‘It was more of an academic exercise’: The really old, racist and non-medical origins of the BMI


It's a simple formula: weight in kilograms divided by height in metres squared and voila, you have your body mass index — a two-digit figure that slots you into a handful of equally clear-cut boxes.

A BMI, as it's more commonly known, of below 18.5 supposedly means you're underweight, between 18.5 and 24.9 is normal, and above 30.0 is obese.

But this simplicity, many experts now say, hides the fact that determining what weight is healthy for you is far from this simple. And the BMI's easy-to-understand formula, while a handy tool for those in charge of population-wide research, is not always up to the task.

"It was more of an academic exercise back in the 1830s," dietician Tim Crowe says. But almost 200 years later, the BMI is ubiquitous — in bedrooms as people plug their dimensions into online calculators, in determining eligibility for the COVID-19 vaccine, at the doctor's office, or in the World Health Organization's definition of obesity.

So how did this formula come to define so much of what we think we know about weight and health, and why is it still in use?

The BMI's really old, non-medical and racist origins

The first thing to know about the BMI is that it was created by a Belgian mathematician — not a doctor or health practitioner.

In the 1830s, Lambert Adolphe Jacques Quetelet set out not to devise a test to quickly diagnose obesity (which was still years away from being widely perceived as a problem), but to find the "l'homme moyen" or the "average man".

His thinking went that you could take thousands of measurements, compare them, and find the ideal weight. Through calculating these samples he found that weight typically increases in relation to the square height of a person.

But there were big limitations to Quetelet's experiment. For one, all the participants were western European men. The experiment also had nothing to do with measuring individual health. 

Lambert Adolphe Jacques Quetelet created what later became the BMI in his quest to find the "average man". (Wikimedia: Library of Congress)

It wasn't until the 1970s when American physiologist and dietician Ancel Keys and a group of his colleagues promoted Quetelet's Index as the best available way to quickly screen for obesity that it became what we know today as the BMI.

But like Quetelet, the Keys study didn't account for all body types. It only measured 7,426 "healthy" men from 12 sample groups. They included American students and professionals, Italian railway workers, men from east and west Finland, Japanese farmers and fishermen, and Bantu men from South Africa (which the study itself says "could not be suggested to be a representative sample … of Bantu men in general".)

Where the BMI falls short

"If you're looking at the whole population, BMI is wonderful," Dr Crowe says. "But at an individual level, it really falls down. It only gives you a very rough measure of what someone's health could be like based on this number."

The most common example given against the BMI's effectiveness is athletes. Using the BMI, most elite athletes would be classified as overweight. That's because the test doesn't account for the difference between muscle mass, bone density and body fat.

While few of us are professional bodybuilders or weight lifters, a bigger flaw is the natural differences in body types between people of various ethnicities, genders and ages.

Athletes often have a high BMI because the formula doesn't account for muscle mass. (Pexels: Andrea Piacquadio)

When the test was devised in the 1800s it only took into account white European bodies. In the centuries since, research has revealed that a healthy weight is different for certain ethnicities. For example, Polynesians are generally healthier at a higher weight range, while for people of Asian descent, a lower BMI is seen as optimal. 

Similar caveats exist for women, who carry weight differently throughout their lifetimes, and older people. For people over-65 a higher BMI is often linked to better health because "it means you're more likely to be well-nourished", Dr Crowe says. The extra padding also provides some protection against broken bones, which can lead to fatalities in old age.

There are also people who are healthy while being clinically overweight, just as some people who fall into the "healthy" range have metabolic issues. This fact is at the heart of the growing Health at Every Size movement, which promotes acceptance of all bodies and rejects concepts like the BMI that ascribe "healthy" and "unhealthy" status without taking into account an individual's actual wellbeing.

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"[The BMI] takes someone who felt like their health was fine, the lived experience of their body as non-problematic — except for maybe other people's attitudes — they walk, talk, swim, whatever they want to do … and it tells that person 'no, you will never have health while you are like you are'," says Fiona Willer, a dietician who advises health practitioners on weight-neutral approaches to treatment.

