Yes, individuals who are thin or have a normal body mass index (BMI) can absolutely develop diabetes. This reality challenges the common belief that only people who are overweight or obese are at risk for the condition. Diabetes is fundamentally a disorder characterized by sustained high blood sugar levels, which occurs when the body either does not produce enough of the hormone insulin or cannot use the insulin it makes effectively. Body weight is only one of many factors influencing this complex metabolic process, which also includes genetics, fat distribution, and lifestyle. Approximately 10% of people diagnosed with Type 2 diabetes are considered to be of normal weight.
Why Appearance Does Not Equal Metabolic Health
External appearance, often measured by BMI, can be misleading when assessing a person’s internal metabolic status. A person who appears outwardly lean can still have an unhealthy metabolic profile, a condition sometimes referred to as “metabolically obese normal weight.” Insulin resistance, the primary defect in Type 2 diabetes where cells fail to respond properly to insulin, can occur regardless of a person’s subcutaneous fat levels.
This metabolic disconnect means that a person with a normal BMI might exhibit signs of poor health, such as high blood pressure, high triglycerides, or high blood sugar. Genetic factors and an inactive lifestyle can contribute to this internal vulnerability, predisposing some lean individuals to the same chronic diseases typically associated with higher body weight. The body mass index does not differentiate between muscle mass and fat mass, nor does it reveal where the fat is stored, making it an incomplete measure of health.
The Crucial Role of Internal Fat Distribution
The location where the body stores fat is often a greater predictor of diabetes risk than total body weight. Fat is stored in two main ways: subcutaneously, which is the pinchable fat under the skin, and viscously, which is the deep fat packed around internal organs like the liver and pancreas. Visceral fat is metabolically active and releases inflammatory molecules called adipokines and free fatty acids directly into the portal circulation.
This influx of inflammatory substances interferes with the liver’s function and directly promotes insulin resistance in both the liver and muscle cells. A lean person with a disproportionately high amount of visceral fat—the “thin outside, fat inside” phenomenon—has a risk profile similar to that of an obese person. Some individuals, particularly those of South Asian descent, are genetically predisposed to this pattern of internal fat accumulation, which explains why they may develop Type 2 diabetes at a lower BMI threshold.
Genetic Predisposition and Specific Diabetes Types
Beyond Type 2 diabetes driven by visceral fat, other forms of diabetes are largely independent of body weight, making lean individuals just as susceptible. Type 1 diabetes is an autoimmune condition where the body’s immune system mistakenly attacks and destroys the insulin-producing beta cells in the pancreas. This process leads to an absolute deficiency of insulin, and because it is an autoimmune attack, it is not caused by or related to body mass or lifestyle factors.
Latent Autoimmune Diabetes in Adults (LADA) is a slow-onset form of Type 1 diabetes that is often misdiagnosed as Type 2 because it appears in adulthood. People with LADA are often of normal weight and may not require insulin immediately, but they test positive for autoimmune antibodies typically found in Type 1 diabetes. This condition follows the same autoimmune mechanism as Type 1, but progresses slower, making leanness a common characteristic at diagnosis.
Maturity-Onset Diabetes of the Young (MODY) is a much rarer form of diabetes caused by a mutation in a single gene. This genetic condition typically runs strongly in families and causes diabetes before the age of 25, regardless of a person’s weight, diet, or activity level. MODY is a distinct, inherited disorder affecting insulin production or function, which often impacts lean individuals.
When Should Lean Individuals Be Screened
Screening recommendations for diabetes are evolving to recognize that weight alone is an inadequate measure of risk. The United States Preventive Services Task Force (USPSTF) recommends screening for prediabetes and Type 2 diabetes in all adults aged 35 to 70 who have overweight or obesity. However, the recommendation advises considering screening at a lower BMI for individuals from populations with a disproportionately high prevalence of diabetes, such as Asian Americans, for whom screening is suggested starting at a BMI of 23.
Lean individuals should be proactive about screening if they have other significant non-weight risk factors. A strong family history of Type 2 diabetes in a parent or sibling is a major indicator that warrants testing. Other factors that should prompt a discussion with a healthcare provider include:
- High blood pressure
- High cholesterol or triglycerides
- A history of gestational diabetes
- Symptoms like unexplained thirst or frequent urination
- Unexplained weight loss
Screening involves simple blood tests such as fasting plasma glucose or an HbA1c level.