Body mass index (BMI) is an estimate of body fat. It is calculated using a statistical ratio of weight and height and applied based on your sex assigned at birth.
Developed by Adolphe Quetelet over a century ago, BMI has been an important measurement for characterizing obesity at the public health level.
More recently, however, it has been challenged for its inconsistencies. BMI may misclassify rates of overweight and obesity in historically disadvantaged ethnic populations, particularly black women.
This article discusses the history of BMI, whether it discriminates against black women, and other metrics that black women can use to gain insight into their health.
Origins of BMI as a Health Indicator
In 1842, Belgian astronomer and mathematician Lambert-Adolphe-Jacques Quetelet developed the BMI to identify statistical laws in the “average man” and to observe how these manifest in the general population.
A 1968 publication of Quetelet’s work revealed that he had examined the growth, height, and weight of more than 9,000 white men, women, and children in Brussels and Belgium. He used the results to name the “laws” of growth.
These “laws” characterize changes in physical attributes—namely, height, weight, and strength—that can be expected as a person ages and develops from childhood to adulthood.
This information was then used to advance medicine. This allowed medical practitioners to identify a person based on his physical characteristics and make a reasonable estimate of his age.
It wasn’t until 1972, however, that dietician and physician Ancel Keys determined that BMI was an appropriate indicator of body fat percentage in a population.
Since then, BMI has been relied upon as a standard measure of obesity in various populations and is a key metric in the health care field.
Does BMI Discriminate Against Black Women?
Given that BMI was developed based on studies of white populations, its ability to accurately classify overweight and obesity in other populations has been questioned.
Additionally, BMI has been adapted to compare “healthy” and “unhealthy” weights. High BMI bodies have been stigmatized as “disease bodies” in both scientific literature and media messaging.
Additionally, individuals with a high BMI body mass have been characterized as lacking willpower. For people and populations who are misclassified by BMI as overweight, this can have social and medical consequences.
Factors That the BMI Fails to Consider
BMI is a weight-for-height index. While body fat is an estimate, it doesn’t take into account body composition—that is, the percentage of weight that is fat versus lean mass, such as muscle.
For example, athletes or people with a high muscle mass percentage are often misclassified as overweight due to BMI readings, even though their body fat percentage may be in the normal range.
In general, non-Hispanic black men and women have lower body fat percentages and higher muscle mass than non-Hispanic whites and Mexican Americans.
This means that the BMI index may overestimate overweight and obesity in non-Hispanic black men and women, potentially misclassifying them as “unhealthy.”
Remember: Although BMI is an effective indicator for monitoring population-level changes, it is insufficient as a single measure to assess obesity in individuals.
Is BMI Applied Differently to Black Women and People of Color?
BMI applies similarly to white, Hispanic, and black people. However, it has been adjusted for Asian populations, as it appears to reduce obesity in this group.
People of Asian descent have the “Obese to Normal Weight” body type. This means that their BMI usually falls within the normal range, but at any BMI they have a high percentage of body fat.
Therefore, the BMI scale has been adapted to their body type to accurately identify those at increased risk of type 2 diabetes, which is common in Asian populations. .
An older study suggests that ethnic differences in the body composition of the Greenland Inuit population compared to European and American white populations mean that BMI may also increase overweight and obesity in Inuit.
Racial differences in body composition among women of African descent may be a primary contributor to higher BMI rates among black women. But these differences need to be studied to determine their clinical significance.
Racism and the BMI index
A study of counties across the United States showed that structural racism—discriminatory policies that lead to health disparities and poor health outcomes among some individuals—influenced higher BMI among black people.
BMI is strongly associated with race. For example, white men have the slowest rate of weight gain, and black women are the most likely to be obese and have higher BMIs – 6% at the highest.
Furthermore, BMI can be considered inherently racist. Its metrics are based on a narrow study population of white people and do not account for differences in body composition between racial groups, but are nevertheless used to rank obesity and “health” within those groups.
Racism continues to be of scientific interest for its role in health disparities, BMI between racial and ethnic groups, and disease rates.
Alternative Health Metrics for Black Women
Accurate measures of excess body fat or obesity are important for screening tests, such as for type 2 diabetes.
Here are three health measurements other than BMI that may be more accurate for black women.
Waist Circumference
Although BMI is a good predictor of your risk of developing type 2 diabetes, it is more accurate when combined with measures of waist circumference.
Waist circumference measures abdominal fat — excess fat around the abdomen — and is an independent predictor of heart disease and type 2 diabetes risks.
Conventional recommendations suggest that waist circumference should be less than 35 inches (88 cm) in women and less than 40 inches (102 cm) in men.
However, BMI-specific waist circumference recommendations are being developed across ethnic groups to more accurately assess health risk.
Waist-to-hip Ratio (WHR)
Another measure of abdominal obesity is the waist-to-hip ratio (WHR), which is a strong predictor of metabolic risk and cardiovascular disease.
Combining this measurement with BMI provides strong insight into patterns of body fat storage and health risk.
According to an earlier World Health Organization report, an ideal WHR is less than 0.85 for women and 0.9 for men (16).
Anatomical Impediment Analysis (BIA)
Body impedance analysis (BIA) provides detailed information about body composition and can serve as a complementary measurement to BMI.
In some cases, BIA may be interchangeable with dual-energy X-ray absorptiometry—the gold standard for body composition measurement—in population studies.
Summary
BMI relates weight to height and is an estimate of body fat and disease risk, although it is not an accurate measure of body composition.
People of African descent have a lower body fat percentage and a higher muscle mass. Therefore, BMI may misclassify them as overweight or obese, as BMI does not take into account differences in body composition.
In addition, studies show that structural racism leads to higher BMIs especially among black women, potentially making BMI an unfair metric for this population.
More research is needed to clarify whether racial differences in body composition are clinically important for disease outcomes.
BMI should not be used as a stand-alone measurement. When it’s applied this way, it’s an unfair metric for black women.
Other measures, such as waist circumference, waist-to-hip ratio, and body impedance analysis, should be used to assess health risks.
