No, the BMI Isn't Racist

But indulging in unscientific myths about medicine will do real harm to minority communities.

By Eleftheria Maratos-Flier, Rexford S. Ahima and Jeffrey S. Flier.

The prevalence of obesity has markedly increased in recent decades. According to the US Centers for Disease Control and Prevention, four out of every ten Americans are now classified as obese; nearly one in ten is severely obese. And as the global middle class grows, the problem is quickly spreading around the world.

Obesity is a medical issue because scientists have, over many decades, established causal links between increased body fat and a range of diseases—including diabetes, cardiovascular disease, fatty liver disease, arthritis, sleep apnea, dementia and certain cancers. Depending on the extent of obesity, the lifetime risk of an adult with obesity suffering premature death more than doubles. Although highly effective therapies that produce safe and sustained weight loss are still limited, doctors must attempt to address obesity and its complications.

And yet, this scientific consensus is increasingly coming under ideological attack. According to promoters of “fat studies,” the medical concern about obesity is rooted in an unjustified aversion to individuals who deviate from dominant beauty standards. Meanwhile, some anti-racist scholars and activists assert this “fatphobia” is also rooted in racist assumptions.

In its current issue, for example, the Scientific American presents a feature on “the racist roots of fighting obesity.” As Sabrina Strings, a sociologist who teaches at the University of California, Irvine, and Lindo Bacon claim, “the stigma associated with body weight, rather than the body weight itself, is responsible for some health consequences blamed on obesity, including increased mortality risk.” Citing these views without comment from medical scientists, the Huffington Post arrives at a stark conclusion: “The BMI is inherently racist and sexist.”

There is no doubt that obese individuals of all ethnicities are subject to discrimination and stigmatization. It is also true that the BMI has limitations as a sole indicator of health: like most medical metrics, it is an imperfect predictor of the risk of serious disease or mortality, and must be combined with other information to render an individualized assessment. But the claim that the BMI should be thrown on the ash heap of medical history is nevertheless dangerously false. Far from damaging the most vulnerable, it is a crucial tool in safeguarding the health of black and other minority populations.

Doctors define obesity as an excess of body fat sufficient to cause or increase a variety of health risks. But deciding when somebody’s body weight is dangerous has, historically, proven to be far from simple. The Body Mass Index (BMI) is an attempt to address this. Proposed by an American physiologist, Ancel Keys, in 1972, the BMI is calculated from two easily obtained measurements: a patient’s height and weight. Over the years, studies have again and again shown that this metric really is a useful predictor of health outcomes. Both individuals with very low and those with very high BMIs are more likely to suffer premature death.

The initial population studies revealing a link between BMI and mortality employed data largely related to men of European descent. The metric’s critics heavily rely on this origin story to insinuate that the metric is useless, or actively damaging, when applied to other groups. But in the years since it was first introduced, the BMI has been assessed—and validated—as an indicator of serious health risks in a great variety of gender, racial and ethnic groups.

In some cases, the medical implications of the BMI can vary between populations. Studies on Asians have revealed that obesity complications occur at lower BMIs; consequently, lower BMI cut-offs for obesity are now employed in this group. There are also a good number of studies that have specifically focused on African-Americans. Their results are unambiguous: people of African descent are subject to the same medical complications of obesity observed in those of European descent. We lack convincing evidence that obese blacks face fewer dangers as a result of their obesity than similarly obese whites, or that different diagnostic standards should be employed.

In their Scientific American piece, Strings and Bacon argue that black people, especially women, are commonly over-diagnosed with obesity because of social factors like a racial bias against corpulent black individuals. There is no doubt that there are important health disparities between white and black Americans, and that these are caused by an interrelating set of social and economic injustices, including the greater obstacles African-Americans face in accessing quality health care. These factors likely contribute to a greater prevalence of obesity in blacks.

But given that obesity poses serious health risks to all Americans, including blacks, our concern should be very different from the one Strings and Bacon choose to emphasize. Rather than focusing on black patients being inappropriately diagnosed with obesity as a consequence of racism, we are most concerned that black individuals with obesity may go untreated because they do not receive quality health care or are denied effective therapies.

Like many health indices, the BMI is imperfect. But it is neither racist nor useless. If doctors become reluctant to use this important tool out of misplaced concern over its supposed racist origins, they would only succeed in harming the health of the most vulnerable minority populations—including many African-Americans.

Eleftheria Maratos-Flier is Professor of Medicine Emerita, Beth Israel Deaconess Medical Center, at Harvard Medical School. Rexford S. Ahima is Bloomberg Distinguished Professor of Medicine and Public Health, Johns Hopkins University Medical School and the Editor-in Chief of The Journal of Clinical Investigation. Jeffrey S. Flier is a Harvard University Distinguished Service Professor and the former Dean of Harvard Medical School