6 Big Problems with BMI

Content warning: This article discusses weight and how it relates to the Body Mass Index

Many of us grew up going to the doctor’s office before the start of the new school year for our annual physicals. Besides measuring our blood pressure, height, and weight, another number that may have been thrown around in the doctor’s office is body mass index or BMI.

Simply put, BMI is an easy and inexpensive screening method to determine if a person has a healthy weight, or is classified as obese, overweight, or underweight. BMI can be calculated by taking a person’s weight, measured in kilograms, and dividing it by the square of height in meters. (You can put your calculators away and use this nifty little BMI calculator if you are interested in calculating yours.)

Before you get to calculating though, you may want to rethink BMI. There are a number of reasons why BMI is inaccurate. Here is the problem with BMI.

why is bmi inaccurate

BMI was never meant to be used as a measure of health

“Originally called the Quetelet Index, [BMI] was created by a Belgian man named Lambert Adolphe Jacques Quetelet,” explains Courtney Vickery, a Registered and Licensed Dietitian at Vickery Wellness. “Quetelet was a mathematician and his purpose in creating the equation was to be able to place people into categories in comparison to the ‘common man.’ His intention was never to use the equation as a measurement of health.”

Katherine Metzelaar, MSN, RDN, CD, and Founder/CEO of Bravespace Nutrition enlightens us further. “It was not intended for individual use. It was created from the study of white, able-bodied males intended for population analysis. It was re-branded and sold to the population at large many years after its original creation and later it was used as a way to charge people higher insurance premiums.”

BMI cannot differentiate between fat and muscle

One of the biggest problems we have with BMI is that it cannot differentiate between fat and lean muscle tissue, not to mention bone density, overall body composition, or water weight.

Take, for instance, someone who works out every day and is focused on building lean muscle mass. When their muscle mass increases, so does their overall body weight, which thereby increases their BMI even though their body may carry very little body fat.

“There is the classic example of the athlete who is classified as obese on the BMI chart due to their high muscle mass; obviously in this case the BMI interpretation is inaccurate,” shares Dr. Ellie Gordon, a clinical health psychologist who specializes in weight/eating concerns for women. “Even for non-athletes, if it is not confusing muscle with fat mass, BMI can be used or interpreted inaccurately because we often look at the number alone instead of in the context of other (more reliable) health indicators.”

And speaking of other more reliable health indicators…

BMI does not account for where we carry weight

Another problem with BMI is that it does not account for where we store fat on our bodies. Holding more weight around the hips or waist comes with higher health risks including diabetes, heart disease, and other metabolic conditions.

Lisa Richards, nutritionist and author of The Candida Diet, says, “A woman’s weight is primarily carried on her chest and thighs, which does not put her at immediate risk for chronic conditions.” Take into account a recent study where over 40,000 participants found that those with a ‘normal’ BMI could be metabolically unhealthy, while a higher BMI could be metabolically healthy. 

BMI is too simplistic

The human body is an incredibly intricate system. Employing a simple equation like BMI does not even begin to capture an accurate picture of the health of a human body. 

“It is incredibly simplistic, ” says Metzelaar. “The health of individuals is so complex and to say that an equation, that takes your weight (lbs) divided by your height (inches) squared times 703, is enough to determine one’s health status misses so much!”

BMI is just one single tool

Besides being too simplistic, BMI is also just one tool, says Sylvia Gonsahn-Bollie, M.D., body fat expert, and dual board-certified Internal Medicine and Obesity Medicine physician. “It is only meant to start the conversation.”

Metzelaar agrees, “It does not take into account bone density or muscle mass, all of which can vary from person to person. It also does not have a way to include the social determinants of health, which impact the health of an individual significantly. It also ignores behaviors. Study after study has shown us that health behaviors, regardless of weight loss, improve the overall health of the individual.” BMI also does not take into account ethnicity, race, or sex.

BMI ignores race

As we mentioned earlier, the BMI scale was originally formulated for comparing the common man, but now, with an ever-changing population, the BMI measurement is no longer relevant.

According to an article by the Washington Post, “America’s demographic fabric has dramatically shifted over the past century. People of color make up 40% of the U.S. population, and research has shown that black and white people tend to have different body compositions.” That does not even take into account the Asian population or people of Latino/Latina descent.

When BMI is applied to everyone in the country, it is as if we are comparing everyone in the country to an outdated measure or standard, which is incredibly problematic. There has to be a better way to measure health, and luckily for us, there is. Whew!

Better ways to measure health

Okay, so if BMI is not the greatest indicator of health, what is? Here are some better ways to measure our health:

  • Body fat percentage
  • Body shape in conjunction with BMI and other biometric analysis like blood work, blood pressure measurements, and strength
  • Physical activity or cardiorespiratory fitness
  • Waist circumference 
  • And of course, how you feel physically and mentally

“You cannot tell a thing about someone’s health by looking at them,” states Metzelaar. “Instead we need to be looking holistically at someone’s well being by looking at a combination of behaviors, lab work, and physical movement, but we also need to take into account things like someone’s poverty levels, access to food, connection to community, [and] the amount of stress someone experiences daily.”

Although many of us grew up hearing about BMI being the best way to calculate the ideal picture of health, there are many reasons why BMI is inaccurate. The good news is there are much better and way more accurate ways to measure our overall health and well-being—and it’s all about what works for you.

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About Ashley Martens

Ashley Martens is a Wellness Writer based in Chicago, Illinois. With a background in a digital marketing coupled with her knowledge of general nutrition and a lifelong passion for all things health, wellness, fitness and nutrition, Ashley offers a healthy alternative to traditional writing. You can learn more Ashley and her writing over at her blog, Three to Five a Day.