: Must occur slowly to prevent refeeding syndrome
    • Should be initiated slowly at ∼ 20% above the child's recent intake.
    • Slowly increase calorie intake while monitoring lab values daily.
    • For kwashiorkor, protein should also slowly be introduced into the diet to avoid acute liver injury.
  • Treat complications (e.g., infection)
  • For secondary PEM

Refeeding syndrome is a frequent complication if nutritional rehabilitation occurs too rapidly (sudden shift from a catabolic to an anabolic state): It is characterized by fluid retention, hypophosphatemia, hypomagnesemia, and hypokalemia.


We list the most important complications. The selection is not exhaustive.