All About BMI

womens healtheducation
Written By Allison Tucker, RD

How do you feel about the BMI? Do you know the history of it? And why it’s still used to this day? Allison Tucker, RD is back today with a post covering everything you need to know about the BMI! Take it away, Allison!

This post discusses weight, fatphobia, and weight loss, including specific metrics for context. At Collaborative Counseling & Nutrition, our approach is weight-neutral, focusing on helping individuals through eating disorder recovery, disordered eating challenges, and body image struggles.

All About BMI

Do you know your BMI? Do you care? Our healthcare systems certainly do.

The Body Mass Index (BMI) is a number that must tell us a great deal about our health, right? After all, it’s printed at the top of the page, right next to your name and DOB on most medical records, so it must be important!

But what does it really tell us? At its core, BMI only reflects two things: a person’s weight relative to their height. Yet, for reasons that are more historical than scientific, this simplistic metric is widely used by healthcare systems to define health.

The Origins of BMI

BMI was developed in 1832 by Lambert Adolphe Jacques Quetelet, a mathematician and astronomer—not a physician. Quetelet created the formula to establish the "normal man," a concept far removed from its current application.

Fast forward to 1972, when physiologist Ancel Keys coined the term “body mass index” after studying around 7,000 healthy (mostly white) men. Despite Quetelet’s warning that his formula wasn’t meant to analyze entire populations, BMI has become a universally recognized term.

Why is it Used? 

BMI is used to “estimate fat mass”. Why don’t we have other methods? Accurately measuring body fat is complex and prone to error, even with advanced methods like hydrostatic weighing (dunkin’ yourself in a tank of water then doing some math) or DEXA scans ($$). These are definitely not practical methods to use in your doctor’s office. 

So instead, we take a person’s height and weight and assume that will tell us everything we need to know about that person’s health and disease risk. 

What Can BMI Tell Us? Not Much. 

You’ve probably heard the argument that BMI doesn't distinguish between muscle, fat, and bone mass, which is all true. This means people with more muscle mass, like athletes, are likely to be classified as ov*rweight or ob*se, despite having a low body fat percentage. 

Because the BMI formula essentially classifies every single human being by popping out a number between, let’s say, 10-50, it goes without saying that individuals with the same BMI are going to have different health statuses! Including differences in fat and muscle mass and distribution, activity levels, nutrition status, and socioeconomic factors like income, education, and access to affordable food and healthcare. 

More importantly, the BMI imposes Eurocentric health norms that end up misclassifying individuals from diverse racial and ethnic backgrounds. For example, many Polynesians and many Black people have a proportionately lower fat mass for a given BMI compared to Caucasians, and the opposite is often true among individuals of Asian heritage, who often have a higher fat mass for a given BMI compared to Caucasians. This means people from different backgrounds have different health risks.

Assuming that these categories work for everyone—especially since BMI mainly reflects health risks for white people—ignores the differences between races and is rooted in a kind of racism that doesn't see those differences.

Is Obesity a Disease? 

Ob*sity is described as a complex medical condition, brought on by many factors, that lead to excessive body fat. In recent years, we’ve even heard more and more about ob*sity being a disease, one that is complicated and still quite misunderstood. For such a complicated medical condition, we sure have a pretty naive way of defining and diagnosing it. So, is obesity a disease? Let’s break it down. 

Some people who have chronic health conditions live in large bodies. 

Some live in smaller bodies. 

But let’s also remember…

There are individuals in larger bodies who do not have chronic health conditions. 

Probably more than we think. Some studies show nearly half of "ov*rweight" individuals and 29% of those classified as "ob*se" are metabolically healthy, while over 30% of "normal weight" individuals are not. Additionally, some research shows the risk of all-cause-mortality is similar across a wide range of BMI categories. Reducing health to a single number oversimplifies the complexity of human biology. 

