Is BMI accurate for black women?

Is BMI accurate for black women?

Body mass index (BMI) is an estimate of body fat. It is calculated using a statistical relationship between weight and height and applied based on the sex assigned at birth (1, 2).

Developed over a century ago by Adolphe Quetelet, BMI has been an important measure for characterizing obesity at a public health level.3).

More recently, however, it has been challenged for its discrepancies. BMI may misclassify rates of overweight and obesity in historically marginalized ethnic populations, particularly Black women.

This article discusses the history of BMI, whether it discriminates against Black women, and other metrics Black women can use to gain information about their health.

In 1842, the Belgian astronomer and mathematician Lambert Adolphe Jacques Quetelet developed the BMI to identify statistical laws in the “average man” and observe how these appeared in the general population (3).

A 1968 publication of Quetelet’s work revealed that he had assessed the growth, height, and weight of over 9,000 white men, women, and children in Brussels and Belgium. She used the results to name the “laws” of growth (4).

These “laws” characterized changes in physical attributes – namely height, weight and strength – that can be expected as humans age and develop from childhood to adulthood.

This information was used to advance medicine at that time. It allowed doctors to identify an individual based on his physical qualities and adequately estimate his age.

It wasn’t until 1972, however, that epidemiologist and medical nutritionist Ancel Keys determined that BMI was an adequate indicator of body fat percentage in a population (3).

Since then, BMI has been used as a standardized measure of obesity in various populations and is a key parameter in the healthcare field.


The BMI was founded in 1842 by Lambert Adolphe Jacques Quetelet to support medical advances. It was institutionalized in 1972, when nutritional epidemiologist Ancel Keys decided it was an adequate indicator of body fat percentage.

Because BMI was developed based on studies of white populations, its ability to accurately classify overweight and obesity in other populations has been questioned (5).

Additionally, BMI was adjusted to compare “healthy” and “unhealthy” weights. High BMI bodies have been stigmatized as “sick bodies” in both scientific literature and media messages (3).

Additionally, those with a high BMI were characterized as lacking willpower. For people and populations that BMI misclassifies as overweight, there may be social and medical consequences.

Factors that BMI fails to consider

BMI is an index that relates weight to height. Although it is an estimate of body fat, it does not take into account body composition, or the percentage of weight made up of fat compared to lean mass, such as muscle.5).

For example, athletes or people with higher muscle mass percentages are often misclassified as overweight due to BMI readings, even though their body fat percentage may be within normal ranges (1).

In general, non-Hispanic black men and women have lower body fat percentages and higher muscle mass than non-Hispanic whites and Mexican Americans (5, 6).

This means that BMI may overestimate overweight and obesity in non-Hispanic black men and women and potentially misclassify them as “unhealthy.”

Remember: While BMI is an effective indicator for tracking population-level changes, it is not sufficient as the sole measure for diagnosing obesity in individuals (1, 3, 5).

Is BMI applied differently to Black women and people of color?

BMI is applied equally to whites, Hispanics, and blacks. However, it has been corrected for Asian populations, as it underestimates obesity in this group (1).

People of Asian descent have a “normal weight obesity” body type. This means that their BMI is typically within the normal range, but they have a higher body fat percentage at any given BMI (7, 8).

Therefore, the BMI scale has been lowered to account for body type and to correctly identify those who are at higher risk of developing type 2 diabetes, which is prevalent among Asian populations.7, 8).

An older study showed that ethnic differences in body structure of Greenland Inuit populations compared to white European and American populations mean that BMI also likely overestimates overweight and obesity among Inuit.9).

Ethnic differences in body composition among women of African descent may contribute to higher BMI rates among Black women. But these differences must be studied to determine their clinical significance (5, 10).

Racism and BMI index

A study conducted in counties across the United States showed that structural racism – discriminatory policies that lead to health disparities and poor health outcomes in some individuals – influences higher BMI in people of color (10).

BMI is strongly correlated with race. For example, white men have the lowest trajectories for weight gain, and black women have the highest odds of developing obesity and a higher BMI – 6% higher than everyone else (10).

Furthermore, BMI can be considered inherently racist. Its metrics are based on a restricted study population of whites and do not account for differences in body composition between ethnic groups, but have nevertheless been used to classify obesity and “healthiness” in these groups.

Racism continues to be of scientific interest for the role it plays in health disparities, BMI between racial and ethnic groups, and disease rates.10).


BMI cannot distinguish body composition and often misclassifies people with higher muscle mass as overweight. It is unclear whether ethnic differences in body composition have clinical significance, but structural racism contributes to higher BMIs.

Accurate measurements of excess body fat or obesity are important for screening tests, such as for type 2 diabetes.

Here are three health metrics beyond BMI that may be more accurate for Black women.


Although BMI is a good predictor of the risk of developing type 2 diabetes, it is more accurate when combined with waist circumference measurements (11).

Waist circumference measures abdominal adiposity – excess fat around organs – and is an independent predictor of heart disease and type 2 diabetes risk (12).

Traditional recommendations indicate that waist circumference should be less than 35 inches (88 cm) in women and less than 40 inches (102 cm) in men.13).

However, BMI-specific waist circumference recommendations are being developed across ethnic groups to provide more accurate health risk assessments (13).

Waist-hip ratio (WHR)

Another measure of abdominal obesity is waist-to-hip ratio (WHR), which is a strong predictor of metabolic risk and heart disease.14).

Combining this measure with BMI yields in-depth information about body fat accumulation patterns and health risks (15).

According to an old World Health Organization report, an ideal WHR is less than 0.85 for women and 0.9 for men.16).

Body Impedance 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 measurements – in population studies (17).


Measurements of waist circumference, waist-to-hip ratio, and body impedance analysis support more accurate interpretations of BMI values ​​for health risk screening.

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 been shown to have a lower body fat percentage and higher muscle mass. Therefore, BMI may misclassify them as overweight or obese, as BMI does not account for variation in body composition.

Additionally, studies indicate that structural racism specifically leads to higher BMI among Black women, potentially making BMI an unfair metric for this population.

Further research is needed to clarify whether ethnic differences in body structure are clinically significant for disease outcomes.

BMI should not be used as a standalone measure. When applied this way, it is arguably 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.

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