What is obesity and how is it measured?

Summary

This is a recorded session from Dr. Om’s 2025 course on obesity, held as a conversation with a fitness coach. It explains, in everyday language, why measuring obesity is more subtle than stepping on a scale.

It begins with the history of the body mass index (BMI) and the cut-offs used for Indians, which are lower than Western cut-offs because Indians tend to develop diabetes and heart disease at a lower weight. Using two imagined people with the same BMI, one healthy and active and one with prediabetes, fatty liver and breathlessness, he shows why BMI alone cannot decide who needs treatment.

The video explains the Y-Y paradox described by Dr. C. S. Yajnik: two men with the same BMI, one Indian and one European, had very different amounts of body fat. Indians tend to carry more fat inside the abdomen, around the organs, and this hidden fat drives most of the health risk.

That is why waist measurements matter. The video covers waist size, the waist-to-height ratio (a waist more than half your height is a warning sign), the body roundness index, and body composition tests such as DEXA scans and good-quality body fat analysers. It also explains the newer idea of clinical obesity, where excess fat is already causing problems in the body, and pre-clinical obesity, where it is a risk but has not yet caused harm, including the 2025 Indian definition.

You can check your own numbers with the BMI calculator and the waist-to-height ratio tool, and read what obesity is.