BMI is useless

BMI: this podcast exposes the history of BMI (and why it’s really not fit for purpose)

Posted by for Wellbeing

In a new episode of the Maintenance Phase podcast, the hosts look back at the history of the BMI to expose its non-scientific, fat-shaming roots.

Go to the doctor, sign up at the gym or fill out a health questionnaire, and the chances are you’ll be asked about your BMI. Short for body mass index, your BMI is a calculation based on your weight divided by your height. That final number is used to categorize you into ‘underweight’, ‘normal weight’, ‘overweight’ or ‘obese’.

While the backlash against using BMI is getting louder, it’s still a pretty standard way of measuring ‘health’. But the BMI doesn’t actually tell you anything about your medical history, organ function, mental health or even how much body fat or muscle mass you carry. It literally just tells you your body’s kg-per-m². 

In a new episode of Maintenance Phase, hosts journalists Aubrey Gordon and Michael Hobbes uncovered why such a simple sum has become a standardised marker for health. The reason is pretty dark. 

Gordon rewinds to 1830 in Belgium. An astronomer and statistician named Lambert Adolphe Jacques Quetelet – who, notably, was not a medical researcher – decided he wanted to work out who the ‘average man’ was. “In his mind, the average was an ideal and what everyone should aspire to,” says Gordon. “So he started to analyse state data from France and Scotland. The data was made up exclusively of men and exclusively of white people.”

Eventually, he found the curve of the height and weight scale. “He envisioned it being used to find the size and shape of the population as a whole and he’s very clear at the time that the Quetelet scale, as it was known, was not to be used for individual diagnosis,” Gordon adds. “But by 1867 the first American life insurance company created height and weight tables with the purpose of charging fat customers more.”

To go even further, the companies weren’t following Quetelet’s guidance on what counted as ‘overweight’ or ‘obese’ – they were making the numbers up. Gordon says that the ‘overweight’ category could fluctuate by 40lbs (around 18kg) across different insurance companies. It wasn’t until the 1940s that these were standardised, and not until the 1970s that the National Institute of Health in America suggested a guideline scale for categorisation – now known as BMI.

“The way we talk about being overweight or obese now is that we assume that is tied to the onset of health complications or the increased risk of contracting certain diseases. The way that the NIH defines them was by a percentage of the population,” Gordon explains.

“This NIH definition from the 70s says that overweight people are anyone in the 85th percentile or above. Severely overweight was for people in the 95th percentile. Then they have a separate scale of measures for obesity and severe obesity, both of those are measured by skin fold thickness rather than BMI, meaning you could be classed as obese without even being overweight.

“We’re in this moment where ‘ideal weights’ are fully being invented. There are people in a room going ‘I think this is too fat’, “No, I think this is too fat’, and again, they’re being defined not relative to health risk but relative to other people.” 

In 1995, the World Health Organisation decided that BMI was going to be their standardised measure for defining weight. Given that there’s currently been no scientific research to support the BMI, it feels like an odd choice by health experts. But Gordon uncovered the reason. A report from the British Medical Journal found that the push for using BMI as a scale of health was because weight loss drug companies were sponsoring the rollout. 

“Drug companies needed to establish that weight loss is a growing concern for medicine and that a ton of people need medical intervention to help them lose weight,” Gordon says.

“The entire history of the thing is a dude who thought he was doing a population analysis and then a series of people who grabbed onto it largely for-profit motives - first insurance companies and then drug companies.”

At no point throughout this was there research that showed that those who were overweight were at more of a health risk. “It allowed the floodgates to open for researchers to ask ‘we know being fat is bad, but why exactly?’. There’s no neutrality to these questions anymore,” says Gordon. 

A woman having her bood pressure taken by a doctor
BMI: we have the ability to measure more appropriate health markers

Her co-host Hobbes then added that, given medical progression has come so far, there’s no need to allow people’s weight to dictate the health markers you can’t see. “We’re using BMI as a proxy for underlying data when the underlying data is there. If you say you don’t want people to be fat because they might have a bad resting heart rate, why not just take their resting heart rate? It’s there, you’re in a doctor’s office.”

He also added a crucial point about weight stigma and medical bias being the reasons that people in larger bodies may have more serious health complications. “There are very severe health effects that nobody looks into because they’re like ‘oh you’re fat, I’m not going to run these tests, I’m not gonna give you an MRI, I’m not gonna listen to you… There is a correlation between higher BMI and worse health and some percentage of that is the fact that life threatening illnesses in fat people do not get diagnosed.”

“Humans are diverse on every dimension, including the size they’re best suited to be. It’s not an academic issue that this was only done on white people. It’s a epidemiological issue, we’re getting shitty data by applying this to everybody.” 

And if that isn’t enough reason to focus on true health rather than aesthetics, we don’t know what is. 

Listen to The Body Mass Index episode of Maintenance Phase on Apple Podcasts

Images: Getty / Pexels

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Chloe Gray

Chloe Gray is the senior writer for stylist.co.uk's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).