Malnutrition — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Malnutrition is a broad term encompassing all forms of poor nutritional status, including undernutrition (deficiency of energy, protein, or micronutrients), overnutrition (excess of energy or specific nutrients), and micronutrient imbalance. The Global Burden of Disease study identifies malnutrition as the leading cause of poor health globally when all forms are included. Undernutrition — the focus of this page — affects 735 million people chronically and is classified into: stunting (chronic undernutrition causing low height-for-age — affects 148 million children under 5); wasting or severe acute malnutrition (SAM — acute protein-energy deficiency causing low weight-for-height — affects 45 million children and is the most immediately life-threatening form); underweight (low weight-for-age); and micronutrient deficiencies (hidden hunger — iron, iodine, zinc, vitamin A, folate deficiencies affecting over 2 billion). SAM in children under 5 is directly or indirectly responsible for 45% of child deaths globally. In high-income countries, malnutrition is increasingly a problem of hospitalised patients, elderly individuals, and those with chronic diseases (disease-related malnutrition — DRM).

In low-income countries: food insecurity (poverty, conflict, drought, crop failure), restricted dietary diversity, poor infant and young child feeding practices (suboptimal breastfeeding, inadequate complementary feeding), recurrent infections (diarrhoea, pneumonia, malaria, intestinal worms — creating a vicious cycle with malnutrition as both cause and consequence), inadequate water, sanitation and hygiene (WASH), and poor maternal nutrition (foetal programming — maternal malnutrition causes low birth weight and intrauterine growth restriction). In high-income countries and hospitalised patients: malabsorption syndromes (Crohn's disease, coeliac disease, short bowel syndrome, chronic pancreatitis), cancer (cachexia — cytokine-mediated muscle wasting), chronic organ failure (heart failure — cardiac cachexia; COPD; CKD; liver cirrhosis), post-surgical recovery, dysphagia (stroke, dementia), medication side effects (reduced appetite), depression, eating disorders (anorexia nervosa), alcohol use disorder, and social isolation in elderly individuals. Protein-energy malnutrition types: kwashiorkor (protein deficiency with oedema — hypoalbuminaemia; characteristic distended abdomen, skin changes, hair changes); marasmus (severe calorie deficiency — generalised muscle and fat wasting without oedema).

In children: growth faltering — failure to gain weight or height according to WHO growth charts; MUAC (mid-upper arm circumference) below 11.5 cm indicates SAM in children aged 6–59 months (below 12.5 cm indicates moderate acute malnutrition). Marasmus: severe wasting of muscle and subcutaneous fat — loose skin, elderly appearance; irritability; apathy. Kwashiorkor: bilateral pitting oedema (feet to body); flaky paint skin rash; hair depigmentation (flag sign — alternating light and dark bands reflecting periods of adequate and inadequate nutrition), diffuse hair loss; distended abdomen; lethargic, miserable affect. Severe acute malnutrition (SAM): defined by MUAC below 11.5 cm or WHZ below -3 or bilateral pitting oedema — immediately life-threatening, high risk of sepsis, hypothermia, hypoglycaemia. In adults and hospitalised patients (GLIM criteria 2019): unintentional weight loss above 5% in 6 months or above 10% in 6 months to 2 years; reduced body mass index (below 18.5 in adults, age-specific thresholds in elderly); reduced muscle mass; reduced food intake or assimilation (above 50% below requirements for more than 1 week). Clinical signs: muscle wasting (temporal wasting, interosseous muscle wasting), subcutaneous fat loss, oedema in protein-energy malnutrition, hair thinning and nail changes (koilonychia in iron deficiency), cheilosis and angular stomatitis (B vitamins), glossitis.

Anthropometric assessment: in children — weight-for-height Z-score (WHZ), height-for-age Z-score (HAZ), weight-for-age Z-score (WAZ), and MUAC; WHO growth standards (2006) used as the reference. MUAC is the strongest predictor of mortality risk and easiest field measurement — MUAC tape widely used in community screening. In adults — BMI below 18.5 (underweight; below 17 moderate; below 16 severe), weight loss history, calf circumference, grip strength. Malnutrition screening tools: MUST (Malnutrition Universal Screening Tool — for hospital and community adults — BMI plus weight loss plus acute disease effect scores, 0–4 risk); NRS-2002 (Nutritional Risk Screening — hospitalised adults); MNA-SF (Mini Nutritional Assessment — elderly); PG-SGA (Patient-Generated Subjective Global Assessment — cancer patients). Biochemical markers: serum albumin (reflects disease severity more than nutritional status — acutely lowers in inflammation; below 30 g/L indicates poor prognosis); pre-albumin (shorter half-life — better short-term nutritional marker); serum zinc, iron, ferritin, folate, vitamin B12, vitamin D, magnesium, phosphate (critical to check pre-refeeding). Refeeding syndrome risk: check phosphate, potassium, magnesium before and during nutritional support in severely malnourished patients.

