NHS bmi

That’s why BMI is such a poor metric, it doesn’t take any of that into account!

I don't think the thresholds are different though? Over 25 is overweight, over 30 is obese, for both men and women.

The calculation is the same, but shouldn't the thresholds be different? A slim woman of the same height as a slim man would probably weigh less than him, as men generally have a greater muscle to fat ratio than women do, and muscle weighs more than fat. So the BMI value which gave 'healthy' for him, could be 'overweight' for her, and 'healthy' for her could be 'underweight' for him.

At least, that's how I have always understood it, and why they asked for your sex.

Breasts don't weight much. BMI is a useful metric, as body fat, which is the only true way to tell, is hard to measure accurately without certain equipment. BMI actually tends to overestimate the number of healthy people because many within the healthy range actually have too high body fat.

As far as I remember from playing with it before it changed, the number was the same but the accompanying advice given varied depending on sex. The same as it does with ethnicity.

@MarthaMayWho Race isn't there, it would be ridiculous if it were but there are options to select ethnic background.

I've just checked the app, and the advice had also changed - whereas it previously warned that I was at the bottom end of the healthy weight range and I should avoid losing weight, it now just tells me I'm a healthy weight.
Seems to me that these changes are a tacit acknowledgement that it's all a bit meaningless, and they are moving away from making personalised recommendations based on the number that the algorithm churns out.

I looked at that a few days ago because DH has lost weight and I am convinced he is underweight. Yet it has him in a healthy weight category 🤷‍♀️

I hope actual doctors don't take any notice of that.

I work for a company that does a lot of back-end work for health providers - including things like building tools such as the BMI calculator.

The teams actively involved in these things aren’t men only - there’s a lot of women now from coding right through to testing and implementation.
It’s a bit silly to say it doesn’t matter because you’re a woman, especially when BMI is a single measure for both men and women.

I agree... but I've also experimented with saying I was male, and it made no difference either to my BMI (which of course it shouldn't, as the calculation is exactly the same) or the advice given as a result of the calculation. Given this, and the fact that BMI is a pretty blunt instrument, I think it makes sense to stop asking for sex.

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.

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.

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.

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.

@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.

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.

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?

Sex is medically significant no matter what age you are.

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

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.

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!)