BMI: Is It Actually Useful? What the Science Says
BMI was invented in 1832 for population statistics. Using it for individual health assessment has serious limitations.
Body Mass Index divides weight by height squared. Simple, free, and universal — but deeply flawed for individual assessment. A muscular 200-pound athlete and a sedentary 200-pound person at the same height have identical BMIs but vastly different health profiles.
Where BMI Works
Population-level health trends. Screening tool to identify people who need further assessment. Insurance and epidemiological research. It is useful for asking whether someone might be at elevated risk and should be evaluated further.
Where BMI Fails
Athletes and muscular individuals (classified as overweight or obese despite low body fat). Elderly people (BMI underestimates fat because muscle mass has decreased). Different body compositions within the same BMI (skinny-fat individuals with normal BMI but high body fat percentage). Ethnic variations in body composition at the same BMI.
Better Alternatives
Waist circumference (under 40 inches for men, 35 for women). Waist-to-hip ratio. Body fat percentage. Waist-to-height ratio (keep waist under half your height). These all predict cardiovascular risk better than BMI for individuals.