How BMI Harms the General Public

Even though we know this number does not define our health, many healthcare professionals still act as though it does. Life insurance companies typically consider BMI when evaluating risk and having a higher BMI may result in increased premiums because it's seen as a potential health risk. 

Other criticisms of the BMI note that it’s not an accurate way of measuring abdominal fat, which at higher levels, is associated with chronic health conditions like cardiovascular disease, high blood pressure, and diabetes. But… even if we did have a convenient and accurate way to measure body fat, what the heck should we do with that information?

It doesn’t change the reality that weight is not a behavior, nor is fat loss.

If a person is prescribed weight loss, both fat and muscle will be lost. How do we ensure a person is healthier after they lose weight? We don’t. Especially when we remember: intentional weight loss almost always results in weight regain, and weight cycling is detrimental to cardiometabolic and mental health. 

Not only does BMI ignore critical factors like genetics, lifestyle, diet, and metabolic markers like blood pressure, cholesterol, and blood sugar, but the very use of BMI causes harmful stigma which can interfere with a patient’s opportunity to receive effective medical care. This over-medicalization of weight ties into broader societal issues, like the stigmatization of body size. Research indicates the negative impact of weight stigma and the stress it causes can be more harmful to health than living in a larger body (but more on that for a future blog post!)

BMI & Eating Disorder Recovery

First, it’s important to remember that more than 90% of people suffering from eating disorders are not underweight. In patients that have a BMI classifying them as o*erweight or ob*se, eating disorder diagnoses can be delayed by up to 9 months, compared to patients in smaller bodies. 

I can’t tell you how many individuals (who are in treatment for eating disorders) tell us their goal weight, and share they’ve determined that number based on the goal of having a “normal” BMI. Even if we didn’t account for the several flaws with BMI, we’re forgetting a super important bottom line: We lack evidence that a “normal” BMI signifies a healthy weight for an individual. It’s pretty ironic that a chart used to supposedly determine health status is creating enormous pressure to “be healthy”, quite literally at the cost of a person’s health. 

In the past, the goal of eating disorder treatment in higher levels of care was to get everyone back to the 50th percentile for weight, regardless of where they started. Setting the target weight at the average BMI can cause doctors to overlook how malnourished a patient actually is. As a result, patients might reach their target weight too quickly and get discharged before they're truly ready, increasing the likelihood of a relapse. This approach also doesn't account for the fact that some people naturally have larger bodies. If someone has always been in a higher weight range for their age, they should aim to return to that range, rather than just an average number. 

Recovery requires shifting focus away from weight and toward overall well-being and self-acceptance. Focusing on BMI can hinder the recovery process for individuals with eating disorders, where the goal should be restoring a healthy relationship with food and body. 

The Big Picture

Rather than obsessing over how we measure or estimate body fat, we want to encourage individuals to engage in health-promoting behaviors without the goal of weight loss. If you’re feeling pressure to change your body because of BMI guidelines, the dietitians and therapists at Collaborative Counseling & Nutrition are here to help! We strive to cultivate environments where individuals feel safe and supported no matter their goals. For more information, check out some of our other blog posts, “Is it Really about the Weight?” “Health vs. Weight”, and “Fatphobia: It’s Not Really About your Weight” 

Sources Used: 

Collaborative Counseling & Nutrition is an outpatient nutrition and body image counseling center, with locations in Indianapolis and Carmel, that provides compassionate, holistic eating disorder treatment. Through practicing mindfulness, intuition, and Health At Every Size, we are on a mission to help you find a true state of well-being! We take an anti-diet, weight-inclusive approach with all our clients and work to help guide you towards a way of healthy living designed by you, just for you! This post is for education purposes only and should not be used as a substitute for treatment for an eating disorder. If you are looking for a registered dietitian or therapist to assist you on your recovery journey, please reach out today!

Allison Tucker, RD

Allison is a Registered Dietitian with a Masters in Nutrition. Learn more about Allison by visiting her profile on the team page

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