Time to say goodbye to BMI?

How did Body Mass Index (BMI) come about?

Body Mass Index or BMI was formulated in the early 1800’s, and rose to become the international standard for measuring obesity in the 1980’s.

As governments moved toward the promotion of healthy eating and exercise in the 1990s, the awareness and use of BMI as a health measure started to gain momentum.

While it’s lasted longer than many medical practices born in the early 19^th centuries, with the ever-evolving pace of change occurring in the medical profession, is it time that we say goodbye to BMI?

BMI was never intended as a measure of weight/obesity.

The BMI formula was created by a mathematician, not a physician. It was initially created to try and find the “average man”, however the experiment had nothing to do with measuring the health of an individual¹.

And, the experiment only sought data from European men, so certainly not an inclusive study.

The BMI calculation was devised at a very different time.

Nearly 200 years ago when it was created, calculators didn’t exist. Nor did computers or electronic devices. It makes sense that the calculation had to be simple to do but doesn’t mean it was accurate.

There are inherent challenges with BMI as a measure.

Physiologically, bone is denser than muscle and twice as dense as fat.

So, a person that has strong muscle tone, dense bones and has low body fat will have a high BMI.

So, a high BMI cannot be a perfect indicator of whether a person is overweight or obese. It’s possible for a very tall and fit athlete to have the same BMI as a smaller, less energetic person, and an endless number of variations in between.

Also, if BMI changes over time, without proper analysis, it is difficult to ascertain whether a change has occurred in body fat, muscle, or something else.

What about Body Fat Monitors?

Sometimes referred to as “body fat monitors”, Body Composition Analysers utilise Bioelectrical Impedance Analysis (BIA) to predict the amount of bone, muscle, and fat in a body’s composition.

The non-invasive method involves the placement of electrodes on a person’s feet hands or both. A low-level electrical current is then sent through the body, and the flow of the current is affected by the amount of water in the body.

The BIA determines the resistance to current flow as it passes through the body, and then utilises an array of equations to determine body composition.

What results is a better indicator of whether one should be concerned about their composition, stemming from the ‘body fat percentage’. The higher the body fat percentage, the more presence of fat vs. lean mass.

We utilise Body Composition Analysers at our clinic, and many of our clients find them very informative.

Other ways to determine body composition.

BIA is not the only way to determine body composition and presence of fat in the body.

Since the BMI was created, other measures such as DXA scans, skinfold callipers or even relative fat mass index (RFM) – a measure of weight to height ratio.

That is, we have many other ways of determining whether a person is overweight or obese.

So, should BMI still be used?

Approximately 2 in 3 Australians are classified as overweight or obese based on utilising BMI as a measurement². It is possible that Australia is in the middle of an epidemic, or perhaps the measurement is a little outdated.

However, the reality is that the bariatric field of medicine still requires the use of BMI for assessment since medical studies utilise this as a part of their recommendations on effectiveness.

What should I know about BMI?

Using BMI, a measure of less than 18.5 falls within the underweight range, and a BMI of 18.5 to <25 is within the healthy weight range.

To be considered overweight, your BMI must be 25.0 to <30.  If your BMI is 30.0 or higher, it falls within the obesity range.

Under the current bariatric requirements, to qualify for most weight loss surgery a patient is required to have a BMI of 30 or over.

Some surgeries require related comorbidities to be present at that BMI measurement.  Many patients without co-morbidities are eligible for surgery at a higher BMI (often ≥ 35).

As with all surgeries and medical treatments, the recommendation for surgical or non-surgical weight loss options needs to be tailored to the individual after consultation.

How does our clinic use BMI?

BMI is still utilised as an initial indicator of what treatment a patient might require, and we do provide a calculator which you can access here. However when you come into our clinic, we will not just assess your BMI.

We won’t assume that surgery is your best or only option, and we’ll discuss your expectations, lifestyle and ongoing needs before determining next steps.

The reality is that the bariatric field of medicine still requires the use of BMI for assessment since medical studies utilise this as a part of their recommendations on effectiveness.

We understand that every patient is an individual with their own needs, requirements and nuance that isn’t captured in a 200-year-old measurement.

So, until the rest of the world catches up, schedule an appointment to see us and let’s say goodbye to BMI together.

References:

¹ ABC News 2022, ‘The problem with the body mass index (BMI)’, ABC News, 2 January, viewed 18 August 2023, https://www.abc.net.au/news/2022-01-02/the-problem-with-the-body-mass-index-bmi/100728416.

² Australian Institute of Health and Welfare (AIHW) 2019, ‘Overweight and Obesity’, AIHW, viewed 18 August 2023, https://www.aihw.gov.au/reports/overweight-obesity/overweight-and-obesity/contents/summary.