Why Body Mass Index (BMI) Can Be Problematic for the BIPOC Community

Measuring health risks by BMI may be inaccurate for Black people and other groups of people.iStock (2)

Do you recall being asked to step on a scale during your last visit to the doctor? It’s such a common occurrence that many of us barely think about it (though some of us dread it). What you may not realize is that not only is your healthcare provider noting down your weight, but that information, along with your height, will likely be used to calculate your body mass index (BMI): a measure that moderately correlates with body fat. It’s meant to be a screening tool for a host of health conditions, but it’s hardly a one-size-fits-all solution. For some members of Black, Indigenous, and People of Color (BIPOC) communities, BMI standards can be less accurate, according to the Centers for Disease Control and Prevention (CDC) and many health researchers.

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Why BMI Is Used

BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. If your result is 18.5 or below, you are considered underweight; 18.5–24.9 means you are at a “healthy weight”; 25.0–29.9 is overweight; and 30.0 and above means you have obesity.

The reason it’s calculated at all is to help determine whether you should receive certain diagnoses or treatments, says Fatima Cody Stanford, MD, MPH, an obesity medicine doctor at Massachusetts General Hospital in Boston, who is Black. Those can include obesity, obesity-related health conditions such as type 2 diabetes and heart disease, and even some orthopedic surgeries. Your BMI can also affect how high your insurance rates are, as it is seen to be a risk indicator. But BMI isn’t meant to diagnose an unhealthy weight or another condition. Your doctor must perform additional assessments of your health to make any diagnosis.

Why BMI Is Less Accurate for Some People

BMI standards don’t correlate with fatness equally for different people. At the same BMI, those assigned female at birth tend to have more body fat than those assigned male at birth; older people have more than younger people; and athletes have less than nonathletes. People of Asian descent tend to have more body fat than white people at the same BMI; yet, for Black people, the opposite is true.

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Indeed, about 75 million adults in the United States are being misclassified as healthy or unhealthy based on their BMI alone, one study suggests. In that study group, 48 percent of the participants in the overweight category (BMI 25–29.9) were actually healthy, according to measures such as blood pressure, blood sugar, and cholesterol. So were 29 percent of people with BMIs between 30 and 34.9, and 16 percent of those with BMIs of 35 and above. Meanwhile, 31 percent of people deemed to be at a healthy weight by BMI standards were categorized as unhealthy using other medical tests. Because BMI is frequently used to determine medical care and life insurance rates, these misclassifications can be meaningful.

Further, current standards may lead Black people to be disproportionately miscategorized as having obesity and a higher risk of death. For Asians, the opposite happens, with their risk of metabolic and heart diseases more likely to be overlooked.

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Diversifying BMI

Such differences led Dr. Stanford and colleagues to propose alternative BMI standards. They were published in a 2019 letter to the editor in the Mayo Clinic Proceedings, in response to a 2004 study article in the publication that identified cutoffs in Chinese adults. “We looked at the current data from the National Health and Nutrition Examination Survey, known as NHANES, and analyzed that data for weight status, race, ethnicity, gender, and certain risk for obesity-related diseases like diabetes, high blood pressure, [and] high cholesterol, and were able to delineate what the [BMI] cutoffs would be with adjustments,” she explained. The proposed adjustments move the obesity cutoff up from the standard 30 to 31 for Black women (in her research letter, those assigned female at birth), down to 29 for Hispanic women and down to 27 for white women. That same threshold moves down to 28 for Black and Hispanic men and down to 29 for white men (again, assigned so at birth).

In other words, obesity happens for Black women at a slightly higher BMI and at a slightly lower BMI for all others. And while Stanford’s chart does not include Asian people, prior World Health Organization guidelines for Asian populations also place the obesity cutoff lower than the standard measure, at a 27.5 BMI.

To use BMI to help determine diabetes risk, Stanford’s cutoff moves a bit higher for every group; for Black women it moves up to 33. On the other hand, it moves a bit lower for everyone to determine high cholesterol risk, down to 29 for Black women.

Why? The reasons are complex, but Stanford says, “When we look at BMI charts, we haven't taken into account differences in body structure.” For instance, on average, people of different ethnicities and races tend to accumulate body fat differently, though individuals within each group can differ greatly from each other. Black people tend to have more subcutaneous fat, which lies just below the surface of the skin, in the hip, buttock and thigh regions, while white people tend to carry more fat around the organs, known as visceral fat, Stanford explains.

Of the two, visceral fat poses a higher risk to metabolic health. It is linked to insulin resistance and carries a higher risk of death. Meanwhile, subcutaneous fat carries less risk, and a few studies have suggested it can lower the risk of type 2 diabetes. Further, Black people may have less body fat and more lean muscle mass than white people at the same BMI.

Even with the proposed adjustments, Black women have the highest rate of obesity among all groups in the United States. Using current BMI standards, 44 percent are categorized as obese, compared with 29 percent of non-Hispanic white women. (Equal percentages of Black and white men have obesity: 31 percent.) The average Black woman is 187 pounds, with a BMI of 32.2, which is considered obese. Black women are also more likely to develop obesity-related conditions such as diabetes, hypertension, and high cholesterol than their white counterparts.

