Malnutrition — Causes, Types, Kwashiorkor, RUTF & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Malnutrition is a broad term encompassing both undernutrition — where inadequate intake of energy, protein, or micronutrients causes deficiency disease — and overnutrition — where excess intake contributes to obesity and metabolic disease. Protein-energy malnutrition (PEM) exists on a spectrum from mild to severe acute malnutrition (SAM); its two extremes are marasmus (severe energy deficiency causing wasting) and kwashiorkor (severe protein deficiency causing oedema). SAM is defined by a mid-upper arm circumference (MUAC) below 115 mm, weight-for-height Z-score below -3, or bilateral pitting oedema. Globally, 735 million people are chronically undernourished; 3.5 billion lack essential micronutrients (iron, iodine, zinc, vitamin A, vitamin D — a phenomenon termed 'hidden hunger'). Undernutrition underlies approximately 45% of all deaths in children under 5 globally. In high-income countries, hospital malnutrition is highly prevalent — studies find 30-50% of hospitalised patients are malnourished, increasing complications, length of stay, and mortality.

Primary malnutrition (inadequate dietary intake): food insecurity, poverty, conflict, drought, and displacement are the main drivers globally. Poor infant and young child feeding practices — suboptimal breastfeeding and delayed or inadequate complementary feeding — account for the majority of childhood malnutrition in low-income settings. Secondary malnutrition (from underlying disease): gastrointestinal malabsorption syndromes (coeliac disease, Crohn's disease, short bowel syndrome, chronic pancreatitis); chronic illness with increased metabolic demands and anorexia (cancer, chronic infection including tuberculosis and HIV, COPD, heart failure, CKD); eating disorders (anorexia nervosa, avoidant-restrictive food intake disorder); dysphagia from stroke or neurological disease; and prolonged hospitalisation. Micronutrient deficiency causes: iron deficiency (from poor dietary intake and gastrointestinal blood loss — most prevalent nutritional deficiency globally, affecting 1.6 billion people); iodine deficiency (insufficient dietary iodine from soil-depleted crops); vitamin A deficiency (poor intake of animal products and orange-coloured vegetables in low-income countries); vitamin D deficiency (limited sunlight exposure and low dietary intake — endemic in Northern Europe); vitamin B12 deficiency (vegan/vegetarian diets, pernicious anaemia, metformin therapy).

Severe acute malnutrition — marasmus: extreme muscle and subcutaneous fat wasting producing a 'skin and bones' appearance; weight less than 70% of expected for height; wizened, old-looking face; irritability and apathy; no oedema. Kwashiorkor: bilateral pitting oedema (from severe hypoproteinaemia — serum albumin below 25 g/L); relatively preserved weight despite severe protein depletion; distended abdomen (from ascites and hepatomegaly — fatty liver from absent apolipoprotein synthesis); skin changes (flaky paint dermatosis); reddish-brown discolouration and thinning of hair; apathy and misery. General undernutrition: fatigue, weakness, inability to concentrate, impaired immune function (increased infection frequency and severity), poor wound healing, muscle wasting, and growth failure in children. Micronutrient deficiency signs: night blindness and Bitot's spots (vitamin A deficiency); peripheral neuropathy and megaloblastic anaemia (vitamin B12 and folate deficiency); koilonychia, pica, and fatigue (iron deficiency); goitre (iodine deficiency); rickets or osteomalacia (vitamin D deficiency); scurvy — perifollicular haemorrhages and gum disease (vitamin C deficiency).

Nutritional screening: MUST (Malnutrition Universal Screening Tool) — validated 5-item tool used in hospital and community settings; scores body mass index, unintentional weight loss, and acute disease effect; scores 0 (low risk), 1 (medium risk), 2+ (high risk). Anthropometric assessment: BMI (under 18.5 kg/m2 suggests underweight; under 16: severe undernutrition); unintentional weight loss greater than 10% of body weight in 6 months; mid-upper arm circumference (MUAC) below 115 mm: severe acute malnutrition in children under 5; 115-125 mm: moderate acute malnutrition; weight-for-height or weight-for-age Z-scores (WHO growth standards). Biochemical tests: serum albumin (below 25 g/L: severe; but note this is a poor marker of acute nutritional status — it is an acute-phase reactant lowered by inflammation); serum prealbumin/transthyretin (shorter half-life than albumin — better reflects acute nutritional changes); haemoglobin and MCV (iron deficiency, B12/folate deficiency anaemia); ferritin, serum iron, TIBC; vitamin D (25-OH), B12, folate; serum zinc; thyroid function. Functional assessment: hand grip strength (dynamometry) — validated marker of muscle mass loss and clinical outcome predictor.

