BMI: Is it the be all and end all?

How do you know if you’re really healthy? For some people it’s a number on a scale, or how they look in the mirror. For others, it’s how they feel when they wake up or how much energy they have at the end of the day.

Health covers everything from how we feel on the inside, to everything on the outside. One of the ways we gauge our physical wellbeing is by our body mass index (BMI). But what does it really tell us about our health, and are there better ways to assess how healthy we really are?

Your body mass index is calculated by dividing your weight in kilograms by your height in metres squared.

“Typically, we say a healthy BMI is between 18.5 to 24.9kg/m2,” explains Bupa dietitian, Rosalyn D’Angelo.

But an individual’s BMI isn’t always an accurate representation of their weight or health.

The World Health Organization (WHO) began using BMI in 1995. For 20 years, health experts believed that it was possible to estimate health risks by whether or not a patient had a healthy BMI.

But it’s not a complete picture.

BMI also tends to overestimate obesity among shorter people and underestimate it among taller people. Therefore, D’Angelo explains, BMI shouldn’t be used as a guide for adults who are very short (less than 150cm) or very tall (more than 190cm).²

“The BMI equation doesn’t look at body composition or body shape. We say that BMI is an approximate measure of your total body fat and it is better used on a population level, not to assess an individual,” says D’Angelo.

“We know that muscle is very heavy and many elite athletes who carry more muscle than your average adult would be classified as ‘obese’ by the BMI equation. But in reality they’re probably not at risk of obesity-related chronic diseases.”

BMI can also be an inaccurate measure for pregnant people, children, and older people. Ethnicity and gender are also not considered.

The BMI formula isn’t a singular measure of your health. You may need to consider some lifestyle changes even if your BMI falls in the healthy range.

“Your waist circumference is a strong predictor of your health risk,” offers D’Angelo.

She advises men should aim for a waist circumference of less than 94cm and women of less than 80cm. Men with a waist circumference above 102cm and women who are above 88cm have a substantially greater risk of poor health outcomes, including conditions such as heart disease and type 2 diabetes.¹

It’s easy to become alarmed if a BMI calculator states that you are outside the healthy range. However, there are other important factors to consider.

“It’s important to look beyond your BMI,” says D’Angelo. “There are healthy ranges set for a range of different risk factors for chronic disease.”

She lists the following as risk factors for cardiovascular disease:

• high cholesterol
• high blood glucose levels
• high blood pressure.

Talk to your GP about some easy tests that can give you a clearer picture of your overall health.

While not a perfect formula, your BMI can indicate that you need to gain or lose weight.

“Excess weight can affect you in many ways such as worsening the symptoms of asthma, increasing your risk of sleep apnoea, and extra pressure on your joints,” says D’Angelo.

D’Angelo says it’s important to stay in touch with your GP throughout life, not just when you’re sick.

“Get your screening tests and health checks done. A blood test only takes a few minutes. Prevention is much better than a cure.”