Is It Time We Finally Stop Using BMI To Measure Health?

It’s one of the most well-known and commonly used measurements for understanding your health and tracking progress, but  BMI has been widely challenged and criticised in recent years - and for good reason. 

Here’s everything you need to know, because there is so much power to be had when you better understand your body and quality of healthcare, and one measurement simply doesn’t give you the whole picture.

What is BMI and how do you measure it? 

BMI, or body mass index, is a standard health assessment tool that has been used for decades by healthcare practitioners in a range of medical, health and fitness settings. It was developed during the 19th century by Belgian mathematician Adolphe Quetelet as a quick way of estimating degrees of weight and obesity in any given population.

The formula involves dividing a person’s weight in kilograms by their height in metres squared, and you can easily find your BMI by popping your height and weight into an online BMI calculator. This will calculate your BMI and determine which corresponding weight category you fall into - underweight, normal, overweight, or different levels of obesity

If your healthcare professional measures your BMI and you don’t fall into the “normal” weight range, they may recommend lifestyle changes. 

What does BMI measure and what is it good for? 

Despite all the reasons why BMI can be inaccurate and problematic when it comes to measuring overall health, which we will get into shortly, there’s a reason why it’s still so widely used. Generally, when your BMI falls into the underweight or obese categories, your risk of chronic disease and early death is much greater.

Research from 2017 aimed to study risk of death related to baseline BMI in a multiracial population of 273,843 people, and found those who were underweight, overweight or obese were at increased risk of death over 30 years compared to those with a normal BMI.

Another 2014 study examined the association of BMI with all-cause and cardiovascular disease–specific mortality risks among US adults. The researchers found obese adults had at least 20% significantly higher rate of dying of all-cause or cardiovascular disease compared to those in the normal BMI range. Similar results have been found by other research from 2018 and 2015. 

Generally, there are associations between BMI categories and health risks, but the keyword here is generally. Now let’s dig into why.

When is BMI not accurate? 

Although BMI continues to be used as a common health assessment, it’s important to understand why it can be a flawed and oversimplified measurement of your health or the health of your loved ones. 

To begin with, Adolphe Quetelet developed BMI based on a very narrow population of white French and Belgian men (a group obviously not representative of the entire human race) and he actually never intended it to be a measurement linked to health.

According to the World Health Organisation, BMI can be problematic because it only considers height and weight without considering other important factors such as fat mass, muscle and bone mass, age, ethnicity, sex and lifestyle habits such as exercise. This means it ignores many fundamental aspects of health, and can over or underestimate adiposity.

The National Eating Disorders Association has also shed light on how BMI measurement programs within schools can be triggering and harmful for children and teens, especially those who currently have, have had previously, or are at risk of developing an eating disorder. The Government of Western Australia has even pointed out how there can be issues with eating-disorder patients altering their measurements when required to self-report their BMI. 

If your child learns about BMI at school or is asked to measure theirs at any stage, educating them about its origins, limitations and pitfalls can be a helpful way to encourage healthy body image and critical thinking. They might even share the wisdom with their friends!

As the CDC explains, BMI and overall health are not the same thing. Even if people have the same BMI, their level of body fat or adiposity may differ significantly, as well as their overall health status or illness. An equation based on height and weight that fails to consider other factors, simply isn’t enough to draw any individualised conclusions about a person’s health. Sure, having higher weight for your height might be associated with an increased risk of health issues and illness, but it’s definitely not a diagnosis in itself.

BMI uses the same formula and weight categories for everyone, even though:

• Men typically have more muscle mass and less fat than women 

• One kilogram of muscle is denser and takes up less space than one kilogram of fat, therefore you could be very lean and strong (you could even be a professional athlete or bodybuilder!) while falling into the overweight or obese BMI categories. You might also lead a healthy, active lifestyle and be free of disease, yet have a higher level of fat that pushes your BMI outside of the “normal” category.

• Research shows where fat is stored on your body affects your health and risk of disease. For example, a 2020 meta analysis screened 98,745 studies and found carrying weight around your middle, including measures such as waist circumference, waist-to-hip ratio and waist-to-height ratio, was significantly associated with a higher all-cause mortality risk, independent of overall adiposity. 

• When it comes to drawing conclusions about health risks, BMI weight categories do not accurately apply to all ethnicities. For example, one 2015 study showed higher body fat, metabolic issues and cardiovascular risk factors at lower BMI values in Asian versus white populations, and 2014 research also highlighted that for all Asian populations, the risk of death when underweight is significantly higher. Other ethnic groups may also be misclassified as overweight due to naturally higher levels of muscle mass, and some groups can put on more weight than others before health issues arise.

• There are cultural differences in terms of views around body size, weight and health. In some cultures, having a higher fat mass or larger body size is viewed as being healthier.

What are alternative health measurements to BMI? 

BMI is best used as a general snapshot, a starting point or as one of many tools when assessing a person’s health and providing accurate, individualised and high-quality care.

Other important measurements and tests include waist circumference or waist-to-hip ratio, blood pressure, resting heart rate, body fat percentage, cholesterol, blood sugar, insulin, levels of hormones, vitamins and minerals, and so on.

Beyond these basic health indicators, there are other factors that should be taken into consideration when building a picture of health, such as gender, ethnicity, age, mental wellbeing, lifestyle choices, stress, medications, living environment and available resources. 

If your health practitioner calculates your BMI and provides health advice based solely or primarily on this measurement, it’s a great idea to speak up or consider seeking a second opinion or changing provider.

Moral of the story - BMI is a small snapshot, not a gold standard health measurement. So, if this is the year you decide to never check yours ever again and focus on other health indicators instead, power to you!