Severe acute malnutrition (SAM) without complications (no oedema, no anorexia, no infection — can be managed outpatient, over 75% of SAM cases): ready-to-use therapeutic food (RUTF — Plumpy'Nut — peanut-based paste enriched with micronutrients and high calorie density, 500 kcal per packet) — UNICEF-WHO protocol; community-based management of acute malnutrition (CMAM). SAM with complications (oedema — kwashiorkor, medical complications — inpatient management): WHO 10-step guideline: (1) treat hypoglycaemia, (2) treat hypothermia, (3) treat dehydration (oral rehydration solution — low sodium ReSoMal, not standard ORS), (4) correct electrolyte imbalance, (5) treat infection (empiric antibiotics — ampicillin plus gentamicin), (6) correct micronutrient deficiencies, (7) begin cautious feeding (F-75 therapeutic milk — 75 kcal/100 mL, 0.9 g protein), (8) achieve catch-up growth (F-100 — 100 kcal/100 mL), (9) sensory stimulation, (10) prepare for follow-up. Disease-related malnutrition in adults and elderly: oral nutritional supplements (ONS — high-calorie, high-protein drinks such as Fortisip, Ensure Plus — 1.5–2.5 kcal/mL, 7–20 g protein per 200 mL); nasogastric tube feeding if oral intake inadequate; percutaneous endoscopic gastrostomy (PEG) for long-term enteral feeding. Parenteral nutrition (intravenous nutrients via central line): for patients with non-functional gut (short bowel syndrome, ileus, bowel obstruction, GI fistula) — high risk of catheter-related infection. Refeeding syndrome: cautious refeeding in severely malnourished patients — start at 10 kcal/kg/day, monitor phosphate, potassium, magnesium (supplement proactively), and increase gradually (thiamine supplementation mandatory before feeding in suspected chronic alcohol use). Micronutrient supplementation: vitamin A (megadose prophylaxis in SAM — reduces child mortality), zinc (shortens diarrhoea duration), folate, iron (defer in SAM until infection resolved).

Malnutrition causes a cascade of serious organ-level and systemic complications. In children, severe acute malnutrition (SAM) carries an untreated case fatality rate of 20–30%. Growth faltering leads to irreversible stunting (height-for-age Z-score below -2 SD) affecting 148 million children globally — stunted children have impaired cognitive development, reduced IQ scores, lower school completion rates, and reduced adult earning capacity. Immune compromise — both cellular and humoral immunity are profoundly suppressed — dramatically increases susceptibility to pneumonia, diarrhoea, measles, and tuberculosis; infection and malnutrition form a vicious cycle where each worsens the other. Micronutrient deficiency complications include: vitamin A deficiency causing xerophthalmia, corneal ulceration, and preventable blindness (250,000–500,000 children annually); iron deficiency anaemia impairing cognitive development and work capacity; zinc deficiency impairing wound healing, immune function, and growth. Refeeding syndrome — severe hypophosphataemia, dangerous cardiac arrhythmias, and potential cardiac arrest from over-rapid nutritional repletion — is a potentially fatal complication of treating SAM; mandatory thiamine supplementation and slow calorie escalation are required to prevent it. In hospitalised adults, malnutrition increases postoperative complication rates 2–3 fold, prolongs hospital stays by an average of 3–5 days, and significantly raises mortality in critical illness. Oedematous malnutrition (kwashiorkor) causes hepatomegaly, ascites, and impaired hepatic synthesis of clotting factors and albumin. Severe sarcopaenia weakens the diaphragm and respiratory muscles, worsening pneumonia outcomes and prolonging mechanical ventilation requirements.

Global level: food security programmes, social protection (conditional cash transfers), community gardening and agriculture development; WASH (safe water, sanitation, hygiene to reduce infection-malnutrition cycle). Maternal and child nutrition: exclusive breastfeeding for the first 6 months of life reduces malnutrition and child mortality; continued breastfeeding with appropriate complementary foods from 6 months to 24 months. Therapeutic zinc, vitamin A, and iron supplementation in deficient populations. Nutritional surveillance using MUAC screening in community health programmes. Hospital and institutional settings: nutritional screening on hospital admission with MUST or NRS-2002 — NICE guidelines mandate this for all patients; dietitian referral for all malnourished patients; fortified meals and assistance with eating for elderly patients who cannot feed themselves; regular weighing during hospitalisation. Individual level: maintain adequate dietary diversity across all food groups; protein-rich foods for elderly (minimum 1–1.2 g/kg/day); prevent social isolation and depression in elderly (major causes of poor appetite and weight loss). Deworming programmes (albendazole, mebendazole) reduce intestinal worm burden that contributes to malnutrition in tropical settings.

Seek emergency care immediately for a child who is extremely lethargic or unconscious, has bilateral pitting oedema of both legs (kwashiorkor), has MUAC below 11.5 cm, has refused food and is severely wasted, or develops watery diarrhoea with dehydration — severe acute malnutrition in children is a medical emergency with high mortality. Adults should seek medical review for: unintentional weight loss of more than 5% of body weight within 3–6 months (especially if appetite is reduced — may indicate underlying cancer, chronic disease, or depression); inability to eat or swallow normally for more than 3 days; significant muscle weakness or loss of ability to perform daily activities. Elderly individuals living alone with unintentional weight loss should be assessed promptly — nutritional decline in the elderly is often missed until severely advanced. Report any child not gaining weight normally according to their growth chart to a healthcare professional.