Is BMI used by doctors and insurance companies?

Yes, both use BMI widely despite its limitations — primarily because it's free, fast, and correlates reasonably well with health outcomes at the population level. Some insurance companies use BMI as a criterion for coverage or premiums, which is controversial given its individual-level inaccuracy.

What BMI is considered healthy?

18.5-24.9 is the standard 'normal weight' range for most adults. But context matters enormously — a muscular person at 26 BMI is healthier than a sedentary person at 23 BMI with high visceral fat. BMI is a starting point for a health conversation, not a verdict.

Understanding BMI: What It Measures and Its Limitations

What BMI Actually Measures

Body Mass Index (BMI) = Weight (kg) ÷ Height (m)². It's a quick, inexpensive screening tool that classifies weight relative to height into four categories: Underweight (<18.5), Normal weight (18.5-24.9), Overweight (25-29.9), Obese (≥30).

BMI was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a statistical measure of population health trends — not as a diagnostic tool for individuals. It doesn't distinguish between muscle and fat, and was calibrated on 19th-century European populations.

Why BMI Misclassifies Individuals

Muscular athletes: LeBron James, most NFL linebackers, and competitive bodybuilders register as "obese" on BMI despite extremely low body fat. BMI can't distinguish 220 lbs of muscle from 220 lbs of fat.
"Normal weight obesity": Someone can have "normal" BMI (18.5-24.9) but high body fat percentage — thin but metabolically unhealthy.
Ethnic differences: Asian populations show higher metabolic risk at lower BMI values; adjusted cutoffs (Asian BMI: overweight ≥23, obese ≥27.5) are recommended by WHO.
Age: Older adults may be healthier at slightly higher BMI due to bone density and muscle reserve considerations.

Better Metrics to Use

Waist Circumference is a strong predictor of metabolic disease risk, independent of BMI. Risk thresholds: Men >40 inches (102 cm), Women >35 inches (88 cm) indicate increased risk.

Body Fat Percentage directly measures what BMI proxies. Healthy ranges: Men 10-20%, Women 18-28%.

Waist-to-Height Ratio (waist ÷ height): A ratio below 0.5 indicates low cardiometabolic risk. Simple, ethnic-neutral, and more predictive than BMI for many disease outcomes.

When BMI Is Still Useful

BMI remains useful for: population health surveillance, screening large groups quickly, identifying very high or very low body weight concerns, and as one data point in a clinical assessment. The problem is when it's treated as a diagnostic label rather than one imperfect measurement among several.