India, Sept. 11 -- Medicine for the most part has spent years defining obesity the same way, as a body mass index above 25 with a band below it called overweight. BMI is a person's weight in kilograms divided by their height in metres squared. Early last year, both were established to be irrelevant for the Indian population. An expert commission set the line for obesity at 23 and abolished "overweight" for Asian Indians altogether.

India has an estimated 101 million adults with diabetes and 136 million more whose blood sugar is high enough to be heading there. Obesity is among the biggest modifiable causes, and the threshold at which a doctor calls it obesity holds implications for who gets investigated, who gets treated, and who is told...