Body Mass Index

Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. Compared relative-weight indices and concluded that weight ÷ height² (which they named the body mass index) was the best simple proxy for relative body fatness at a population level.

WHO adult cut-offs: underweight < 18.5, normal 18.5–24.9, overweight 25–29.9, obesity class I 30–34.9, II 35–39.9, III ≥ 40 kg/m². WHO also proposes additional action points at 23 and 27.5 kg/m² for many Asian populations. BMI does not measure body composition or fat distribution; interpret alongside waist circumference, clinical assessment and, in children, age- and sex-specific centile charts.