Invented 200 years ago by an astronomer, BMI as a measure of weight and health has long been controversial – and now the American Medical Association agrees
The American Medical Association is no longer recommending the use of BMI (body mass index) as a measure of health and weight, after years of controversy and criticism around the metric. Last week, the AMA voted to adopt a new policy which recognises not only the limits of BMI as an “imperfect measure” of health, but also its “historical harm” and “use for racist exclusion”. Instead, the association, which is one of the largest medical groups in the US, now recommends alternative measures for diagnosing obesity – in conjunction with BMI – be used in clinical settings.
“For the longest time, I’ve been in this emperor-has-no-clothes situation, where I just couldn’t understand why really smart physicians continue to rely on something that was so clearly flawed,” A. Janet Tomiyama, a professor of psychology at UCLA who has studied BMI, told the New York Times in response to the news. The new policy also advises against the use of BMI in diagnosing eating disorders, saying it is “problematic” because “it does not capture the full range of abnormal eating disorders”.
The BMI calculation takes someone’s weight in kilograms and divides it by the square of their height in metres. It then tells you if you are ‘underweight’, ‘healthy’, ‘overweight’ or ‘obese’. The metric was invented in 1832 by Adolphe Quetelet, a Belgian astronomer and mathematician, and was adopted by governments around the world beginning in the 1980s as a way to determine the health of the population.
The problem with this, however, was that Quetelet’s calculation was intended as a method to discover the “average man” (l’homme moyen) rather than someone’s individual health (Quetelet was, after all, not a doctor). He used BMI to define what was ‘normal’ and, since the participants of the original study were all white European men, this was only ‘normal’ for a very specific group of people. A healthy weight changes, however, depending on your race, gender and age. For example, Polynesians are generally healthier at a higher weight range, as are people over 65. Studies have also found that BMI overestimates fatness and health risks for Black people and underestimates health risks for Asian communities.
BMI also does not distinguish between fat, muscle and bone density, which means that using BMI, most professional athletes are classified as overweight. Nor does it take into account where on the body the fat is carried – visceral fat around your organs is considered more dangerous than other areas of the body, for example around the hips. In 2016, a study by UCLA concluded that tens of millions of people who had overweight and obese BMI scores were actually perfectly healthy. And that 30 per cent of people with “healthy” BMIs were, in fact, not healthy at all.
The recommendations from the AMA are just suggestions, rather than strict regulations that doctors must comply with. However, the association is influential in the medical community and the new policy indicates that accepted thinking around the metric and the way obesity is measured is changing. “It’s a pretty big shift,” Dr Cynthia Romero, who was involved with the development of the new policy, said to the New York Times. “Now we have to be truly more mindful and more holistic when it comes to patient care.”
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