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Body Mass Index (BMI) is a simple screening tool that estimates body fat based on height and weight. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it divides weight in kilograms by height in meters squared (kg/m²). The WHO classifies BMI as: underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), and obese (≥30). While BMI is widely used in public health and clinical settings as a quick population-level indicator, it has important limitations — it doesn't distinguish between muscle and fat mass, doesn't account for body composition, age, sex, or ethnicity differences, and may misclassify athletes or elderly individuals. It's a starting point for health assessment, not a definitive diagnosis.
No — BMI overestimates body fat in muscular people. A bodybuilder with low body fat but high muscle mass may be classified as 'obese' by BMI. Athletes should use body composition measurements like DEXA scans or skinfold calipers instead.
The WHO considers 18.5-24.9 'normal weight.' However, optimal BMI varies by age, sex, and ethnicity. Some studies suggest slightly higher BMI (25-27) may be protective in older adults. Consult your doctor for personalized guidance.
Children's BMI is interpreted differently using age-and-sex-specific percentile charts (BMI-for-age). A BMI of 22 means different things for a 10-year-old versus a 30-year-old.
BMI is free, instant, and requires only height and weight — making it practical for screening large populations. More accurate measures (DEXA, hydrostatic weighing) are expensive and time-consuming. BMI correlates well with health risks at the population level.
Waist circumference (>102cm men, >88cm women indicates risk), waist-to-hip ratio, body fat percentage, and blood pressure are all more informative than BMI alone for assessing health risk.