NHS bmi

[MarthaMayWho]

I was well versed on the NHS Bmi. You used to have to put in male or female and your ethnicity. Changing the sex used to massively skew whether you were in the health zone or not.

NHS bmi tool now has no option to choose sex so now a blanket bmi.

Surely this is going to cause problems?

BMI is a nonsense metric anyway, I'm surprised the NHS is still using it. Women in particular have a huge range of body shapes and composition due to breasts and hips

(https://www.medicalnewstoday.com/articles/265215#Waist-size-linked-to-diabetes-risk,-regardless-of-BMI)

As the link says, waist size is a much better guide to people's health risks than a metric designed by a 19th century Belgian mathematician who was literally trying to find out the "average man" - not invent a health measure.

I like bmi. Like you say, women have a natural range of sizes and my natural waist is huge (even when I was underweight and had an eating disorder I registered as 'fat' according to waist measurements.
Bmi worked for me, gave me an achievable goal when I had to lose baby weight as it would subtly change with each kg. Waist size doesn't do that.

Just because it is not accurate for some people doesn't mean it's ok to make it less accurate for women.

I swear that the healthy range for my own height has been changed by this! It used to be a kilogram higher!

It’s based on one chart so I don’t see how it makes a difference?

Just checked this out and on the NHS calculator I am now 1.1 BMI points higher than on a health app which uses sex. NHS asks ethnicity but not sex.

My BMI is unchanged as expected but I don't like that they've changed it. I tried clicking on the survey option but it's not available

This seems a bit confused. BMI is defined, and always has been, as the person's mass in kilograms divided by the square of their height in metres. If anywhere is giving a number that is different for people of different sexes/ethnicities/gender/eye colours, then whatever that number is, it isn't BMI. It could be that different sites use different cut-offs for what they consider healthy, based on those things, though - is that what you mean, OP? What's the page you're looking at? The easily found NHS BMI calculator seems to be this one, which I don't think has changed much in a long time. It doesn't ask for sex (or gender) but I don't think it ever did.

www.nhs.uk/health-assessment-tools/calculate-your-body-mass-index/calculate-bmi-for-adults

It's changed, and very recently I'd say. I check my BMI using this tool and last did so a couple of weeks ago. It has ALWAYS asked for sex and provided a clickable link to 'why do we ask this' information for the question.

Bingo!
Page last reviewed: 28 November 2023

I don't see why it matters? It's the same calculation for men and women isn't it?

BMI calculators definitely used to commonly ask for sex to be able to tell you whether the BMI is in the normal range or obese etc (which sex is often relevant to). The NHS calculator still does ask for young children and teenagers.

A child or teenager's BMI is shown as a "centile". The centile result is shown as a percentage of how their BMI compares with other children or teenagers of the same age and sex.

Sex

Please enter sex
Why are we asking?
For children and teenagers, BMI centile is sex specific. We give more personalised information based on whether you are male or female.

https://www.nhs.uk/health-assessment-tools/calculate-your-body-mass-index/calculate-bmi-for-children-teenagers/

Yes, and nothing about the thresholds (underweight below 18.5, normal 18.5-25, overweight 25-30, obese over 30) has changed from what I'm used to seeing either (I only checked for white ethnicity - there's an argument for Asian ethnicities having different thresholds but I don't know details and wouldn't know if that has changed). Maybe (if they've really changed the calculator) the new thing is that they used to ask for sex and then do nothing with it, and now they don't ask? I have no explanation for the people above who say their actual results have changed though.

Yes - that's because BMI is defined differently for under 18s. But for adults it's the same calculation isn't it?

Ah, no. BMI is not defined differently for children, but BMI centile depends on the population it's being compared with, and that's what you do with children. Eg (made up example) maybe a 14yo girl with BMI 18 has higher BMI than 55% of 14yo girls and lower BMI than the other 45% of 14yo girls. Her BMI centile is 55, and that's a more useful number than her actual BMI. (Still not all that useful, but that's another story!)

I'm not saying the calculation has changed. I thought my post was perfectly clear that the reason they used to ask for sex was about thresholds for underweight, healthy weight and obesity, as for children, and it's the same reason why some calculators ask about ethnicity.

There is only one way to calculate BMI, honestly - that's both the strength and the weakness of it as a measure!

Sex is medically significant no matter what age you are.

Fenlandia made a good point.
BMI is good for population level studies of weight, not really helpful for an indvidual. I thought there was a switch to waist hip ratio these days?

Do you remember anything about what the threshold differences were? As I mentioned, the ones given now are definitely the familiar ones to me as a (white) woman, and I am pretty sure the same thresholds used to apply to men too, just as they do in a unisex calculator.

Come to think of it, here's a possibility that might make sense, though it's made up on my part: it could be that when they first recognised that the thresholds they were using made no sense for Asian women, they changed them only for Asian women, leaving Asian men with the same thresholds as white women and men. Then investigated more and decided ethnicity was the factor that mattered and sex shouldn't be used there either, and removed it from the whole calculator. That's just me imagining though.

No argument, by the way, about sex mattering at every age in medicine! It doesn't, however, have to be a factor in every crude rule of thumb or threshold.

@Ereshkigalangcleg but I don't think the thresholds are different either are they? Above 25 is overweight, above 30 is obese, for men and women.

I definitely remember the calculator asking for sex, whether they factored it in or not. I haven't checked it in a while so I don't know how long ago I'm referring to.

But the thresholds for adults are the same regardless of if you’re a man or woman. If you look up a BMI chart it’s easier to see how it works.

The NHS calculator definitely did ask for sex.

Its strange to me that they calculate ranges for race but not sex? Im about the same height as my husband, and if we were the same weight, I'd definitely be a lot fatter than him.

There are ideal weight charts and they give different target weights for men and women based on height. But i dont know how they came to the ideals.

Fenlandias point totally disregarded those of us who use bmi as a running tracker whilst losing weight as I explained above.

If you look on the coloured tracker I am now a great deal 'healthier' than I was last week as a visual tool. I'm not. I've lost nothing this week.

Regardless of what's best for the population blah blah, as a visual tool it now makes me look far more into the healthy weight section than previously, yet I'm still fat.

I used it before and it worked really well for me. As I said, yes maybe it doesn't work for everyone but I find it much less demoralising than waist measurements and much easier to see progress.

It's become less accurate than previously for those of us who used it this way and that's not ok. I'm not really interested in whether or not waist measurements is the most recent trend or whatever, as my body shows, not every method works for everybody.

I mean, great as an ego boost but if I stopped slimming now I'd do my long-term health damage. But I suppose that doesn't matter because I am a woman eh, and the little tweaks only effect women.

If it works for you OP then more power to your elbow! I find weight management very challenging so I salute anyone who is making progress towards their goals.

I share your annoyance that sex seems to have been removed as a criterion for BMI. Women have more body fat on the whole than men so it is not helpful to measure us against the literal average.

But excessive weight around the waist is correlated with many poor health outcomes such as high cholesterol and diabetes so it seems useful to me have that as a tool too, even if it is 'demoralising' to have to think about it.