BMI tells you whether you are healthy

What actually happened

BMI was devised in the 1830s by Adolphe Quetelet, a Belgian mathematician who was studying population averages and explicitly said it should not be used to judge individuals. It was repurposed as a personal health metric more than a century later largely because it is cheap: it needs a scale and a tape measure.

It cannot distinguish muscle from fat, which is why elite athletes are routinely classed as obese. It says nothing about where fat is distributed, and visceral fat around the organs carries very different risk from subcutaneous fat. Its cutoffs were derived largely from white European populations and misclassify risk in others, which is why some health bodies use lower thresholds for people of South Asian descent. The AMA's 2023 policy recommends using it alongside measures like visceral fat, waist circumference, and metabolic markers. BMI is still useful for comparing populations, which is what it was built for. Handing a teenager a number and a category was always a misuse.