"If we can stop labelling people as unhealthy immediately on the basis of their BMI, that would do a lot for helping those people to improve their wellbeing."

For some people, a BMI label beyond what is considered "healthy" will lead to feelings of shame — which may result in worse health outcomes if they avoid seeking treatment in the future. Alternatively, an over-reliance on the BMI as a diagnosis by health professionals can mean other issues go untreated. 

"I've lost count of the number of times I've gone to an appointment with a really simple issue like a virus … and come away feeling pretty ashamed or frustrated because the doctor chose to only focus on my BMI or weight," says Chloe Papas, a campaigner and co-organiser of A Plus market — a marketplace for pre-loved plus size clothes in Melbourne. She says this has resulted in her skipping doctor's appointments in the past to avoid the conversation. 

"For me, and for many other people in bigger bodies, the BMI can feel almost like a weapon in doctors' offices or in medical settings," she says.

"The obsession with BMI makes you feel like you aren't worthy of care … we should move towards a space where all bodies get equal access to healthcare that doesn't focus on weight or size."

So why is it still used?

About two in three Australians are classified as either overweight or obese according to the BMI. Experts say this has been exacerbated by the pandemic, with lockdowns and the push towards working from home leading to more sedentary lifestyles across the population.

"There's a pandemic of obesity," says Veronica Preda, an endocrinologist at Macquarie University's Healthy Weight Clinic. "That's been a problem for some time, but it's been exacerbated by COVID."

The Healthy Weight Clinic takes a "holistic approach" to treating obesity, which means responding to a range of health concerns — such as diabetes, blood pressure, joint issues and mental health — which differ from person to person. While the centre uses the BMI for their data, Dr Preda says it's important to move beyond a "one-size-fits-all" approach. "You've got to individualise it," she says. "It's about managing everything, not just in isolation."

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For health departments or researchers looking to measure the population's health more broadly, however, experts say the BMI is still a useful tool due to its simplicity and affordability. "It's so easy to measure," Dr Crowe says. "And what gets measured, gets counted and that's why we put so much focus on BMI even its not always the best measure."

Similarly, public health dietician Rosemary Stanton says the formula is still useful, as long as it's used in conjunction with other tests.

"By looking at lots of people, you get an overall picture that people in a particular range of the BMI are likely to have a higher or lower incidence of a lot of common diseases," she says. "It was always recognised that it's not necessarily ideal for individuals."

Dr Willer points to the early eligibility of people with obesity to receive the COVID-19 vaccine as an example of where the BMI was used positively, in this case, to screen for people who may be more vulnerable to adverse impacts from the virus. 

"We've got to remember what hat we're wearing," she says. "Are we treating people with higher body weight like they're diseased, in which case that's a problem, or are we treating people with a higher body weight as a vulnerable population to whom we need to address anything that comes up more readily."

What is the alternative?

Experts we spoke to for this story said a better test — if you need to do one at all — is waist circumference,  which is just as easy to do at home as the BMI.

To do this, health professionals measure a person at the midpoint between their bottom rib and hip bone. This should be about where your belly button is.

According to the Australian Institute of Health and Welfare, a waist circumference above 80 centimetres for women and 94 centimetres for men is associated with an increased risk of chronic conditions.

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This test is particularly useful, Dr Stanton says, because fat deposits around the waist — known as abdominal or visceral fat — are the most hazardous. "Before menopause, women can have a lot of weight on their hips, thighs, and bottom, and that fat is actually quite safe," she says. "In younger women, there's even a biological reason for it … it's an extra store of fat that women have that enables them to feed their baby during lactation."

If you find your waist measurement changing significantly, while being aware it will typically increase with age, Dr Stanton says it's something worth keeping an eye on, but "don't get yourself in a state about it".

But the bigger question is whether it's time to move away from size-based labels and weight loss goals altogether?

"A better focus is to be as healthy as you can be at whatever weight you are," Dr Crowe says. 

"If you smoke, give up smoking, if you're inactive, be more active, eating better — all of those, if you do them they may not change your weight but they will certainly improve your health."

Source: https://www.abc.net.au/news




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