I had a very different blog post planned for today, but two days ago I downloaded a dance fitness app and now I’m on a rant about BMI instead. BMI (body mass index) is a measurement that people such as doctors and insurance companies use to determine whether or not someone is ‘healthy’ or ‘overweight’. The only problem is… BMI is bullshit and racist.
Body mass index was invented in the 1830s by a Belgian mathematician named Lambert Adolphe Jacques Quetelet. He was not medically trained in any way, but he was hired to produce a formula to find the ‘average man’, as long as that man was white and western European. His nonsense formula was height squared times weight, and the conclusion was that if the equation resulted in under 18.5, a person is underweight, between 18.5 and 24.9 is ‘normal’, and above 30 is ‘obese’. As you can see, it does not take into account the density and weight of muscle, bone, viscera, and fat. Nor does it account for any other body measurements, such as waist circumference or breast size. It’s an exercise in ‘correlation does not equal causation‘.
The study was re-done in the 1970s by Ancel Keys, but he still only measured men, and of the sample groups included, the study itself admitted that some of the groups ‘could not be suggested to be a representative sample’ even of the people in that group.
If you’re looking to measure the weight-to-height ratio of a bunch of people, it will certainly give you an average of sorts, but as a measure of body fat, it’s useless. Athletes often classify as ‘morbidly obese’. Whole ethnicities don’t fit into the measurements as ‘healthy’ simply because their genetics are different from white European men. Women, who carry weight differently at different points in their lives, are generally misclassified as well.
Body mass index is frequently used by doctors to explain away any problems with women’s health by telling them they’ll be fine if they just lose some weight. Fitness instructors, dieticians, and health apps use BMI to shame or scare people (often women) into paying for their classes or weight loss programs. Diet and diet pill ads prey upon internalized fatphobia to make people feel like they need the diet or the pills to be accepted in society. Active fat women are told to eat a salad or hit the gym (I’m thinking specifically about Lizzo, who is vegan and practices dance for hours every day and could out-stamina most ‘average’ men, but somehow this is still not enough for the trolls) in order to appeal to the male gaze. Many insurance premiums hinge on the measurement of a person’s BMI. The medical effects of BMI are traumatizing, and some people will avoid going to see their doctors or other health care providers because of its prevalence.
The AMA has adopted a new policy which admits there are issues with BMI as a valid clinical measurement. Quetelet himself explicitly said that BMI should NOT be used to indicate the level of fatness of an individual. So why is it that the medical world still uses it as a way to tell people that they are too fat? Because it’s easy and quick and cheap. More reliable measurements (and there are more reliable alternatives) cost more. And in a profit-based medical system like the United States has, BMI allows medical insurance companies to keep their profits high.
The next time your doctor tries to talk to you about BMI, ask them why they are using an invalid system to measure your health. And then remember that your health is not tied to your weight, and your worth is not tied to your health.