Why BMI's 200-Year-Old Formula Still Divides Doctors and Scientists

Body mass index, or BMI, remains one of the most widely used health tools today. Developed nearly 200 years ago, it offers a quick way to assess weight relative to height. Yet despite its long history, critics argue it oversimplifies how bodies differ between individuals. BMI is calculated by dividing a person's weight in kilograms by their height in metres squared. A result between 18.5 and 24.9 is classed as healthy for adults. Many doctors rely on it as a fast, low-cost method to screen large groups.

The tool, however, does not distinguish between fat and muscle. Athletes with dense muscle may register as overweight or obese, even with low body fat. Similarly, ageing affects results—muscle naturally declines with age, while fat increases, skewing BMI readings. Alternative methods exist for more precise measurements. Dual-energy X-ray absorptiometry (DEXA) scans assess bone density and body fat percentage. Electronic scanners also estimate fat levels by sending a mild current through the body. These approaches provide details BMI cannot, such as actual fat distribution. Critics highlight another flaw: BMI uses the same scale for men and women, ignoring natural body composition differences. Despite these limitations, it remains a standard first-step check in many medical settings.

BMI continues to serve as a basic health indicator for the general public. Its simplicity and low cost keep it in use, though more advanced tools offer clearer insights. For accurate assessments, doctors often combine BMI with other tests to get a fuller picture of a person's health.