Protein Deficiency: Signs, Causes and Who Is at Risk

When to get medical help first

Severe protein malnutrition (kwashiorkor) can be life threatening if treatment is not given or comes too late. [1] Swelling (edema), a swollen belly, failure of a child to gain weight and grow, marked fatigue or apathy, and repeated infections are listed as symptoms. [1] Contact a child's health care provider if a child has these symptoms, and people in shock need emergency treatment right away; in the US, call 911. [1] In the UK, the NHS advises seeing a GP after unintentional loss of a lot of weight over 3 to 6 months or if you are worried that a child or older person is malnourished. [2] Do not try to diagnose or treat suspected deficiency yourself with protein powders or amino acid products.

What protein deficiency is

MedlinePlus describes kwashiorkor as a form of malnutrition that occurs when there is not enough protein in the diet. [1] More broadly, clinicians use the term protein-energy malnutrition, where protein and calories are both short. A diet that is merely lower in protein than a reference value is not the same as a deficiency disease. Official reference intakes (see Protein Intake Levels by Age, Sex and Country) are for groups of healthy people and are not cut-offs for diagnosis.

Who is at risk

The pages read do not name vegetarian or vegan eating as a cause. A 2019 review concluded that protein-rich plant foods such as legumes, nuts and seeds are sufficient for protein adequacy in adults on vegetarian or vegan diets, while noting the picture is more complex in older adults. [4] See Protein for Older Adults and Vegetarian or Vegan Diets.

Signs: what they can and cannot tell you

For kwashiorkor, MedlinePlus lists skin pigment changes, decreased muscle mass, diarrhea, failure to gain weight and grow, fatigue, hair changes, repeated infections, irritability, swelling and a rash. [1] For malnutrition in general, the NHS lists unintentional weight loss over 3 to 6 months, low body weight (BMI under 18.5), lack of interest in eating, tiredness, weakness, getting ill often and, in children, not growing at the expected rate. [2] These signs are not specific to protein. Hair, skin or nail changes, tiredness or muscle loss can have many causes, so symptoms alone cannot show a protein deficiency. A clinician takes a history, measures weight and height, and may order tests; MedlinePlus lists tests such as total blood protein, blood counts and kidney tests for kwashiorkor. [1] Laboratory ranges differ by lab and country, and a clinician interprets results alongside illness and medicines. At-home or hair-based "nutrient panels" are not diagnostic.

Treatment is clinician-led

For kwashiorkor, MedlinePlus says early treatment can lead to full recovery, calories are given first and proteins are started after other calories have provided energy, and food must be restarted slowly because suddenly eating high-calorie foods can cause problems. [1] For malnutrition in adults the NHS first suggests fortified foods high in calories and protein, snacks between meals and calorie-rich drinks, and then a doctor, nurse or dietitian may suggest nutritional drinks, supplements or a feeding tube. [2] A 2025 meta-analysis of dietitian-led medical nutrition therapy in adults with protein-energy malnutrition found low-certainty evidence of shorter hospital stays and better weight and quality of life in inpatients, and uncertain evidence for most outcomes in outpatients. [5] See Protein After Illness, Surgery and for Pressure Injuries.

Too little protein by choice or restriction

Some people are told to limit protein, for example with chronic kidney disease. The NIDDK says too little protein may lead to malnutrition, so the balance should be worked out with a dietitian or health care professional. [6] People who are pregnant or breastfeeding have higher reference values per kilogram, according to Health Canada's table. [7] Do not change a prescribed diet or medicine on your own. Ask a clinician or dietitian, including before using protein products if you have kidney or liver disease, take medicines or are having surgery.

What this page does not cover

Not covered: specific amounts to eat, supplements to treat deficiency, or tests to buy. Proper evidence not found, in the sources searched (MedlinePlus, NHS, NIDDK and PubMed searches on protein-energy malnutrition), for treating a suspected deficiency with over-the-counter protein or amino acid products outside clinical care. See Protein: What It Does and Are Protein Supplements Necessary?.