Is BMI a useful number for me?

BMI is weight divided by height squared. It was designed to describe populations, not individuals, and it carries no information about what the weight is made of or where it sits. It remains useful as a first filter, and it is a poor stopping point.

What BMI cannot see

Two people with a BMI of 29 can have completely different bodies: one with substantial muscle and little visceral fat, one with low muscle mass and a large amount of fat around the liver and viscera. Visceral fat is the compartment most closely tied to insulin resistance, fatty liver and cardiovascular risk. BMI cannot detect it. Waist circumference can, in part. The National Heart, Lung, and Blood Institute identifies a waist above 40 inches in men and above 35 inches in women as marking increased risk of heart disease and type 2 diabetes, independent of the BMI category.

What the 2025 Lancet Commission changed

In January 2025 a global commission published in The Lancet Diabetes and Endocrinology proposed replacing a single BMI-based diagnosis with two categories. Preclinical obesity means excess adiposity without current organ dysfunction, a risk state. Clinical obesity means excess adiposity that is already causing dysfunction, diagnosed by BMI plus a measure of body fat such as waist circumference, waist-to-hip ratio or waist-to-height ratio, plus at least one of 18 defined obesity-related conditions in adults. The practical effect is that a diagnosis now requires evidence that something is actually wrong, rather than a number alone.

Where BMI thresholds move

BMI cut points are not the same across populations. The 2022 ASMBS and IFSO guidance recognises clinical obesity in Asian populations at a BMI above 25 kg/m2, and recommends that surgery be offered above 27.5 kg/m2. A South Asian or East Asian patient with a BMI of 27 may carry the visceral fat and metabolic risk of a European patient at 32. Older adults, people who have lost substantial muscle, and pregnant women are all groups in which BMI misleads in a different direction.

Ask for three numbers rather than one: BMI, waist circumference measured at the top of the hip bone, and a metabolic panel including HbA1c, fasting insulin or a calculated insulin resistance index, liver enzymes and lipids. Those together describe your actual risk. A BMI on its own describes a category.