If you’ve ever looked at any health article in your entire life, or watched 10 minutes of daytime TV, it’s pretty much guaranteed that you’ve heard of BMI. But what does BMI actually mean?
BMI stands for Body Mass Index.
Essentially, BMI is just a rating based on your total body weight compared to your height.
For adults over the age of 20, BMI is interpreted using standardised categories, which are the same for everyone. No different categories for men or women, for different ethnicities, for teenagers or for elderly. It’s the same thing for everyone.
For those aged between 2-20, BMI scores do take into account age and sex, however.
On the adult BMI scale:
A score under 18.5 is classed as underweight.
A score of 18.5-24.9 is classed as a healthy weight.
A score of 25-29.9 is classed as overweight.
A score over 30 is classed as obese.
The formula used to calculate BMI scores is pretty straightforward:
Weight (Kg) / Height (m)2
So what are the benefits of BMI:
- It tends to be a pretty good way to estimate fat ranges in the majority of people. Increases of BMI after a certain point has been proven to be associated with increasing medical issues
- It’s cheap to track. All you need is scales, a tape measure, and a calculator. Specific body fat measurements, such as DXA, underwater weighing, or other full body scans, can be expensive.
- BMI is simple, non-invasive to calculate and can be worked out in five minutes or less whenever you want.
In saying that, what are the downsides to using BMI?
- BMI is notoriously inaccurate when you come across people with above-average muscle mass. Body builders are classified as Obese with BMI system.
- It isn’t accurate as a predictor of total body mass in general. Women for example have a higher percentage of body fat than men at the same BMI score, purely due to basic biology.
This makes BMI a poor measurement for anyone specifically trying to reduce body fat, rather than just overall weight. Frequent gym-goers, for example, often lose fat without losing weight — as they offset their fat loss against some muscle and bone-density gain.
Which means that BMI scores aren’t necessarily the greatest thing to use when tracking your healthy weight range.
So don’t think that a BMI measurement is the final score, because it really isn’t all that it’s cracked up to be.
- Em x