TYPE 5 DIABETES IN LATIN AMERICA: AN INVISIBLE PHENOTYPE AT THE INTERSECTION OF CHILDHOOD UNDERNUTRITION, FOOD INSECURITY, AND DIAGNOSTIC ERROR

Type 5 diabetes is the name proposed in 2025 for a form of diabetes that affects lean young individuals with a history of undernutrition, previously described as malnutrition-related diabetes mellitus and removed from the World Health Organization classification in 1999. Its defining feature is a marked deficiency in insulin secretion with preserved insulin sensitivity, in the absence of islet autoimmunity and of the tendency to ketoacidosis typical of type 1 diabetes. In Latin America, the coexistence of persistent food insecurity, a legacy of childhood stunting, and a rapid nutrition transition creates conditions in which this phenotype may occur, although it remains practically absent from regional epidemiological records and clinical protocols. In the absence of specific criteria, affected individuals tend to be labeled as having type 1 or type 2 diabetes, which may lead to inappropriate treatment, hypoglycemia, and loss of the opportunity for nutritional intervention. This review aimed to analyze type 5 diabetes as an invisible phenotype in Latin America, considering its biological bases, the regional determinants related to childhood undernutrition and food insecurity, and the consequences of diagnostic error. This is a narrative literature review, guided by a structured question based on the PICo strategy and directed at studies on the classification, pathophysiology, and social determinants of diabetes associated with undernutrition. The evidence shows that early undernutrition reduces beta-cell function, that stunted children from Brazilian urban slums already present lower insulin production, and that self-reported childhood hunger is associated with a higher likelihood of diabetes in older Brazilian adults. Clamp studies in individuals with low body mass index and diabetes describe a metabolic profile distinct from type 1 and type 2 diabetes, although the samples are small and not representative of Latin American populations. The recognition of the entity still faces conceptual criticism, related to the use of low body mass index as a marker of undernutrition and to the limited mechanistic evidence. It is concluded that type 5 diabetes should be incorporated into the diagnostic reasoning of Latin American health services, with the systematic recording of nutritional history, regional studies of characterization, and policies that articulate food security and diabetes care.