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It's Time to Do Away with the BMI

By: Leah Fattor

The Body Mass Index (BMI) is treated today as a useful tool to measure a person’s health: its calculations clearly outline healthy weight vs. unhealthy weight, so health professionals can quickly and accurately measure someone’s fatness. However, the BMI was not created as a measure of health on the individual level, and our over-reliance on the BMI may in fact be harming health, especially that of women and people of color.

History of The BMI

The BMI was invented over 200 years ago by academic Adolphe Quetelet who studied astronomy, mathematics, statistics, and sociology. He was not any sort of health professional, nor did he study any type of medicine. Quetelet created the BMI as part of his mission to identify l’homme moyen, or “the average man,” who he believed would represent a social ideal (Gibson). He derived the formula for the BMI based solely on the size and measurements of French and Scottish male conscripts, i.e. the Index was created by and for white male Europeans. His index, originally known as Quetelet’s Index, was intended only as way to measure populations, and he did not in fact plan it to be a measure of body fat, build, or health. Much of Quetelet’s work including l’homme moyen went on to be used as justification for scientific racism and eugenics (Your Fat Friend).

Quetelet’s index wasn’t reappropriated as the BMI until the 1970s. In the early 20th century, physicians began using life insurers’ rating tables as a means of evaluating a patient’s weight and health. These tables, however, were deeply flawed in that they relied on often-inaccurate self-reported data, many did not factor in age, and methods of determining weight varied widely. In addition, the tables were based only on people who had the means and ability to purchase life insurance, which meant mostly white men and women (Your Fat Friend).

In the 1970s, due to medical science’s desire for a more effective measure of weight, Ancel Keys and fellow researchers set to determine the best of existing measures of body fat. They conducted a study on 7,500 men from the United States, Finland, Italy, Japan, and South Africa. Though they studied mostly white men, they did study Japanese and Bantu men; however, the authors noted that most of their findings were not applicable or representative of the Bantu men (Your Fat Friend).

The method that Keys and his colleagues found worked the best? Quetelet’s Index, which they renamed the Body Mass Index (BMI). They found that the BMI was the best method compared to water displacement and the use of skin calipers, with “best” indicating that it was able to correctly diagnose obesity only 50% of the time. And, in 2011, the Journal of Obstetrics and Gynecology found that percentage to be even less for Black, white, and Hispanic women (Your Fat Friend).

Nonetheless, the BMI stuck. In 1995, the National Institutes of Health (NIH) revised their definition of “obesity” to be tied to individual patients’ BMIs. In 1998, NIH changed the definitions of “overweight” and “obese,” substantially lowering the bar to be medically considered fat (Your Fat Friend).

Why We Need to Ditch the BMI

Because the BMI was never designed as an individual measurement, was designed only for white men, and is only accurate 50% of the time or less, the BMI is not a good indicator of health or fatness for many groups of people. For example. researchers found that 21 million Americans were classified as “normal” by the BMI, but were in fact unhealthy, while another 54 million Americans were classified as “overweight” or “obese” but were actually healthy (Brazier).

If you fall into one of the following categories, your BMI is most likely not a good indicator of your overall health and/or true obesity level:

Black People: According to studies published by the Endocrine Society, the BMI overestimates fatness and health risks in Black people (The Endocrine Society). The BMI may also cause health professionals to over-attribute weight as a cause of diabetes, high cholesterol, and more without taking into account how chronic stress, economic inequality, and institutionalized racism affect Black people’s health in America (Gibson).

Asian People: The World Health Organization states that the BMI underestimates health risks for Asian communities, i.e. Asian people may see increased health risks before their calculation qualifies them as overweight (Lemond).

Women: Because the BMI was developed based on men’s bodies, women may be at a greater health risk because of the reliance on a measurement that wasn’t designed for them (Your Fat Friend). Furthermore, women, in general, have a higher percentage of body fat that is considered healthy: 10 to 13% fat is considered healthy in women compared to 2 to 4% for men (Brazier).

Women Who are Pregnant or Nursing: Per the CDC, women who are pregnant or nursing have higher body weights and body fat percentages, so they can nourish their baby; however, as a result, they will have a higher BMI yet no increased health risk (Lemond).

Athletes: The BMI does not differentiate between muscle, bone, and fat, yet both bone and muscle have more mass. In addition, people who are very active have heavier bones and more lean muscle, resulting in higher body weights and therefore higher BMIs (Lemond). As a result, physically fit people such as athletes may be misdiagnosed as unhealthy based on their high BMI (Devlin).

Older Adults: Because the BMI does not take age into consideration, older adults may appear to have healthy BMIs despite having excessive fat and reduced muscle (Racette, et. al.). Furthermore, a meta-analysis published in The American Journal of Clinical Nutrition found that a BMI of 27 (which is considered “overweight”), is best in terms of decreased risk in mortality for people over 65, possibly because older adults with higher BMIs tend to have more muscle, which is protective in terms of overall functionality and overall immunity (Lemond).

Short People: The measurement itself, because of the way it is calculated with weight and height, also causes short people to often be told they are thinner than they are (Brazier).

Tall People: On the flip side, because of the way the BMI is calculated, tall people are often told they fatter than they are (Brazier).

Despite the very real (and high) risk of misdiagnosing someone’s health based on the BMI, medical professionals continue to use it. However, unlike in the 1970s, today we do have more scientifically sound methods to measure obesity levels, and while they happen to cost more, they are also much more accurate (Devlin). So, next time you’re at your doctor’s office, especially if you are worried about your health, make sure that you are being assessed by more than just the BMI, particularly if you belong to any of the above groups. It’s time for us to demand better when it comes to our health.