BMI is not an accurate measure of health. Here’s why

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BMI chart and measuring tape

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It’s no secret that we’re a society obsessed with numbers, especially when it comes to health. We track our steps, miles, hours of sleep and so much more. The health care system is no exception, since it relies on various formulas and values to measure aspects of our health.

One long-standing measurement tool in the health field is body mass index, or BMI. It was created in the 19th century and has been widely used since the 1970s, but has faced controversy in recent years, with critics saying that it’s biased, inaccurate and overall unhelpful. Plenty of people are saying it’s time for a change, and here’s why. 

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What is BMI, exactly?

BMI is a tool developed by Adolphe Quetelet in the 19th century, according to the World Health Organization. Quetelet was a mathematician, astrologer and statistician who wanted to apply probability calculus to human bodies, which is how he concluded “the weight increases as the square of the height” when he developed the Quetelet index, as BMI was first known. 

BMI wasn’t popularized until the 1970s, when the Quetelet index was used in population-based studies related to weight and was renamed body mass index. According to the WHO, in the ’70s researchers thought BMI was a good way to index potential health issues related to obesity. This was also based on reports from the Seven Countries study, which was the first study to look at how diet influences risk for heart disease. By the early 1990s, BMI was widely used and accepted after the WHO published information based on it. 

Today, medical practitioners use BMI to measure risk level for certain diseases linked to weight. The US Centers for Disease Control and Prevention says that BMI is primarily used as a screening tool to group someone into one of four weight categories: underweight, healthy weight, overweight or obese. To measure someone’s BMI, you take their weight in kilograms and divide it by the square of their height in meters. 

What’s wrong with BMI?

The problem with BMI is that it is used to assess someone’s health risk for conditions related to metabolic and other types of diseases, but at best BMI leaves out a lot of key health indicators, and at worst, it’s sexist and racist. 

“BMI is not good to use as a general health guide for several reasons,” says Dr. Aaron Hartman of Richmond Integrative & Functional Medicine. “Yes, it can be used as a general concept — but what’s really needed is individualized care for each patient that takes into account sex, stage of life and ethnicity. Saying someone is healthy, or not, based on BMI alone would not be accurate.” 

Below, Hartman and other experts share why BMI is outdated and could use a change sooner rather than later. 

It doesn’t measure body fat 

Although BMI is linked to weight and body fat, it actually does not really measure someone’s body fat, which the CDC also echoes: “[BMI] does not diagnose the body fatness or health of an individual.” For this reason, Chad Walding, doctor of physical therapy and co-founder of NativePath, says that BMI can potentially miscategorize someone as obese who is not considered clinically obese, and vice versa.

“BMI is not a super accurate way of finding a person’s true body fat percentage. Someone could be super lean but very strong and a BMI measurement would say they are obese,” says Walding. “You could also have someone whose body weight is within normal limits for their height, but they have very little muscle on their body and a whole lot of body fat. This person may show up as being of ‘normal’ weight but actually be clinically obese,” says Walding. “This limitation is that BMI only takes into account height and weight, so it’s often not the entire picture.”

BMI is not a measure of health

According to Hartman, even though BMI is now used as a screening tool by health care providers, it used to be used by insurance companies in the 1920s and ’30s to determine someone’s risk or chances of dying. “When you’re looking at general health, you’re not looking only at death for insurance policies but you’re looking at mortality, as well as morbidity — which are different gauges of death, longevity and health,” Hartman says.

First and foremost, your weight and even your level of body fat say little about your overall health. Ideally, you need much more specific metrics, like blood pressure, cholesterol or blood sugar levels, for example, to get a real picture of someone’s physical health. But the health care system has a long history of fat shaming rather than providing supportive care for all people regardless of size, which is unfair and does a disservice to people seeking care. An overemphasis on BMI contributes to this, by focusing medical professionals’ attention on weight and body fat, rather than pressing medical issues that require care.

According to Walding, other tools should be used outside of BMI to get a better read on someone’s health. “Other measurements that should be taken into consideration when painting a bigger picture of health include blood pressure, HDL and LDL cholesterol numbers, waist size, fasting blood sugar and triglycerides,” he says. 

medical scales

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It doesn’t account for sex, gender or age

Since BMI was developed in the 19th century, it’s easy to see how the tool could now be seen as outdated and out of touch, because it’s, well, old. But BMI’s problematic history goes even deeper than that. Hartman pointed out a key detail that BMI was developed for a specific, and very limited, group: largely white males. And that’s just the beginning of the problem.

“The second issue is that BMI doesn’t take gender, sex or age into account. The sex differences in BMI are notable, and BMI changes as a person ages. The BMI of a 50-year-old male and the BMI of a 50-year-old female will most likely not equilibrate,” says Hartman.

When it comes to BMI and age, Hartman says it is also easy to overlook some health issues in someone who may have a BMI that is considered healthy. “It’s natural for people to gain fat mass and lose muscle mass as they age, but it’s possible for their BMI to stay unchanging while they’re metabolically getting sick or developing a metabolic syndrome, such as diabetes,” he says. 

It’s biased against certain races

One of the biggest ways that BMI does a disservice to people is in the way it’s biased for or against certain races. Different populations tend to have different types of body composition, but because BMI was developed from research on mostly white people, it doesn’t take any of that into account.

Even the CDC mentions that BMI is a disproportionate measure for Black and Asian people, compared to white people. It states, “At the same BMI, Blacks have less body fat than do Whites, and Asians have more body fat than do Whites.”

For Black people, Hartman notes that a tendency to store fat subcutaneously (under the skin) might complicate BMI. “So an African American male may have a BMI that’s considered high — but that might actually be healthier for that individual due to the fact that their BMI for their height will actually be higher because of where they store their fat,” Hartman explains.

And for other groups like Asians, BMI again is not a fair measurement due to how they may store fat. “In the Asian population, fat is stored more around organs which is much more damaging,” he says. So someone could technically not be overweight or have a high BMI, but they are storing excess amounts of fat around vital organs. “Science has shown that fat stored around the organs is more damaging than subcutaneous fat. Having fat around your heart, for example, has a much higher risk for heart disease than having fat around your internal organs or even in your liver. BMI is not taking these things into account,” Hartman says. 

If you’re into numbers, there are other health metrics that are far more insightful than your BMI, including some that you can also measure at home. Try measuring your basal metabolic rate, blood glucose levels or heart rate variability.

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The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.

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