Obesity Recognition: When Numbers Fail, Biology Speaks

Dr Nitin Kapoor and Dr Sanjay Kalra

Obesity must be judged by biology and metabolic risk—not by the number on the weighing scale. 

The clinic offers quiet reminders that disease rarely conforms to neat definitions. A patient with a “normal” BMI may carry visceral fat, insulin resistance, and early vascular changes. Another with a higher BMI may be metabolically resilient, protected by muscle mass and favorable fat distribution. Weight, we discover again and again, is not the diagnosis. Biology is.

Percent body fat offers a sharper lens. Metabolic risk rises not because a scale crosses a threshold, but when adiposity fuels inflammation, hormonal dysregulation, and impaired metabolic pathways. Men tipping beyond ~30% body fat and women above ~42% often enter that zone where cardiometabolic risk accelerates. Meanwhile, individuals below ~18% and ~30% rarely show biochemical signs of metabolic derailment. These patterns challenge the reflexive use of BMI as the gatekeeper of obesity care.

In practice, the implication is simple: look past appearance and arithmetic. Body composition, waist circumference, clinical context, and metabolic markers matter. Obesity is a disease of adiposity and its consequences — not of size alone. As clinicians, the task is clear. See the physiology, not the silhouette. Treat the risk, not the number.

The scale is a starting point, not the truth.

(Source: Potter AW, Chin GC, Looney DP, Friedl KE. Defining overweight and obesity by percent body fat instead of body mass index. J Clin Endocrinol Metab. 2025;110(4):e1103-e1107.)