The fuck is going on with BMI?

[Ottika]

Sure it's altered lately and the NHS calculator doesn't even ask if I am male or female. Why?

I am slim but fit, eat well and balanced, etc etc, and do a lot of heavy hiking, working out for strength, etc. I put some food down!

Myself and DH check our BMI around once per year and it told me that if I lose 2lb I would be underweight. Utter, utter bollocks.

I am a decent size but not at all thin. The BMI calc says that I would be a healthy weight if i gain 2 stone.

Either I am deluded and ill or this is twaddle. I am not remotely skinny and have a few fat rolls when I bend over, even though I keep fit. If I gain a few it feels difficult to tie my boots. I guess I can carry some fat in my gut. But surely as a size 10-12, gaining two fucking stone would be odd?

What is your height and weight?

BMI is, and has always been, a simple calculation: your weight in kilograms, divided by the square of your height in metres. If any place asks for any further information it isn't to calculate your BMI, though it might be used to show you how you compare with others in the same demographic. So you can easily work it out with any calculator. What is called "normal" does vary a bit but usually 20 to 25.

I just checked and you're right. Mine now puts me just into the underweight category, I'm the same weight as before when it had me at 19 so healthy range.

I’ve lost quite a bit of weight recently so have been keeping an eye on this a lot, and yes it seems to have changed slightly. It was 18 for underweight, but is now saying 18.5.

Mine works out pretty much the same as my scales which I have to input on the app that I am female. I’m 5.3 weigh 121lbs and BMI is 21.4. It’s 21.2 on my scales. I’m a size 8 in clothes. Not stick thin just normal and have a few rolls when sat down etc.

Yes you are right. Just checked. It's a bit too generic when not factoring in male or female. Yet they want ethnicity...

If you only have rolls when you bend over, that’s not fat.

BMI is recognised as a measure that overall gives a good indication of healthy weight but not for everyone. A much better indice is body fat % but not everyone can afford a machine that gives you that indicator and most are not much accurate anyway. They are useful to see increases that become concerning.

I'm very small bone and very light bones. BMI is completely inaccurate for me. My BMI will be bang in the middle of normal with fat % that puts me in the overweight category. If I get closer to the overweight but still normal BMI, I move into the obese fat % category.

To achieve a good body fat %, I need to be just under 8 stones, which push me in the underweight BMI. What matters is that I know what is best for my body.

Why would it ask for your gender? BMI is just a mathematical calculation, your gender doesn’t affect the result. They only ask ethnicity because certain diseases are more prevalent at lower BMIs in some races. Their BMI remains the same, but not their health outcomes. That’s not true along gender lines, so isn’t asked.

And yes, you are being ridiculous about your weight. Sounds like you’re very slim and humble bragging about it by pretending you think you’re above average.

If you only have “fat rolls” when you bend over, there’s no way you would “struggle to tie your boots” if you gain a few pounds.

Healthy weight is a spectrum. You’re on the lower end, gaining two stone would put you on the very high end. Nothing weird about that at all.

My bmi is currently 22.5 and I’m about 5 kgs heavier than I am normally (65kgs currently and 171cm). I can be quite fat, it seems, and still have a normal bmi. I do have quite narrow hips and small wrists / ankles etc. so I guess that will skew it a bit. Someone who is bigger built than me would have a higher bmi at the same body fat %. I wouldn’t get too hung up on it. It’s a guide, it’s not useless but it’s not perfect.

BMI was never sex related, it's the same calculation whether you're male or female. If they ever asked for your sex it would have been for statistical purposes (same as ethnicity). It is a bit of a crappy tool, particularly if you're really short or really tall, but as long as you take it with a grain of salt it's fine as a general indicator.

Mine is the same as it is always been around 22 but I am tall so maybe more man size

You must be pretty unfit if you struggle to tie your boots if you put on few pounds. Mobility exercises will help you there and are important as we age.

Bmi is a broad range to account for different body types. It's actually normal and healthy for women to carry some body fat because it's essential for various bodily functions, including hormone regulation, organ protection, and energy storage for potential pregnancies.

If I had a BMI of 18 (ish) I would be a walking skeleton. Thats very very low and not ‘normal’. Why does this bother you? Is it pointing out something others have expressed concern over, that you are indeed underweight and there is an issue?

They did use to have different ranges for males and females. I know because I used to play around with it in the “olden” days.

Bodies are different. It's to allow a range. You're just at the bottom of the range. You know this really. You can see people can be shaped quite differently and still be healthy. We've all seen the Olympics!

You are a healthy weight then? I don’t get the issue. The wide window of healthy allows for different body types.

How can they not care what sex you are? If I was a man I'd be grossly underweight, ridiculously so.

How weird. With ethnicity it's because black people can have more muscle mass in their bodies I think? Also some races are more prone to diabetes etc even in slightly lower weight.

How would you be under weight if you were a man? Men have less fat in general than women.

Don't men have bigger heavier bones and organs, larger hands, feet etc, bigger head on average. A man of my height simply wouldn't weigh what I do unless something was wrong with them I don't think?

Less fat but higher muscle and bone density.

Maybe I just know a lot of skinny men!! Just basing this on a good friend of mine who is 5cms taller than me and a good 10 kilos lighter. He doesn’t look skinny at all. A couple I know are the same weight and she’s a lot taller than him, both look slim.

As @CloverPyramidsaid, it’s a pure mathematical calculation. The healthy range is what can differ, for example, by ethnicity.

I thought the BMI calc's gave percentiles based on sex. Maybe that's only the children's version. But yeah... my adult sons who are much taller are only slightly heavier than me, and my BMI is pretty on target, around 20-21. They have much less fat than I do, are meant to be built like that.

OP, would be good if you gave your height & mass.

It doesn’t ask sex but the calculations are exactly the same for me - I’ve been regularly checking over the last few months as I’m dieting.