Overview of Type 5 Diabetes

Type 5 diabetes, officially recognized by the International Diabetes Federation (IDF) in April 2025, is a distinct form of diabetes mellitus previously known as malnutrition-related diabetes mellitus (MRDM). It arises from chronic undernutrition, particularly during early childhood and adolescence, leading to impaired pancreatic development and severe insulin deficiency. This condition primarily affects lean, malnourished young adults and teens in low- and middle-income countries (LMICs), such as South-East Asia and sub-Saharan Africa, with an estimated global prevalence of 20–25 million people. Unlike type 1 diabetes, it does not typically involve ketosis or autoantibodies, and patients often require high doses of insulin for management despite a structurally normal pancreas.

The classification of type 5 diabetes as a standalone category was unanimously endorsed by an international panel of experts in January 2025 in India and later formalized at the IDF World Diabetes Congress in Bangkok. This recognition addresses historical underdiagnosis, where cases were often misclassified as type 1 diabetes, and aims to improve targeted diagnostics, therapies, and research in resource-limited settings.

Classification and Subtypes

Type 5 diabetes is not further subdivided into multiple subtypes in current classifications; it is treated as a single, homogeneous entity distinct from other diabetes types. However, historical and regional variations in MRDM (its predecessor term) have described potential phenotypic overlaps or informal subtypes based on clinical presentation and geography. These are not officially recognized under the type 5 nomenclature but provide context for its evolution: Historical/Informal Subtype Description Key Characteristics Geographic Association Fibrocalculous Pancreatic Diabetes (FCPD) A subset linked to chronic pancreatitis from malnutrition, involving pancreatic fibrosis and calculi (stones). Severe insulin deficiency; abdominal pain; requires insulin; no ketosis. Predominant in southern India and parts of Africa. Protein-Deficient Diabetes Mellitus (PDM) Emphasizes protein malnutrition as the primary driver, without evident pancreatic damage. Milder insulin secretion defect; responsive to oral agents initially; lean BMI. Seen in tropical regions like Jamaica (historically termed “J-type”). Ketosis-Resistant Youth-Onset Diabetes Focuses on young-onset cases without ketoacidosis despite hyperglycemia. High insulin needs; no family history of diabetes; micronutrient deficiencies. Common in Asia and Africa; overlaps with SIDD (severe insulin-deficient diabetes).

These informal distinctions stem from earlier World Health Organization (WHO) classifications in 1985, which introduced MRDM as a category before retracting it in 1999 due to insufficient evidence. The 2025 reclassification consolidates these under type 5 diabetes without endorsing subtypes, emphasizing its core pathophysiology: prolonged undernutrition disrupting beta-cell function and insulin production. Ongoing IDF working groups are developing formal diagnostic criteria, which may refine this in the future.

Distinction from Other Diabetes Types

For context, type 5 diabetes fits into the broader WHO/IDF classification as follows:

• Type 1: Autoimmune beta-cell destruction; ketosis-prone.
• Type 2: Insulin resistance with relative deficiency; obesity-linked.
• Type 3c: Pancreatogenic (e.g., due to pancreatitis or cystic fibrosis).
• Gestational: Pregnancy-related hyperglycemia.
• Type 5: Malnutrition-induced insulin deficiency; ketosis-resistant.

This unified approach under type 5 highlights health disparities and calls for nutrition-focused interventions alongside insulin therapy.