Commentary

When do we stop using BMI to diagnose obesity?


 

“BMI is trash. Full stop.” This controversial tweet received 26,500 likes and almost 3,000 retweets. The 400 comments from medical and non–health care personnel ranged from agreeable to contrary to offensive.

Regardless of your opinion on BMI (body mass index), this conversation highlighted that the medical community needs to discuss the limitations of BMI and decide its future.

As a Black woman who is an obesity expert living with the impact of obesity in my own life, I know the emotion that a BMI conversation can evoke. Before emotions hijack the conversation, let’s discuss BMI’s past, present, and future.

BMI: From observational measurement to clinical use

Imagine walking into your favorite clothing store where an eager clerk greets you with a shirt to try on. The fit is off, but the clerk insists that the shirt must fit because everyone who’s your height should be able to wear it. This scenario seems ridiculous. But this is how we’ve come to use the BMI. Instead of thinking that people of the same height may be the same size, we declare that they must be the same size.

The idea behind the BMI was conceived in 1832 by Belgian anthropologist and mathematician Adolphe Quetelet, but he didn’t intend for it to be a health measure. Instead, it was simply an observation of how people’s weight changed in proportion to height over their lifetime.

Fast-forward to the 20th century, when insurance companies began using weight as an indicator of health status. Weights were recorded in a “Life Table.” Individual health status was determined on the basis of arbitrary cut-offs for weight on the Life Tables. Furthermore, White men set the “normal” weight standards because they were the primary insurance holders.

In 1972, Dr. Ancel Keys, a physician and leading expert in body composition at the time, cried foul on this practice and sought to standardize the use of weight as a health indicator. Dr. Keys used Quetelet’s calculation and termed it the Body Mass Index.

By 1985, the U.S. National Institutes of Health and the World Health Organization adopted the BMI. By the 21st century, BMI had become widely used in clinical settings. For example, the Centers for Medicare & Medicaid Services adopted BMI as a quality-of-care measure, placing even more pressure on clinicians to use BMI as a health screening tool.

BMI as a tool to diagnose obesity

We can’t discuss BMI without discussing the disease of obesity. BMI is the most widely used tool to diagnose obesity. In the United States, one-third of Americans meet the criteria for obesity. Another one-third are at risk for obesity.

Compared with BMI’s relatively quick acceptance into clinical practice, however, obesity was only recently recognized as a disease.

Historically, obesity has been viewed as a lifestyle choice, fueled by misinformation and multiple forms of bias. The historical bias associated with BMI and discrimination has led some public health officials and scholars to dismiss the use of BMI or fail to recognize obesity as disease.

This is a dangerous conclusion, because it comes to the detriment of the very people disproportionately impacted by obesity-related health disparities.

Furthermore, weight bias continues to prevent people living with obesity from receiving insurance coverage for life-enhancing obesity medications and interventions.

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