Body Mass Index (BMI) has been used since the 1980’s to classify obesity.
Fun fact: the original version of “BMI” was actually developed in Belgium by a statistician in the 1800’s, to describe an average person and be applied to populations… it has nothing to do with health!
While BMI is simple to calculate (weight in kg divided by height in m2) we have known for a while now that it has limitations, and is maybe not the best number to chase.
Adult BMI Classification goes like this:
| < 18.5 | Underweight |
| 18.5 – 24.9 | “Normal” weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity (Class I) |
| 35.0 – 39.9 | Obesity (Class II) |
| ≥ 40.0 | Obesity (Class III) |
The major limitations of BMI are that it does not account for body composition (eg. do we have more muscle or fat), ignores ethnic and genetic variations, and does not accurately reflect an individual’s health status or risk.
Thankfully, we have a few new classification systems that address these gaps. My favourite is the Edmonton Obesity Staging System (EOSS).
I use this with my patients because it offers a more whole-person health care approach, which is what Lifestyle Medicine is all about!