AIBU to tell you that BMI doesn't apply to everyone!

[Randomuser456]

Foreword I know it's a blunt tool, etc, etc ,etc... and I DO exercise more than the average person (don't really ift heavy) but I've always thought my clothes size doesn't match my weight.

Anywho according to the Navy Body Fat formula I'm around 27-28%

A BMI extrapolation would put me at 38%. By reversing that calculation someone with my BF% is around 15kg lighter than my current weight.

Anyway just a public service announcement :)

Don't be ridiculous.
99% of the population couldn't swim 3km in one session.

Of course it is impressive (even though original poster didn't post to claim that).
Of course it contributes to all round fitness.

If it doesn't work for you your doctor will tell you. I have a very broad build, small waist, large bust and bum, and I do a lot of strength training. I'm also tall. I am indisputably obese but losing weight. My doctor has advised me to aim for 1-2 stone above the top end of the healthy BMI range for my height and weight and then consider whether I need to drop any more.

IME the ladies in my club definitely cared about racing weight, which grant it is not the same per se (but still it has been debunked).

In all of my other fitness groups day in and day out you see people asking about it.

I genuinely don't know if I look slim or not, I have a really wrapped idea now but that just comes of 30+ years of being overweight (and definitely being overweight!)

I'd never heard of the navy body weight calculator!

I just did it and it told me my body fat was 17%.

It's actually 18% as I had it checked yesterday. So not far off!

BMI is weight to height. It doesn't measure body fat.

My body fat on the navy calculator is 35pc making me 'normal weight obese'. My BMI is around 20. I guess o need to do body recomposition.
On a smart scale, my body fat isn't as bad, but isnt great either.

Where did you get it checked? I thought the only reliable way was a very expensive dexa scan MRI...

If you’re female, 28 is overweight, <25 is healthy.

Yes I'm very much aware of this... But all medical / health professionals had said that at this point losing weight won't necessarily benefit my overall health

Well, it is really. I believe they didn’t use any black people when calculating it so it isn’t exactly representative of everyone.

I don't really understand your post.

As a useful and crude way of assessing your weight, given your height, it's pretty useful.

It's only really professional level athletes who it doesn't work too well with.

What is your BMI? What is your clothes size? What's your weight and height? How much exercise and what type (eg. Distance running/weight lifting etc..) do you do? And why are you not happy with your BMI?

Yet you said this in one of your first posts. It’s not considered normal/healthy. I check mine weekly-currently 27%, so sill classified as overweight, not ‘healthy’.

Having read the full thread now, I think you are just a very unusual case. Maybe you hold lots of muscle in your legs or something! To be a size 4 and BMI 22/23 is v unusual! (I'm BMI 21 and size 12. Most people would probably be a size 10 ISH at this BMI).

I think BMI works for most of us, maybe 90% of us, as a crude measure of our weight (relative to height). But sure, there'll be some unusual cases such as yourself, where it's not helpful.

Really? I can't believe that 99% of the population couldn't do that - or equivalent running or similar, if they can't swim. But that's not really the point. Swimming 120 lengths once a week doesn't make you the sort of "athlete" for whom BMI is not relevant.

And we lack relevant information. How long does this take her? Is it inside or out? Does she stop in the course of doing it for a rest? More likely a sign of fitness if she can do it in under 1h25, outside, and without stopping but absent any other exercise - which is the impression I got from the post (otherwise why not mention it?) - this is not likely to indicate a person for whom BMI is not going to be a reasonable basic measure.

That's the problem: people have no idea what fitness is, or what an athletic body is and rationalise potentially problematic health and behaviour by saying "I go swimming once a week, therefore BMI can't reflect anything about my health, I'm one of those athletes". FAOD, I am not one of those athletes, I am mildly overweight by BMI, this accords with my appearance, fitness and general state of health (and I exercise far more than a 3km swim a week!). I need to lose some weight. I know that. That gives me a massive advantage in doing something about this. Most people (me included) find losing weight hard. It's impossible if you don't accept that you do need to lose some.

And btw, this chart shows 3km swim times
https://swimminglevel.com/swimming-times/3k-times
It also defines Beginner, novice and intermediate swimmers as:
Beginner Faster than 5% of swimmers. A beginner swimmer has started swimming and has swum for at least a month.
Novice Faster than 20% of swimmers. A novice swimmer has swum regularly for at least six months.
Intermediate Faster than 50% of swimmers. An intermediate swimmer has swum regularly for at least two years.

If the PP can't swim the average time for her swimming "level" and age (or in fact quite a bit better), that would clearly indicate someone for whom BMI is likely to be accurate IMO.

I don't believe it was based on women at all was it? So yes, in that sense it is skewed. But it is not "skewed" in the way that poster meant.

Seems to be an especially popular factoid with people it definitely does apply to though

I'm not sure there were a lot of BAME people in 1840s Belgium. And I think the NHS calculator does adjust for ethnicity and sex.

@HornungTheHelpful do you realise that according to government stats “4 out of 10 (41%) adults aged 40 to 60 in England walk less than 10 minutes continuously each month at a brisk pace.”

That’s less than 10 minutes even moderate exercise every 4 weeks. NHS recommendations say that we should be doing 150 minutes a week.

so I think that your assertion that most people could swim 3km no bother is, to say the least, optimistic!

Nope, body fat of 27% is considered healthy here's a medical journal article about it: https://pubmed.ncbi.nlm.nih.gov/8615340/

BMI of 27 is considered overweight, different things

I didn't say "no bother". I said "could do it". I don't know if the PP is swimming it in an elite 50 minutes, or taking three hours with breaks.

But the point remains - swimming 3km a week, absent lots of other exercise, which was curiously not mentioned when it would have been pertinent - is not going to mean BMI doesn't act as a good basic measure of whether or not you're carrying too much fat.

Me saying “no bother” is really what you took from my post? You know my point was that no, most people couldn’t do it. They are mostly inert.

Plus around 1/3 of adults in the UK can't swim at all, so your quoting times for the tiny minority of people who could swim 3km in one go is a bit irrelevant for the population as a whole.

Yes, but for adults who swim 3km every week (even in one go), it’s only around an hour of low impact exercise

No, but there is a calculation to extrapolate body fat from BMI, as the OP mentions.

My previous post was meant to be in response to this!