Body mass index
Body mass index (BMI) is a value derived from the weight and height of an adult, serving as an indirect screening tool for body fatness and potential weight-related health conditions.[1] It is calculated using the formula \mathrm{BMI} = \frac{\mathrm{weight\ (kg)}}{\mathrm{height\ (m)}^2}, or in imperial units as \mathrm{BMI} = \frac{\mathrm{weight\ (lb)}}{\mathrm{height\ (in)}^2} \times 703.[2] This metric, originally termed the Quetelet Index, was developed in the 1830s by Belgian mathematician, astronomer, and statistician Adolphe Quetelet to describe the "average man" in population studies rather than for individual medical diagnosis.[3] BMI categorizes adults as underweight (less than 18.5), normal weight (18.5–24.9), overweight (25.0–29.9), or obese (30.0 or higher), with higher values generally indicating greater risks of conditions such as cardiovascular disease, type 2 diabetes, and certain cancers.[4] Large-scale meta-analyses of individual participant data have demonstrated a J-shaped relationship between BMI and all-cause mortality, with the lowest risks typically in the normal weight range (around 22.5–25 kg/m² among never-smokers), increasing risks for both underweight and overweight/obese categories, though the association for overweight is less pronounced than for obesity.30175-1/fulltext)[5] Despite its widespread adoption in clinical practice and public health surveillance for its simplicity and cost-effectiveness, BMI has significant limitations as a measure of adiposity or health.[6] It fails to differentiate between lean mass and fat mass, often misclassifying muscular individuals like athletes as overweight or obese, and does not account for fat distribution (e.g., visceral vs. subcutaneous), age, sex, ethnicity, or frame size, which can lead to inaccuracies in assessing individual health risks.[7][8] Systematic reviews highlight that while BMI correlates moderately with body fat at the population level, its utility diminishes for personalized assessments, prompting calls for complementary measures like waist circumference or body composition analysis.[9] Nonetheless, empirical evidence from prospective cohorts underscores BMI's value in predicting population-level mortality and morbidity trends, even amid these flaws.[10]