BMI: Is it a relevant measure of health?

You may have heard of the term ‘BMI’. It stands for Body Mass Index and is a measure used to find out if you’re considered to be a healthy weight for your height.

It’s been used within our healthcare system for decades as a way to determine whether you’re at a healthy weight for your height or fall into the underweight, overweight, or obese categories.

In this post, Dr Marie Bech, Specialist Psychologist with Altum Health, explores the adequacy of the BMI as a measure of health. We also look at why we believe it to be problematic for those living with an eating disorder and what we think would be a more helpful approach to gauging a person’s health and wellbeing.

What is the BMI and how is it used?

The BMI is calculated by dividing a person’s weight by the square of their height to check whether they’re in a healthy weight range.

The concept was developed in the 19th century as a statistical tool to describe the distribution of weight across the population and determine the characteristics of the ‘average’ person. It was never intended to be used as a measure of an individual’s health. It was only in the 70s that the BMI was proposed as a means to use a person’s body weight to classify them as healthy or unhealthy. 

The BMI does have its uses, for example as a tool to help speed up the decision-making and treatment required for people at higher medical risk. These individuals will typically be at the extreme ends of the BMI scale, being severely under or overweight.  

Where the BMI is less helpful is for people in the middle part of the scale who receive an arguably arbitrary figure as a way to determine their overall health. This is in part because the different categories have been determined using mathematical means rather than by considering other health data.

The problems with the BMI

People have different body types, shapes, and sizes alongside a range of genetic differences. Yet the BMI doesn’t take into account a range of important factors such as muscle mass, bone density, and the distribution of fat, all of which play a role in determining a person’s health. 

For example, a muscly athlete might be categorised as overweight or ‘obese’ despite having low body fat. Similarly, people from different racialised backgrounds may have different body types. They might be perfectly healthy, but they could register as unhealthy on the BMI scale. 

Bear in mind too, the difference of just 100g could swing a person’s BMI into a ‘healthy’ or ‘unhealthy’ category, which could lead to an obsession with achieving a specific weight and potentially unhealthy ways of doing so. 

In addition to not providing a rounded view of a person’s health status, the BMI can make people feel judged and ashamed if they’re not within the ‘healthy’ weight category, as anything above is framed as undesirable. This can reinforce harmful stereotypes about body image. 

People living in larger bodies sometimes experience fatism and weight bias in healthcare settings because of their BMI score, despite it not being a sufficient measure on its own to determine a person’s overall health. In fact, if the message is to primarily focus on losing weight, this could further perpetuate underlying issues and contribute to the development of disordered eating. 

BMI and eating disorders

Generally speaking, being told you’re ‘underweight’ or ‘overweight’ based on a single numerical value is not a nice experience, but for those struggling with an eating disorder, it can be particularly harmful. 

As we mentioned earlier, for people at the extreme ends of the scale, BMI can be a helpful tool in alerting and getting appropriate treatment for those at higher medical risk.  

However, it’s a common misconception that individuals within a normal weight range don’t have eating disorders. Anorexia is associated with being underweight, but most people who struggle with eating disorders are a normal weight or above. 

In other words, you don’t have to be severely underweight to be suffering from an eating disorder, but the use of a BMI threshold suggests that you do. This can lead to a series of problems:

  • You don’t feel validated or deserving of help.
  • You may not be able to access the help you need because you don’t meet the criteria (BMI is one of the diagnostic criteria for Anorexia in the DSM (the Diagnostic and Statistical Manual of Mental Illnesses), which provides clinicians with guidelines for diagnosing a range of mental health illnesses).
  • Your eating disorder continues to go undiagnosed and you become even more unwell.
  • For some eating disorder sufferers, the threshold for the ‘underweight’ category on the BMI scale can even serve to encourage the eating disorder – a goal weight that one may aim to achieve or be afraid of surpassing. 

A better approach

Firstly, we encourage people not to fixate on the arbitrary figure of BMI. In some instances, it can be used as a guide to help prevent health problems and medical complications associated with the extreme ends of the weight spectrum. However, on the whole, it doesn’t capture a true picture of your overall health and can perpetuate harmful stereotypes and stigmas. 

Instead, we recommend a more holistic approach to health and wellbeing. What we mean by this is to gauge your measure of health on a selection of key markers instead. They might include your relationship with your body overall: how it feels, what it can do, how active you are, your relationship with food, and whether you rest well. 

We wouldn’t advise using an online BMI calculator, especially if you think you might be suffering from an eating disorder. Instead, please get in touch to discuss how we can help. Our licensed therapists are specialists in the treatment of eating disorders; you can book a free consultation here.

Take care, 

Dr Marie Bech

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