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But remember that BMI is a number used to diagnose obesity alone, and to identify potential risk factors for health conditions. And that “it is a population-based tool. It was not designed to be used for individuals,” says Sylvia Gonsahn-Bollie, MD, a Black obesity medicine doctor in the Washington, DC, metro area and the author of Embrace You: Your Guide to Transforming Weight-Loss Misconceptions into Lifelong Wellness. “It is very challenging at the individual level for a clinician to really say this is your healthy weight, because we're using all that bias from the population-based BMI and trying to apply it to the individual.” The first "ideal weight" tables were developed during the 1940s by the Metropolitan Life Insurance Company as a way to predict how long those who held their life insurance policies might live.

 “If we think about historically what was going on in the 1940s, there was only one demographic that was being insured by the Metropolitan Life Insurance Company, and that was white individuals,” says Stanford. The practice continued over the next few decades.

In 1972, the physiologist Ancel Keys popularized the term “body mass index” in a study article published in the Journal of Chronic Diseases, based on a calculation developed by the 19th century mathematician Lambert Adolphe Jacques Quetelet. Keys criticized the ideal-weight tables developed by insurance companies, along with other weight measures, as inadequate. He determined that BMI is a superior way to measure relative body weight, but his study population was all-male and heavily middle-aged, composed of American, European — and to a lesser degree — Japanese and Black South African men.

In 1973, with information from the Fogarty International Center Conference on Obesity at the National Institutes of Health (NIH) and NHANES data, the current BMI tables were developed, as Stanford describes in the letter to the Mayo Clinic Proceedings. The concept of an ideal — still frequently framed as “normal” — weight had persisted. In 1985, NIH began using body mass index to measure body fat, and it became widely used in medicine.

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BMI, Stigma, and the BIPOC Community

Too often, an above “normal” BMI carries a stigma with healthcare providers, Stanford says. “Most doctors, they're going to assume when they look at this measure, when it comes through your electronic health record, that you must be doing something wrong, like this is a personal failure on your part. Interestingly enough, we don't apply the same judgment if someone comes in with elevated blood pressure or elevated blood sugar.” A past study found that patients’ weights “significantly” affect how physicians perceive and treat them.

The problem is worse when you overlay race bias, she adds. “So if you have a Black woman with obesity, you know we have a lot of different potential things that are negative that are coming at you.”

Yet don’t expect the healthcare industry’s reliance on BMI to wane anytime soon. “It is challenging to kind of get away from it,” Gonsahn-Bollie says, because a lot of research is tied to using BMI as a predictor of health outcomes. “And then, a lot of our health economics are tied in to BMI, because it's just an easy tool to use,” she says. For instance, failure to report patients’ BMIs can affect the Medicare payment adjustments that a physician’s practice receives.

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Adjusting BMI and Using Other Measures to Assess Health Risks

Gonsahn-Bollie uses adjusted BMI charts such as Stanford’s as one of several tools to help determine a person’s health status. “Your healthy weight should be individualized to you. We can use these population-based tools as a starting point. So we will look at your specific, adjusted BMI based on your age, race, ethnicity, musculature, and your biological sex. We would also use your waist circumference and your body fat percentage, and then see if you have any metabolic health or obesity-related diseases.”

Waist circumference is taken with a tape measure just above the hip bones. For an adult who is biologically female and not pregnant, a waist circumference above 35 inches brings a higher risk of obesity-related diseases. For someone who is biologically male, the cutoff is 40 inches, according to the CDC.

 The International Diabetes Federation sets these cutoffs lower, and has recommended that waist circumference for women of all ethnicities be less than 31 inches; while the cutoffs for men are 37 inches for Europeans and 35 inches for Asians, South Americans, and Central Americans. Until more data is available, the cutoffs for sub-Saharan African, Middle Eastern, and Eastern Mediterranean men are the same as for European men.

Methods for estimating your body fat percentage can include taking skinfold measurements at the waist using an instrument called a caliper, or using instruments that measure fat with an electrical current, water, X-rays, or air. A “healthy” percentage of body fat is 10–22 percent for men, and 20–32 percent for women.

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Reframing How You Consider BMI as an Individual

None of this means people should be overly concerned by what the standards are, says Gonsahn-Bollie. Rather than focusing on getting to a “normal” or so-called “healthy” standard BMI or weight, she likes to work with her patients on achieving a “happy weight,” where you have reached your health goals and are able to maintain that weight happily. “That’s about self-perception and self-acceptance. It’s based on the individual. No one can tell you your happy weight.”

Helenica Yusuf, a Brooklyn, New York–based certified dietitian-nutritionist, says the BMIs of the patients in Brookdale Hospital’s diabetes prevention program are recorded because they must reach a certain threshold to qualify. But she usually discusses the measurement with patients — many of whom are Black — only if they ask about it. Otherwise, the focus is on exercising more, eating a healthier diet, and reducing their average blood sugar levels to help prevent type 2 diabetes. “In the process they lose weight, their BMI drops — not significantly — but it drops enough to say that instead of having obesity, now they're overweight. That's all right. They're healthy. Because you can have someone who looks solid but still is very healthy.”

Gonsahn-Bollie has some advice for Black people, particularly women, who worry that their healthcare provider is making inaccurate or unfair assessments of them or their health habits based on their BMIs. “First, make sure that your clinician is aware of these adjusted BMI charts. Yes, some doctors will argue that they're still investigational, but I think it speaks to the fact that we need to at least look at them. Second, have them check your waist circumference. Last, remember that you're not making excuses when you investigate. You're empowering yourself.”

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