07/05/2026
I used to think BMI was rubbish
I posted a question on Facebook on Tuesday.
"Is BMI accurate?"
It got a number of replies.
Most basically saying "No" or "For most people, yeah"
As a freshly qualified PT 24 years ago, I used to knock BMI and "height-weight charts".
Primarily because other FitPros did and I assumed they were right.
And, in retrospect, because I was carrying more body fat then than I realised.
They, and others, will point out "it puts bodybuilders and rugby players down as obese".
I'd heard that so many times, I'd accepted it as truth.
But, like many things we accept, there's actually little evidence of it.
There's a couple of key questions that should be asked of that statement:
1. What percentage of the population are bodybuilders and rugby players?
2. Out of those, what percentage have an obese BMI and a none obese body fat percentage?
I'll be honest, I've struggled to find definitive answers to either of those questions.
I would imagine number one is under 10% though.
Probably under 5.
For number two I've found studies that say numbers around 15% of rugby players have an obese BMI (over 30).
And I can't imagine that every single one of them has a none obese BF% (ie: they are actually carrying a lot of body fat, not just muscle).
As for bodybuilders?
Hard to be mega accurate.
But, a quick Google suggests the Rock has a BMI of just over 30 (technically "obese").
How many people do you see on a daily basis that are built like The Rock?
None I'd guess.
They clearly exist.
But there's not all that many of them.
So it's probably safe to say the proportion of the population that are rugby players or bodybuilders and have a BMI in the obese category, and a BF% that's none obese..........
Is under 1%.
So, maybe a good question to ask when people tell you "BMI puts rugby players and bodybuilders down as obese" is........
"Are you a rugby player or bodybuilder?"
And, if they are - "Do you have an "obese" BMI and "none obese" bodyfat percentage?"
A few years ago, I number crunched every single InBody analysis we've ever done.
And I found the percentage of our members who would still be overweight on BMI if their body fat percentage dropped to the recommended ranges to be..........
0.2%.
The percentage who would still be obese?
0%.
So, whilst far from perfect, that suggests that BMI (and height - weight charts) are more accurate than we might realise and that I used to think.
Perfect?
No.
A quick and simple tool that can help most people realise where they are?
Yes.
It works for the vast majority unless they are particularly short or tall or have especially large amounts of muscle (most people don't even if they work out a lot, myself included).
Large scale studies show this again and again.
I actually created a little calculator yesterday that shows someone what their weight and BMI would be if they were at the "recommended" bodyfat percentages.
From experience they would probably be even lighter as they lose non-bodyfat weight too.
But it's interesting.
No emotion, no interpretation, just what someone's weight and BMI would be at those bodyfat percentages --> comment below or send me a DM to find out more
As always, your BMI and BF% (along with everything else) is entirely your choice.
No one should tell you what yours 'should' be.
Least of all me.
However.....
BMI isn’t perfect - but it’s probably more accurate than the story you’ve been told.
Much love,
Jon 'BMF' Hall
P.S. If you want data driven information over emotional reaction along with none judgemental support and guaranteed satisfaction, then you'll find that at comment below or send me a DM to find out more
Yesterday's blog: "Should you be eating that?" - www.facebook.com/222067851180423_1646262720840557
