Protein-Energy Malnutrition in Adults
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Direct answer
Protein-energy malnutrition in adults is depletion of muscle and fat from inadequate intake, malabsorption or raised metabolic demand, presenting as marasmus or kwashiorkor, though mixed forms are common. The most dangerous complication is refeeding syndrome, which follows rapid reintroduction of calories in patients with low phosphate, potassium or magnesium.
What you must remember
- Marasmus: severe energy deficiency with profound fat and muscle wasting and no oedema.
- Kwashiorkor: oedema, hepatomegaly with fatty liver, apathy, and skin and hair changes from protein deficiency.
- Assessment: GLIM criteria require one phenotypic feature, such as weight loss, low BMI or reduced muscle mass, and one aetiological feature, such as reduced intake or inflammation.
- Albumin is not a nutrition marker: serum albumin falls with inflammation and fluid shifts, so it cannot diagnose or track malnutrition.
- Refeeding risk: BMI below 16, little or no intake for more than 10 days, or low potassium, phosphate or magnesium before feeding each signal high risk.
- Refeeding prevention: thiamine before feeding, feeding started at about 10 kcal/kg a day in high-risk patients, and electrolytes checked daily for the first few days.
- Route of support: oral supplements first, enteral feeding if the gut works, and parenteral nutrition only when enteral routes fail.
- Micronutrients: check zinc, magnesium, vitamin D and folate, and replace them during refeeding.
Worked example: a woman after twelve days of minimal intake
A 52-year-old woman with a previous gastrectomy has weeks of vomiting and has eaten little for twelve days. Her weight has fallen 18 percent over four months, her BMI is 15, and she is apathetic with some ankle oedema.
- Confirm malnutrition: GLIM assessment finds weight loss and low BMI as phenotypic features, with reduced intake and surgical disease as aetiological features, so malnutrition is established. Low albumin here reflects inflammation and fluid shifts rather than nutrition.
- Grade refeeding risk: Refeeding risk is high on BMI and intake alone. Before any feed, potassium, phosphate and magnesium are measured and each low value is corrected first, because feeding drives these ions into cells.
- Give thiamine first: Thiamine is given before calories, and feeding starts at about 10 kcal/kg a day, rising over four to seven days toward target.
- Monitor the heart and fluids: An ECG checks for arrhythmia, and fluid balance is watched for heart failure. Electrolytes and glucose are checked daily for the first week, since phosphate typically falls soonest.
- Choose the route: The route is enteral through a feeding tube if the bowel works, and parenteral support is added only if it does not.
- Plan recovery: The pathway ends with dietitian follow-up and a plan for micronutrient replacement. A malnourished adult often needs months rather than days to rebuild.
Where the examiner tests the refeeding trap
Examiners return to a short list of refeeding and classification points.
- Trap: starting a high-calorie feed before correcting electrolytes Correct: correct the electrolytes and give thiamine before the calories arrive, since the shift of ions into cells can precipitate heart failure, respiratory failure and arrhythmias.
- Trap: labelling adult malnutrition as marasmus or kwashiorkor alone Correct: these are the paediatric picture, and adults usually present with mixed disease in which energy and protein deficits coexist, so the answer should name both.
- Trap: using serum albumin as a nutrition marker Correct: albumin is a classic distractor, because it falls with inflammation, infection and fluid shifts whatever the intake.
- Trap: assuming obesity excludes malnutrition Correct: obesity does not exclude malnutrition, since sarcopenic obesity can coexist with deficiency.
Frequently asked questions
Why is albumin not used to diagnose protein-energy malnutrition?
Serum albumin is not used to diagnose protein-energy malnutrition because it falls with inflammation, infection and fluid shifts, independent of nutritional intake. Nutritional status is assessed through weight history, BMI, muscle mass and intake, using GLIM criteria in adults.
What are the GLIM criteria for malnutrition?
GLIM criteria require at least one phenotypic feature, such as weight loss, low BMI or reduced muscle mass, together with one aetiological feature, such as reduced food intake or inflammation. Severity is then graded by the degree of these features.
Which electrolytes must be corrected before starting feeding in refeeding syndrome?
Potassium, phosphate and magnesium must be corrected before starting feeding in refeeding syndrome, together with thiamine. These electrolytes fall as carbohydrate and insulin drive them into cells, and cardiac arrhythmia or respiratory failure can follow.
What starting calorie intake is used in high-risk refeeding?
Feeding in high-risk refeeding starts at about 10 kcal/kg a day and is increased slowly over several days toward the target requirement. Slow initiation limits the shift of phosphate, potassium and magnesium into cells, which causes refeeding syndrome.
How does marasmus differ from kwashiorkor?
Marasmus is severe energy deficiency with profound wasting of fat and muscle and no oedema, while kwashiorkor is protein deficiency with oedema, hepatomegaly and skin changes. Adult patients often have a mixed picture that combines features of both.