What BMI systematically misses
Body Mass Index divides weight by height squared. A BMI between 25 and 29.9 indicates overweight; above 30 is classified as obese, according to WHO standard thresholds. The limitation: BMI cannot distinguish fat mass from muscle mass. A rugby player with a BMI of 28 may be in excellent health. A sedentary person with a BMI of 23 can carry significant visceral fat with real cardiovascular risk.
NHS guidance recommends pairing BMI with waist circumference as a risk indicator. Alert thresholds for the UK: above 88 cm (35 inches) for women and above 102 cm (40 inches) for men significantly increases the risk of type 2 diabetes, heart disease, and stroke -- regardless of BMI.
Calculate your BMI with the BMI calculator and your other body measurements with the body indices tool.
Waist-to-height ratio: the measurement with stronger predictive value
The waist-to-height ratio (WHtR) is considered by several large studies to be a better predictor of cardiometabolic risk than BMI. The rule: a WHtR above 0.5 indicates elevated risk, regardless of BMI. For a person who is 170 cm tall, this means a waist above 85 cm.
NICE and the WHO both recommend WHtR as a complementary measure, particularly for adults over 40 where fat redistribution to the abdomen is common even as overall body weight remains stable.
Different thresholds for Asian populations
WHO standard thresholds (overweight at BMI 25, obese at BMI 30) were calibrated on largely European populations. For East and South Asian populations, the risk of diabetes and cardiovascular disease rises at lower BMI: overweight at BMI 23 and obese at BMI 27.5, according to WHO-WPRO and the medical societies of Japan, Korea, Singapore, and India.
This distinction is not widely known but it changes the interpretation of results for a significant portion of people in multiethnic populations. If you have South or East Asian heritage, the standard BMI categories may underestimate your metabolic risk at a given weight.