Can We Ditch the Body Mass Index as a Predictor of Health Already?

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A measure of weight divided by height squared, the “Body Mass Index”, or BMI for short, is ubiquitous. Its ranges dictate that you are of ‘normal weight’ if your BMI is between 18.5 and 25, ‘overweight’ if it is between 25 and 30, and ‘obese’ above 30. A high BMI is thought to be an indicator of high body fat, which is then used to make direct assumptions about an individual’s health and risk for various diseases.

Insurance companies allow a person’s BMI to determine their access to healthcare coverage, while doctors make life-altering medical decisions based on it and kids learn about it in school. In and of itself, the BMI is not problematic, but its usage as an individual health indicator is hurting us all, regardless of our actual “score” on its chart.

It’s time to debunk some of the typical beliefs we commonly hold about the BMI.

 

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Myth 1: The BMI measures the state of an individual’s health.

The Body Mass Index was created in 1832 by Belgian mathematician Adolphe Quetelet at the request of his government in order to quickly measure body proportions of the general population. At the time, Quetelet argued that his index (then called the ‘Quetelet Index’ until it was renamed ‘BMI’ by Ancel Keys in 1972) is only aimed at large populations’ data collection and should never be used to measure fat levels in individuals as it ignores many other key factors like age, sex, ethnicity, or muscle mass.

Quetelet was not a doctor, nor was he a physician. His expertise was rooted in statistics and, as such, he was merely trying to develop surveying tools for large populations at a time when knowledge of the human body was still rudimentary. Just as a matter of comparison, Pasteur’s germ theory of disease will only start to take hold in the late part of the 19th century, finally encouraging doctors to wash their hands between patients. That’s roughly two generations after the invention of the Quetelet Index.

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Myth 2: The BMI is an accurate predictor of health.

In 2013, researchers from the Perelman School of Medicine at the University of Pennsylvania reported once again that the BMI “does not take into account muscle mass, bone density, overall body composition, and racial or sex differences.” Its very own composition tends to make shorter people appear slightly leaner and taller people heavier. It totally ignores waist size, which is a much more accurate indicator of fat levels. It can also rank athletes (typically presenting with more muscle mass) as overweight or obese, despite limited body-fat levels. BMI values also don’t take into account the changes in fat distribution occurring naturally as we age, making us all strive for the exact same number whether we are 15 or 65.

According to the Association for Size Diversity and Health (ASDAH), “Weight and BMI are poor predictors of disease and longevity.” What’s more, a strong focus on BMI can impact individuals’ health negatively by reinforcing fat stigma, that is then internalized, and encourages poor body image and low self-esteem. The chronic stress of marginalization is generally associated with a higher risk of depression, eating disorders, and the incidence of weight cycling, also known as “yo-yo dieting”, which are known to have long-term, devastating effects on the metabolism.

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Myth 3: You can only be healthy if your BMI is under 25.

Because it was designed as a statistics tool, the Body Mass Index’s cut-off numbers between groups (underweight, normal, overweight, and obese) are widely arbitrary, slightly partisan, and not rooted in evidence. A good example of this comes from the USA. In 1998, the United States’ National Institutes of Health changed BMI guidelines to follow the World Health Organisations directives. By dropping the ‘overweight’ category from 27.8 to 25, millions of Americans virtually woke up one day in the “overweight” range although their weight was deemed “normal” the night before. Pharma companies focused on weight loss allegedly played a role in this by heavily lobbying the change in an attempt to quickly and efficiently expand their potential consumer base.

In reality, and because of the key body-composition factors overlooked by the BMI, most of the recent studies on health and weight determined that overweight people were living at least as long as, and frequently longer than, normal weight people,” as stated in Linda Bacon’s 2010 book Health at Every Size: The surprising truth about your weight. ASDAH even recognizes that “the bulk of epidemiological evidence suggests that five pounds ‘underweight’ is more dangerous than 75 pounds ‘overweight’.

Why does it still hold strong in 2019?

Firstly, healthcare practitioners, scientists, and the media all operate through the invisible lens of a certain set of cultural values, which, at least in the western world, does not encourage size diversity. Some of that fatphobic cultural ground is rooted in outdated research that believes that fat (on your body or on your plate) is bad or that humans should (and in fact can) maintain intentional control over their weight. Unfortunately, this fallacy still inspires many public policies around health and is taught in medical schools all over the world.

Additionally, the global market for weight loss and weight management was estimated at a value of $168.95 billion in 2016. When put in competition with self-acceptance and simple, non-weight-centric lifestyle practices like moving more or eating slowly, it is obvious to see how the weight-loss industry represents a much more lucrative business proposition, ranging from supplements and diet books to bariatric surgery. Why forsake an indicator that cuts a much larger part of the cake for this industry to bite into (excuse the pun)?

We need to reconsider health outside of the weight conundrum.

Next time your medical practitioner tells you that you need to lose weight based solely on your BMI, be your own advocate; ask what other metrics could be taken into consideration and whether you still fall in the same category when waist-to-hip or waist-size ratios are applied, as these appear to be better predictors of future cardiometabolic health.

Enquire about non-weight-centric ways you could strive towards improving your health, while being more inclusive of size diversity, epigenetics, lifestyle choices, positive body image, and a truly healthy relationship with food, driven more by nutritional needs as well as hunger, satiety, and pleasure cues. Find more resources here.

All ASDAH quotes extracted from the book ‘The Obesity Myth’ by Paul Campos published in 2004. 


Florence Gillet is an Eating Psychology Coach and the founder of www.beyondbodyimage.com. By opening up about her experience with eating disorder recovery as a mother of two, Florence hopes to spread awareness about pervasive fatphobia, self-acceptance at any size, mental health issues, and raising body-confident kids in a culture engulfed in body hate. 

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