Type 2 diabetes in people who do not appear overweight

Diabetes in people who do not appear overweight by comparison with the background population has remained an area of uncertainty for clinical management. The concept that type 2 diabetes is not caused by ‘obesity’ but occurs when an individual exceeds a personal fat threshold has been a major step forward. This facilitates appropriate management for such people and also contributing towards in de-stigmatising the condition. Useful clinical information from the ReTUNE study of weight loss in people with normal or near normal BMI is not yet widely known. However, these advances introduce the need for much greater attention to precise diagnosis of the type of diabetes in people who appear lean. Specific testing identifies a much higher percentage of both monogenic diabetes and slow onset type 1 diabetes than expected in heavier groups with type 2 diabetes. How to approach this new diagnostic challenge is important. People with normal BMI account for around 1 in 8 people newly diagnosed with true type 2 diabetes in people of white European ethnicity. But the proportion is considerably greater in people of South Asian and Far Eastern ethnicity. Recognition of the difference between ethnicities in the range of BMI which may be regarded as normal calls for a fundamental rethink of weight classification. Although the BMI profile of people of black ethnicity is similar to that of people of white European ethnicity there are rarer specific clinical syndromes that require to be recognised.