The Trouble with BMI

Contributing Author: Isabelle Wilson

*Content warning: this post contains height and weight numbers and BMI category numbers. BUT my intention here is to show you why we shouldn’t put so many eggs in the BMI basket, so I hope you will keep reading!

Additionally, there is a lot to this story that goes beyond the intended scope of this post (social physics, eugenics, issues with interpreting research in general). My intention is to give you a brief insight into just some of the reasons why the BMI needs to go away forever.

I’m sure everyone knows what I’m referencing when I say BMI, but in case you need a refresher, we are talking about the Body-Mass-Index. The BMI is a measurement of exactly what it sounds like, your body mass. It’s a simple calculation of a person’s weight (in kilos) divided by the square of their height (in meters). When you visit the doctor, probably the first thing the medical assistant does is ask you to step on the scale. Most people comply (though, you don’t have to!) so the MA can document your weight and BMI. Doctors then use your BMI to “diagnose” you as “overweight” or “obese” so they can tell you to lose weight (not telling you that 95-98% of diets fail…more on that another time). I put those terms in quotes because the determination of a “normal” weight is totally flawed in and of itself (keep reading!) Let’s have some fun and learn a bit about the history of the BMI.

In 1830, a scholar by the name of Quetelet set out to find the measurements of the “average man” (this guy was fascinated by the human body, no harm there). Quetelet, by the way, was not a medical doctor, but a mathematician. He developed the formula for what we now know as BMI with the intention of analyzing a population, and even said that his measurements were never meant to be used as an individual screening tool. Quetelet was not interested in “obesity” and certainly not the individual health statuses of the men he measured. Fast forward to the 1970s, where a guy by the name of Ancel Keys revived Quetelet’s work by measuring the anthropometrics of men from a few sample groups, mostly in America and Europe (read: white people). If you haven’t stopped in your tracks yet, pause and notice so far only white men have been analyzed. No women, no kids, no people of color. Unfortunately, never in the development of BMI were women, kids, and people of color considered. Yet, we apply BMI to everyone. Maybe I’m biased because I mostly work with women and kids, but I would argue that these groups are especially vulnerable to the stigma and shame caused by being at a BMI above “normal.” Can we see why the development of the BMI is so problematic?

Next up, the body composition dilemma. The BMI equation makes no consideration for the weight of your bones and muscles, nor does it actually measure body fat. We absolutely cannot tell the health status of a person by dividing their weight by the square of their height. Individuals have varying degrees of muscle mass and bone density. A 5’8″ athlete who weighs 180 pounds will fall into the “overweight” category based simply on BMI, but when we find out they have 14% body fat, is that really a fair judgement? I see women in my office all the time who are extremely active, weight train, and eat healthful diets but continue to be hung up on their “elevated” BMI. We need to let BMI go. Some studies have found that the BMI accurately predicts “obesity” HALF the time. So 1 out of 2 people are deemed “obese” accurately. But guess what? The “obese” BMI person might be physically active 6 days a week and have perfect blood lipids, while the “normal” BMI person might have uncontrolled diabetes and a much higher risk for stroke and heart disease. Judging someone’s health on their physical appearance is about as random as the pair of socks you pull out of your sock drawer in the morning. BMI tells us nothing about a person’s genetic background, lifestyle (like smoking, drug use), and family history of chronic disease.

If you’re not uncomfortable yet, here’s a fun fact. You know those BMI cutoffs, that actually tell you what category you belong in? To refresh, 18.6-24.9 is “normal,” 25-29.9 is “overweight,” and 30 and above is “obese.” Well, originally the cutoff was about 27.5 to be considered “overweight” (and there were slightly different cut offs depending on whether you were born female or male). How did we get to 25 for everyone you may be asking? Well, there really wasn’t any scientific evidence behind the change, so your guess is as good as mine! In the midst of this change in cutoff, weight loss drugs were in the process of being approved (this was the 90s, after all). So, if “obesity” was considered a medical condition, and more and more people could be classified as “obese,” the pharmaceutical companies could make more money on their weight loss drug$. Get it?

Hopefully you’re fired up now. Why haven’t we let BMI go yet? Well, it’s a quick and easy way for doctors to screen for “obesity.” Call me high maintenance, but when it comes to my health I don’t want the convenient diagnosis. I want a thorough screening of all of the factors that decide if I’m “healthy” or not (how are my labs? What am I eating? Am I physically active? How’s my mental health? Props to the MDs I know who are asking these questions!). I am absolutely not blaming doctors here (I know I have MD, PA, and NP friends who read this!). Unfortunately, doctors don’t always make the rules. Let’s not blame the waitstaff (read: doctors) if our food comes out wrong, let’s blame the chef (read; insurance companies). Most notoriously, the Metropolitan Life Insurance Company developed the “height and weight” tables which then were popularized when doctors began using them during routine health screens, because at the time it was the “best” measure they had to screen for health. Why would insurance companies care about BMI? Because they can charge higher premiums for “overweight” and “obese” people. So, in other words, whether we are “normal” or “obese” was decided not by anyone with a medical degree, but those running insurance companies (read: NOT doctors), who were more interested in our money than our health. Awesome! These height-weight tables, by the way, did not account for age at all, an important consideration when assessing the health of an older person (if we are going to use BMI, we actually want older people to have a higher BMI. Yes, I’ve met 80 year old nursing home residents quite concerned with their BMI. Sigh).

So if BMI is so flawed, how do we measure our health and risk for chronic disease? We can look at measures that actually correspond directly to health outcomes, like waist circumference, blood lipids, and blood glucose levels. A January 2020 article published in Today’s Dietitian described waist circumference as a measure that “goes beyond simply treating all mass in the body as a homogenous pool.” It’s a better predictor of how much visceral fat someone has, the type of fat that is actually related to poorer health outcomes. We have lots of types of fat in the body, and not all are created equal. But even waist circumference should be looked at in addition to other measures mentioned above. Further, we have to move past our preconceived notions of “overweight” or “obese” people, the age old “we can’t judge a book by its cover” thinking. Weight stigma is a serious problem all around the world but definitely in the US, and I hope I’ve done my small part for today on decreasing the stigma.

To learn more about how you can practice being more weight inclusive and look at factors that go beyond body size, I encourage you to check out Health at Every Size at this link.

Works Cited

Adolphe Quetelet and the Evolution of Body Mass Index (BMI) | Psychology Today

Aubrey Gordon, Michael Hobbs, hosts. “The Body Mass Index.” Maintenance Phase. Apple Podcasts, 2021. Maintenance Phase: The Body Mass Index on Apple Podcasts

Dennett, C. “BMI vs. Waist Circumference.” Today’s Dietitian. January 2020.

Truu, M. (2022, January 1). The really old, racist, and non-medical origins of the tool we use to
measure our health. ABC News. Retrieved December 28, 2022, from

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