This narrative review synthesises evidence on Type 5 Diabetes Mellitus (T5DM) — a malnutrition-related, non-autoimmune, insulin-deficient diabetes phenotype formally recognised by the IDF in April 2025 — covering its epidemiology, molecular pathophysiology (DOHaD framework, beta-cell developmental failure), clinical features, and nutritional/pharmacological management.
T5DM affects an estimated 20–25 million people worldwide (4–5% of global diabetes burden), predominantly lean young adults (BMI < 18.5 kg/m²) aged 15–30 in LMICs; key hallmarks are marked insulinopenia, ketosis resistance despite severe hyperglycemia, absent diabetes autoantibodies, and preserved peripheral insulin sensitivity — with fatal iatrogenic hypoglycemia as the primary mortality driver when misclassified as T1DM.
- No randomised controlled trials exist; management guidance relies on clinical consensus and observational data only. - Causality between malnutrition and diabetes remains unresolved (malnutrition may be cause or consequence of hyperglycemia). - Diagnostic criteria lack universal biomarkers; reliance on BMI < 18.5 kg/m² as a malnutrition proxy is contested as methodologically insufficient.
In young, lean patients from food-insecure backgrounds with insulin-deficient, autoantibody-negative, ketosis-resistant diabetes, suspect T5DM and avoid standard high-dose insulin to prevent fatal hypoglycemia. Prioritise nutritional rehabilitation (35–40 kcal/kg energy, 1.2–1.5 g/kg high-biological-value protein, zinc/magnesium/vitamins A and D repletion) and introduce calories gradually at 20–25 kcal/kg/day to prevent refeeding syndrome.
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