Why do South Asians get type 2 diabetes at much lower body weights? The answer is in their fat cells. These are fat cells from two young men with the same BMI. The South Asian man's are on the left. The white man's are on the right. At the same BMI as white Europeans, South Asians carry more body fat, bigger fat cells, more liver fat, and higher insulin. Here is what the studies show. 1. Same BMI, much bigger fat cells. In 29 South Asian and 18 white men, average age 27, BMI was 24 vs 23. Body fat was 22% vs 15%. The average belly fat cell was 3,491 vs 1,648 µm² in cross section. Treating the cells as spheres, that is about 3 times the volume of fat per cell on average. The samples in the image show an even larger difference. The larger the fat cells, the worse the insulin resistance. Visceral fat was the same in both groups. 2. Matched for age and BMI, still more insulin. Asian Indians matched to white adults had similar fasting glucose but higher fasting insulin, and they cleared glucose about 40% less well on a clamp test (4.7 vs 7.5 mg/kg/min). 3. Fat cell size explains much of the insulin gap. After adjusting for age, sex and BMI, South Asians had larger fat cells, liver fat of 9.9% vs 2.5%, and higher fasting insulin. Adjusting for fat cell size cut the insulin difference in half. 4. Lean and young. Among 482 lean young adults, insulin resistance was 2 to 3 times more common in Asian Indians than in any other group. The men had about twice the liver fat of white men. 5. It starts in childhood. South Asian children aged 8 to 11 in Britain were not heavier than white children, but their fasting insulin was 53% higher, with similar blood glucose. My view: fat cells can only store so much. When they are full, they become insulin resistant and release more fat into the blood, and that fat ends up in the liver and muscle. Insulin rises to compensate. South Asians appear to reach that limit at a lower body weight. For a South Asian person, a normal BMI does not mean normal metabolism. Fasting insulin, waist size and liver fat say more than weight.