The BMI health range has been a widely used tool in the health and medical field for over 200 years. But does BMI really paint a full picture of an individual’s health? And if it’s not an accurate tool for measuring health outcomes, why do doctors use the BMI health calculator to determine if we are healthy? We have a lot to unpack. Let’s dive in!

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What is the BMI Health Range?

The Body Mass Index (BMI) estimates whether you are at a “healthy weight” for your height. To calculate BMI, divide your weight by your height squared. For example, if you weigh 80kg and your height is 1.7m, the calculation is:

80 ÷ 1.7² = 27.6.

In this case, your BMI is 27.6 kg/m², which is classified as overweight according to the BMI health range.

The BMI health ranges are:

• Underweight: Less than 18.5 kg/m²
• Healthy weight: 18.5 kg/m² – 24.9 kg/m²
• Overweight: 25 kg/m² – 29.9 kg/m²
• Obese (Class 1): 30 kg/m² – 34.9 kg/m²
• Obese (Class 2): 35 kg/m² – 39.9 kg/m²
• Obese (Class 3): 40 kg/m² and above

These BMI ranges have been a staple in health and fitness for over 200 years. But have you ever wondered where this measure of weight in relation to height actually came from?

Where did BMI come from?

In 1832, Belgian mathematician and statistician Adolphe Quetelet was conducting population studies into marriage, crime, mental illness, and mortality. He needed a quick and easy way to measure the overall health of a large group of people, and so the BMI was born.

Quetelet aimed to create a statistical measure to understand the distribution of body weight in a population and identify patterns of health and disease. Importantly, he never intended BMI to be a diagnostic tool for individual health. Instead, it was used to study and analyse population health trends.

Over time, however, healthcare professionals adopted BMI as a quick and easy screening tool to identify potential weight-related health issues in individuals.

Is BMI a good indicator of health?

One of the biggest criticisms of BMI is that it doesn’t consider important factors like muscle mass, fat distribution, bone density, and overall body composition. For example, athletes and other highly muscular individuals may be classified as ‘overweight’ or ‘obese’ based on their BMI, even though they are not at increased risk for health problems.

Imagine being told you are overweight despite being a professional bodybuilder—talk about a confidence killer.

Moreover, BMI is not particularly accurate for many populations, such as the elderly and certain ethnic groups. For instance, BMI may misrepresent body composition in the elderly, as they typically have different amounts of lean tissue and bone density than younger adults.

Additionally, BMI doesn’t distinguish between subcutaneous fat and visceral fat. It’s important to note that visceral fat (fat around the abdominal area and organs) is generally more harmful.

However, let’s not throw the baby out with the bathwater. BMI can still be a valuable tool, especially when used alongside other measures of health and fitness. For a more complete picture of your overall health, consider body composition analysis and waist circumference measurements.

3 top tips for using BMI

1. Take it with a pinch of salt

As we’ve established, BMI is not always the most accurate way of measuring health. Therefore, it’s important to consider the limitations of BMI and use it alongside other tools for the most accurate picture of your health. Waist circumference, blood cholesterol, blood pressure, cardiovascular fitness, and strength are the 5 best tools for measuring your health.

2. Consider all factors at play

If you do a lot of weight training, you will have more muscle mass than the average person. Additionally, different sexes, ages, and ethnic groups all have different body compositions. Since BMI also changes through different stages of life, try not to worry if it fluctuates!

3. Don’t let the BMI health range rule your life

It’s easy to get fixated on the number on the scales, and BMI is no different. However, there’s much more to health than just figures and measurements—the most important thing is how you feel. Your BMI being slightly above the ‘healthy’ range doesn’t necessarily mean you are unhealthy!

If you’re worried that BMI and body image are starting to take over your life, you’re not alone. Here at www.cassiebarnard.com we specialise in food freedom, intuitive eating, and body acceptance.

If you’re interested in learning more about this approach and how it can help you, get the free, on-demand video training to learn how to feel confident in your body and calm around food.

BMI is a tool that has stood the test of time, but remember, it isn’t the be-all and end-all of health and fitness.

So, the next time someone asks you about BMI, you’ll know the full story.

References

1 NHS, 2022. What is the body mass index (BMI)? NHS.com [Online] Available at: https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/

2 Karasu, S., 2016. Adolphe Quetelet and the Evolution of Body Mass Index (BMI). Psychology Today. [Online] Available at: https://www.psychologytoday.com/us/blog/the-gravity-weight/201603/adolphe-quetelet-and-the-evolution-body-mass-index-bmi

3 Batsis, J.A., Mackenzie, T.A., Bartels, S.J., Sahakyan, K.R., Somers, V.K., and Lopez-Jiminez, F., 2016. Diagnostic accuracy of body mass index to identify obesity in older adults: NHANES 1999–2004. Clinical Studies and Practice, 40, pp. 762-767. [Online] Available at: https://www.nature.com/articles/ijo2015243