Why the Body Mass Index (BMI) is Flawed & The History of its Origins
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Is the body mass index accurate? Find out below

Someone standing on a scale to measure their body mass index (BMI)

*PLEASE NOTE: this article contains a discussion of body size and weight including the term obesity in its context as a label related to BMI.* 

Many of us are likely familiar with the term BMI, which stands for Body Mass Index. But you might be wondering, is Body Mass Index (BMI) accurate? Is it outdated? Read on for more!  

The Body Mass Index (BMI) is described as a method of measuring adiposity – it is a simple calculation that takes an individuals’ height and weight and plugs it into an equation, assigning them into a category based on this number – underweight, normal weight, overweight, and obese. But you may be wondering – is the BMI accurate? Should it be used as a clinical tool?  

As you are likely aware, BMI is (unfortunately) common practice in many primary care clinics and doctors’ offices and is even introduced in high school health classes (incredibly problematic when we think about the risks of disordered eating in this population – added fuel to the fire!). But as we’ll dive into in this article, BMI was never designed to be used at an individual level, is unable to account for other body composition and lifestyle factors and is particularly harmful and inaccurate for anyone who isn’t a white male. 

Because the truth is, BMI is lazy medicine at best and harmful at worst. Most people in healthcare acknowledge some of the limitations of using BMI but fail to see just how impractical and harmful it can be. 

A Brief History on the Origins of BMI

The Body Mass Index was invented by Adolphe Quetelet, a Belgian mathematician, statistician and astronomer. Read: not a doctor or professional at all interested in health! The origins of BMI came from Quetelet’s work in trying to statistically define the characteristics of the “average man” – an attempt to categorize populations, not individuals. It’s important to note that this doesn’t refer to average in the sense that we might use today (i.e. mediocre) as is illustrated in this quote from Quetelet: 

“If the average man were completely determined, we might consider him as the type of perfection; and everything differing from his proportion or condition, would constitute deformity or disease…or monstrosity.” 

– Adolphe Quetelet, A Treatise on Man and the development of his aptitudes 

Yikes. So really, he was attempting to evaluate the anthropometric measurements of the “ideal man” and determine how much variation from this ideal existed in the population of that time. BMI was initially called “Quetelet’s Index”, and Adolphe Quetelet developed his formula for this index (weight/height2) by exclusively studying French & Scottish participants (read: white Western European males). Again, I want to emphasize that this model was designed for statistical modelling and was not intended by its creator to be used on individuals! In fact, it wasn’t even designed to measure health in any capacity, but rather an objective way of relating height and weight in populations and fitting this data onto a bell curve. 

Moving forward through history, Quetelet’s Index seemed to be lost until it resurfaced in the research of Ancel Keys in 1972. Keys renamed the formula to Body Mass Index, as we know it today. Shortly after this, in part thanks to insurance companies adopting weight classifications for determining life insurance policies, BMI became widely used by healthcare professionals at an individual level. The BMI ranges have been tightened since the 70s, resulting in more and more people being “classified” as overweight or obese.  

I would highly recommend that you click through and read this article that dives deeper into the origin story of BMI and a description of the social context to help you better understand its problematic use today. 

4 Reasons Using BMI for Individuals is Problematic: 

1. It forces all individuals to conform to Euro-centric standards.  

Given what you just learned about the origins of BMI, and the fact that its entire premise was based on the study of white European males, can you see how this measure attempts to whittle down body diversity into a one size fits all algorithm?  

Science has repeatedly demonstrated that this measure built by a white man and designed to categorize white men is inaccurate for individuals who are anything but that. For example, research has shown sex-based differences in the relationship between body fat and BMI, meaning that we need to consider body composition differences between males and females rather than applying one equation to all! 

For People of Colour, the widespread use of BMI may lead to misdiagnosis or mistreatment. Research has shown that BMI overestimates fatness and health risks for Black people, while on the other hand, BMI may underestimate health risks for Asian communities. 

2. BMI doesn’t distinguish between different types of body mass. 

While a BMI measurement has been correlated with body fat levels (as compared to other measurement methods), it cannot tell us much about an individuals’ distribution of fat mass, visceral fat, lean muscle mass, bone density, and tissue. So, for many people, this measure is (even more) inaccurate. For example, athletes who often have higher amounts of lean muscle are often classified as having a higher BMI. Individuals who have a larger frame, or higher bone density (a good thing!), can often be classified as having a higher BMI. 

3. BMI has played a role in pathologizing body sizes.    

The BMI cut-offs have played a large role in pathologizing bodies and assigning disease states to body sizes that naturally exist, even when individuals are engaging in health-promoting behaviors (moving their bodies regularly and eating FULLY – both healthyfully and soulfully). Bodies exist in a wide range of shapes and sizes, and rather than celebrating that diversity and focusing on care for each and every body, the widespread use of BMI plays a role in institutional policies that results in weight stigma and the harm associated with this. 

4. BMI ignores health promoting behaviours. 

Even some of the biggest proponents of using BMI can admit some of its limitations (as discussed in point #1). So why is it still used? The argument is often that it is a simple, quick, and inexpensive method of measurement in a doctor’s office. But you know what else is quick and simple? Asking someone about their fruit & vegetable intake, movement patterns, alcohol & smoking history. These are just a few health promoting behaviours that can tell us so much more about a person’s overall health. Because weight isn’t a behaviour. Imagine how different a doctor’s visit might look if this was the focus versus an arbitrary mathematical calculation that is inherently flawed and wasn’t designed to be used for individuals and doesn’t account for genetic diversity?!

Hopefully this article has given you some food for thought when asking the question “Is the BMI accurate?”. If you’ve been told flippantly to lose weight, without a thought given to your lifestyle or behaviours, I am deeply sorry. By equating weight with health, we take the focus away from engaging with and encouraging health promoting behaviours, which we know promote long term health. This unfair conclusion fuels weight stigma, which research has shown can lead a person to engage in more negative health behaviours such as fad dieting and weight cycling, and do far more harm for their long-term health! This is why in my practice I take a weight-inclusive approach. I am far more concerned about your health behaviours – your sleep, stress, nutrition, and movement – than I am about a number on the scale or a BMI category.

I am hopeful that tides are beginning to turn, and that we can continue to advocate for a medical system that centers these health-promoting behaviors and reduces the use of BMI as a tool (and certainly as the only tool). In fact, in June 2023, the American Medical Association voted to adopt a new policy that discourages the use of BMI as a sole marker of health and weight, and officially recognizes the historical harm it has caused 

If you want to work with a dietitian who practices from a weight-inclusive lens, I’d love to support you! Give us a call or send us a message and let’s talk about how we can help!  

Looking to heal your relationship with food and your body? Our experienced team of Dietitians can help. 

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