Severe acute malnutrition (SAM) in children — uncomplicated (no medical complications, appetite present): community-based management with Ready-to-Use Therapeutic Food (RUTF — peanut-based paste such as Plumpy'Nut at 200 kcal/kg/day); 8-12 week outpatient programme; WHO growth monitoring with structured follow-up. Complicated SAM (anorexia, oedema, medical complications): inpatient stabilisation with F-75 therapeutic milk (75 kcal/100 mL) in the stabilisation phase (prevent hypoglycaemia, treat infections); transition to F-100 (100 kcal/100 mL) in the rehabilitation phase; treat infection (amoxicillin), correct electrolytes (potassium, phosphate, magnesium), and avoid cardiac overload. Refeeding syndrome prevention: start nutritional support slowly (20-25 kcal/kg/day initially), replace phosphate (give prophylactic thiamine 200-300 mg IV before starting refeeding in severely malnourished patients — to prevent Wernicke's encephalopathy from thiamine deficiency uncovered by carbohydrate loading). Adult hospital malnutrition: oral nutritional supplements (ONS — high-energy/protein drinks such as Ensure, Fortisip); nasogastric or gastrostomy enteral feeding when oral route is inadequate; parenteral nutrition (PN) for patients with non-functional gut. Micronutrient supplementation: targeted to specific deficiency — iron and folic acid (anaemia); vitamin D; vitamin B12 (intramuscular hydroxocobalamin for deficiency due to malabsorption).

Refeeding syndrome: the most dangerous complication of initiating nutritional support in severely malnourished patients — rapid carbohydrate loading drives intracellular uptake of phosphate, potassium, and magnesium from already depleted extracellular stores, causing profound hypophosphataemia, leading to cardiac arrhythmias, cardiac failure, respiratory failure, seizures, and death. Risk is highest with BMI under 14 or 20% weight loss. Prevention requires slow nutritional escalation, prophylactic phosphate and thiamine supplementation, and electrolyte monitoring. Immune deficiency: protein-energy malnutrition profoundly impairs both innate and adaptive immunity — malnourished children are 5-10 times more susceptible to severe infectious disease (measles can be fatal in malnourished children). Growth failure in children: irreversible stunting (low height-for-age) from chronic undernutrition — associated with lifelong cognitive impairment, reduced educational attainment, and reduced adult productivity. Organ failure in end-stage SAM. Pellagra (niacin/tryptophan deficiency), Wernicke-Korsakoff syndrome (thiamine), scurvy (vitamin C) — each potentially fatal if untreated.

Infant and young child feeding: promote exclusive breastfeeding for the first 6 months; introduce nutritious, age-appropriate complementary foods from 6 months while maintaining breastfeeding to 2 years. Population-level interventions: food fortification programmes (iodised salt — virtually eliminates goitre; iron-fortified flour; vitamin A supplementation in high-prevalence countries). Nutritional surveillance: MUAC screening of children under 5 in high-risk communities allows early identification and treatment before SAM develops. Hospital malnutrition: routine nutritional screening of all admitted patients using MUST within 24 hours of admission; early dietitian review and nutritional intervention for all at-risk patients. Community education: diverse diets promoting consumption of fruits, vegetables, legumes, and animal products alongside staple foods. Address underlying poverty, food insecurity, and social determinants of health through social safety nets, school feeding programmes, and agricultural development.

Seek urgent medical attention for: a child with bilateral leg oedema (kwashiorkor) or severe wasting (MUAC under 115 mm) — this is a medical emergency requiring specialist nutritional rehabilitation; any patient developing hypophosphataemia, cardiac arrhythmia, or respiratory distress after starting oral supplements or tube feeding (refeeding syndrome requires immediate medical management). See a GP for: unintentional weight loss over 5% in 3 months or over 10% in 6 months; fatigue, muscle weakness, or inability to maintain normal activities despite adequate perceived caloric intake; symptoms of specific micronutrient deficiency (symptoms of B12 deficiency, night blindness, anaemia, peripheral neuropathy). Refer to a dietitian for: MUST score of 2 or above in hospital or community; persistent weight loss with a chronic disease; eating disorders; and planning nutritional support for cancer, COPD, or organ failure patients.