Body Mass Index (BMI) is used quite heavily medically and across the board to assess body composition, however there are many limitations associated with BMI that need to be taken into consideration if it’s utilised.

What is BMI?

Basically, BMI is calculated using a person’s height and weight. The formula is BMI = kg/m2 where kg is a person’s weight in kilograms and m2 is their height in metres squared.
A BMI of 25.0 or more is considered overweight, while the healthy range is recommended to be 18.5 to 24.9.

Limitations to BMI

What you need to consider it that your weight is simply your gravitational pull to earth, but it doesn’t show what you’re made up of. For example if someone is quite heavy because they carry a lot of muscle, they will generally record a higher BMI which concludes, based on the BMI guidelines, that they would fall into the overweight or obese category which is certainly not the case.

Conversely, you might get a long distance runner for example, that may not carry a lot of muscle, may have an overall lower weight and they may be classified as anorexic or too skinny, when they’re not. They could be perfectly built for the exact sport that they’re participating or competing in.

BMI doesn’t distinguish between skeletal weight, muscle weight or fat weight. It’s just one generalised calculation, and although this equation has been used for a long time, there are serious limitations to it.

There’s more to you than just your BMI

InBody provides BMI, as many healthcare professionals still require it, and it is shown in the Calculated Analysis section. The measurements that are across the board on the other parameters that make up your weight are much more specific and important to monitor over a period of time than just the generic number that the BMI produces.

You will generally find that football players – particularly Rugby League and rugby union, are generally heavy set types of guys and girls. Although they’re quite muscular and lean, they would be considered overweight, obese or even morbidly obese based on BMI, so you can see that the accuracy is certainly not there. It’s just a generic piece of data that is used to get a broad spectrum overview of people but it’s not really precise, and it should be used with caution to make an assumption about someone.

This shows why the preciseness of InBody overrides anything on the BMI and why we do not generally refer to the BMI at all, even though it’s displayed on the result sheet. Many people can have low body fat and high muscle mass, resulting in a high BMI; we can see that they’re clearly quite lean, so the other parameters on the scan can certainly outweigh anything the BMI can provide, so it should not be the only metric that is followed.