Weight wasn’t considered a primary indicator of health until the early 20th century, when U.S. life insurance companies began to compile tables of height and weight for the purposes of determining what to charge prospective policyholders.
Like Quetelet’s Index, however, those actuarial tables were deeply flawed, representing only those with the resources and legal ability to purchase life insurance. Weight and height were largely self-reported, and often inaccurately. And what constituted an insurable weight varied from one company to the next, as did their methods of determining weight. Some included “frame size” — small, medium, or large. Others did not. Many didn’t factor in age. Insurers were staffed by actuaries and sales agents, not medical doctors. But despite their lack of medical expertise and insurers’ inconsistent measures, physicians began to use insurers’ rating tables as a means of evaluating their patients’ weight and health. This trend reached its peak in the 1950s and 1960s.
By 1985, the National Institutes of Health had revised their definition of “obesity” to be tied to individual patients’ BMIs. And with that, this perennially imperfect measurement was enshrined in U.S. public policy.
In 1998, the National Institutes of Health once again changed their definitions of “overweight” and “obese,” substantially lowering the threshold to be medically considered fat. CNN wrote that “Millions of Americans became ‘fat’ Wednesday — even if they didn’t gain a pound” — as the federal government adopted a controversial method for determining who is considered overweight.”
That second change paved the way for a new public health panic: the “Obesity Epidemic.” By the turn of the millennium, the BMI’s simple arithmetic had become a de rigeur part of doctor visits. Charts depicting startling spikes in Americans’ overall fatness took us by storm, all the while failing to acknowledge the changes in definition that, in large part, contributed to those spikes. At best, this failure in reporting is misleading. At worst, it stokes resentment against bodies that have already borne the blame for so much, and fuels medical mistreatment of fat patients.
But more than that, science has repeatedly demonstrated that a measure built by and for white people is even less accurate for people of color — and may even lead to misdiagnosis and mistreatment. According to studies published by the Endocrine Society, the BMI overestimates fatness and health risks for Black people. Meanwhile, according to the World Health Organization, the BMI underestimates health risks for Asian communities, which may contribute to underdiagnosis of certain conditions. And, despite the purported universality of the BMI, it papers over significant sex-based differences in the relationship between body fat and the BMI. That is, because so much of the research behind the BMI was conducted on those assigned male at birth, those assigned female may be at greater health risk if their diagnosis hinges on a measurement that was never designed for them.
The science has disproved many common myths about size, health, and weight loss for years. Yet instead of recognizing the evolving and increasingly complex science around fatness, people stick stubbornly to the truisms that allow them to freely marginalize fat people.
Like phrenology and positivist criminology before it, the Body Mass Index is a product of its social context. And, even according to its biggest champions, it’s not an effective measure of fatness, much less overall health.