The Fifth Type: Malnutrition-Related Diabetes Mellitus as an Emerging Public Health Crisis in the World’s Diabetes Capital

Dear Sir, India is referred to as the “Diabetes capital of the world” and faces a significant burden of diabetes mellitus, with an estimated 77 million cases in 2019, projected to rise to 134 million by 2045.[1] While both Type 1 and Type 2 diabetes are well characterized, a distinct form, malnutrition-related diabetes mellitus (MRDM), recently termed “Type 5 diabetes” by the International Diabetes Federation (IDF) in January 2025, has emerged as a critical concern, particularly in low- and middle-income countries like India.[2,3] This condition, linked to chronic undernutrition, affects lean, malnourished adolescents and young adults, posing unique challenges for diagnosis and management. This article reviews the epidemiology, clinical characteristics, public health implications, and research gaps surrounding Type 5 diabetes in India, emphasizing the need for targeted interventions and public health policy to address this underrecognized condition. EPIDEMIOLOGY AND RECOGNITION Type 5 diabetes or MRDM is estimated to affect 20–80 million people globally, predominantly in Asia and sub-Saharan Africa, with India being a significant hotspot due to its high prevalence of malnutrition.[2] Initially identified in the 1950s as “J-type diabetes” in Jamaica and later in India, it was classified by the World Health Organization (WHO) in 1985 as a distinct diabetes type but was removed in 1999 due to insufficient evidence.[3] A 2023 meta-analysis solidified the link between malnutrition and impaired pancreatic function, prompting the IDF to reclassify it as Type 5 diabetes in 2025, with formal endorsement at the 75th World Diabetes Congress in April 2025.[3] In India, the National Family Health Survey (NFHS-5, 2019–2021) reported a diabetes prevalence of 11.4%, with an estimated 31 million new cases, some of which may include Type 5 diabetes due to diagnostic overlap.[4] Approximately 40% of Indian children are born underweight, contributing to the risk of MRDM.[5] CLINICAL CHARACTERISTICS Type 5 diabetes is characterized by severe insulin deficiency due to impaired pancreatic beta-cell development caused by chronic nutrient deficiencies, particularly during childhood or adolescence.[2] Unlike Type 1 diabetes, which involves autoimmune beta cells destruction, or Type 2 diabetes, marked by insulin resistance, Type 5 diabetes results from malnutrition-induced pancreatic damage.[2] A study in 73 low-body mass index (BMI) Asian Indian men, demonstrated that individuals with Type 5 diabetes had lower insulin secretion, reduced visceral adipose tissue, and higher glucose uptake compared to those with Type 2 diabetes, confirming its unique metabolic profile.[3,6] Clinical features include excessive thirst, polyuria, fatigue, weight loss, stunted growth, frequent infections, poor wound healing, and a BMI typically below 19 kg/m².[3] Unlike Type 1 diabetes, patients do not develop ketonuria or ketosis despite high blood glucose levels, and insulin injections may lead to hypoglycemia, necessitating alternative treatments like oral hypoglycemic agents.[7] PUBLIC HEALTH IMPLICATIONS The recognition of Type 5 diabetes underscores India’s dual burden of malnutrition and noncommunicable diseases. Chronic undernutrition, driven by socioeconomic factors such as poverty and food insecurity, is a key risk factor, particularly in rural areas where 40% of children are underweight.[5] The economic burden of diabetes in India is substantial, with treatment costs consuming 5–25% of household income and complications increasing costs by over 10%.[4] Misdiagnosis of Type 5 diabetes as Type 1 or Type 2 has led to inappropriate treatments, such as high-dose insulin, resulting in adverse outcomes like hypoglycemia.[3] Public health strategies should prioritize early screening, improved nutrition through high-protein diets (e.g., legumes), and affordable medications like metformin or low-dose insulin.[2] Addressing maternal and child undernutrition is critical to reducing the incidence of Type 5 diabetes as intrauterine growth retardation (IUGR) is a significant risk factor.[5] RESEARCH GAPS AND CONTROVERSIES Despite its recognition, Type 5 diabetes remains controversial due to limited modern evidence and diagnostic clarity. Some experts argue that rebranding MRDM as Type 5 diabetes lacks sufficient biological and epidemiological support, given declining undernutrition rates in India and weak diagnostic criteria.[3] The IDF has established a working group, cochaired by Indian endocrinologist Dr. Nihal Thomas, to develop standardized diagnostic tools and treatment protocols over the next 2 years.[3] Further research is needed to clarify prevalence, refine diagnostic criteria, and evaluate treatment efficacy, particularly in resource-limited settings. CONCLUSION Type 5 diabetes, or MRDM, represents an emerging public health challenge in India, driven by chronic malnutrition and affecting millions of lean, undernourished individuals. Its recognition by the IDF in 2025 marks a pivotal step toward improved diagnosis and management, but controversies surrounding its classification highlight the need for further research.[2,3] Public health interventions should focus on improving nutrition, enhancing healthcare access, and developing cost-effective treatments to address this condition, reducing the dual burden of malnutrition and diabetes in India. Integrating Type 5 diabetes into national health policies and prioritizing maternal and child nutrition programs are essential steps toward mitigating its impact. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.