If you’ve visited the doctor recently, you’re most likely familiar with the BMI. But do you actually know what it is? Where did it originate? And why it’s the go-to tool for measuring individual health at the doctors, dietitians and nurses’ offices?  

As we uncover more research examining the pros and cons of using the BMI and its questionable accuracy in measuring our health, it’s time we started asking, “is the BMI actually helping us or is it causing more harm?

Let’s explore the problem with BMI. How this humble calculation concreted itself into mainstream medicine, diet culture and see why health professionals are so reluctant to let it go. 

What is BMI?

The body mass index, or BMI, indicates someone’s body size. Calculated by dividing weight by height squared (kg/m2). In today’s healthcare system, it’s used as a quick tool to measure someone’s weight status and, more frequently, health status. 

The origins of the BMI 

The BMI, originally known as the Quetelet index, was invented by statistician Adolphe Quetelet almost 200 years ago. 

Why was the BMI invented? 

Quetelet, the inventor of the BMI, was interested in the statistical patterns of large populations. In particular, he wanted to know what the “average” white male body looked like as it aged. He developed the BMI as a tool for this pioneering cross-sectional study of human growth. It was a quick and easy way to standardise weight for any given height in large populations to derive statistical significance.

When did we start to use BMI in healthcare? 

In 1972 Ancell Keys, a physiologist (not a medical professional) renamed the Quetelet index the body mass index and stated it was the best method available for quantifying health on an individual level (although this was not its intended purpose). Since then, it’s become a standard tool to categorise bodies and their apparent health status, with everyone from doctors to insurance companies using it as a first-line health assessment. 

Why is BMI a problem? 

The BMI is an archaic tool designed to identify statistically significant patterns in large populations of white men.

The BMI was never invented to measure individual health status or designed for people of different races, sexes or body types.

However, it’s still the most widely used tool to measure body mass (and health) at an individual level. Despite its significant limitations and lack of evidence, it’s used repeatedly as a means of gatekeeping for people to access health care and medical treatments, especially for people in larger bodies. 

To add fuel to the fire in 1998, the BMI ranges shifted and reduced overnight, leading to 29 Million Americans instantly becoming overweight without actually gaining any weight. 

	BMI Range Before 1998		BMI Range After 1998
	Women	Men	Women	Men
Overweight	>27.3	>27.8	>25	>25

Maybe you’re thinking, well, they must have had a scientific and evidence-based reason for moving these ranges. Right? 

Unfortunately, not. 

It was changed to make it easier to determine statistical comparisons.

In addition, the BMI stereotypes people and reduces health to a number. While there’s evidence to show an association between a higher BMI and all-cause mortality, this is not all or nothing. Not everyone with a higher BMI is unhealthy, just as not everyone with a lower BMI is healthy. Health is nuanced, complex and multi-faceted. To use a tool like the BMI as a first line and singular measure of individual health is not only dangerous, it’s lazy.  

BMI is a form of health gatekeeping 

Every day, people are discriminated against, shamed, misdiagnosed and refused treatment because their BMI is too high. They’re refused access because a tool neglects to account for factors like age, race, gender and body composition. 

Women looking to receive fertility treatment are sent away immediately if their BMI is above 35kg/m2, despite there being inadequate evidence to show it’s dangerous for people above a BMI of 35kg/m2 to receive IVF.

People needing surgery are told to lose an arbitrary number of kg before receiving treatment.

The list goes on. 

Why do health professionals continue to use BMI despite its limitations?

It’s cheaper than a blood test, it’s embedded in our health industry, and people’s egos and reputations are on the line.  

• People don’t like to admit they’re wrong (despite evidence updating all the time) 
• While health care should be evidence-based, even health professionals have biases
• Ingrained racism and fatphobia 
• Diet companies, pharmaceutical companies, and health professionals all have a vested financial interest in continuing the narrative “fat is bad” – which the BMI helps them do 

Is BMI more harmful than helpful? 

BMI drives weight stigma and in many cases causes more harm than help. It’s leading to reductive medicine, preventing access to treatment and creating shame by labelling people into stigmatised categories. It’s not a reliable measure of individual weight or health status. It’s not a good overall indicator of your health and doesn’t consider important factors like age, race, gender and body composition. 

An alternative to BMI 

Instead of looking for an alternative to BMI, we need to acknowledge that weight is not a reliable indicator of health. 

If a person has psychological biomarkers within normal ranges, eats a balanced food intake, exercises regularly, manages stress well, and is emotionally and socially connected, they’re healthy, regardless of their weight. 

Want to learn more? 

This is just the tip of the iceberg when it comes to BMI and how it’s impacting the health of individuals. If you’d like to learn, I highly recommend exploring the resources below and working with a non-diet practitioner. 

Resources

• Origins of Quetelet Index/BMI
• BMI episode of Unpacking Weight Science podcast with Fiona Willer, PhD
• 2021 research paper