To think the NHS BMI calculator is dangerous

[Hyggemama]

Posting this as a friend of mine is currently dieting. They've always shown (in my eyes) disordered eating habits, obsessing over what to eat/ not to eat for "health", juice diets, fasting, vegan, carb free etc. They have always been slim and told me proudly now they weigh 53kg. She's 5ft 5in. I was horrified as she's so skinny now, size 6, ribs all showing, but wants to lose more weight for health. She has told me about studies suggesting the lowest BMI in the healthy range is best for avoiding chronic illness. So I checked what would still be "healthy" and according to the BMI tool she could go to 50kg and still consider herself healthy AIBU to think this is dangerous misinformation to spread from the NHS? Also how do I get through to her that skinny does not = healthy? Anyone got any studies to back me up (she loves a bit of scientific research )

Out of curiosity - anyone have a recommendation for measuring body fat %?

The gym scales are rubbish. I've lost 73lbs/33kg, and they record my body fat mass as dropping a mere 18kg, and my fat % dropping a mere 6%.

The lowest BMI weight for me is 7st 2lb. I've been there. As a skeleton with no periods.

I have just give birth, and now weigh 9 and a half stone and I am 5’6”. Not sure what my BMI is but I definitely look healthier now as I was a stone lighter (still in healthy BMI) prior to pregnancy and I looked underweight.

YABVU. The BMI is a useful tool for the vast majority of people to understand what a healthy weight range would be for their height. Athletes and body builders are focused on health and fitness and not likely to use a BMI with no other knowledge/understanding and panic that they’re obese.

Your friend’s disordered eating/beliefs about her size and weight aren’t the fault of the BMI tool!

@14thecatsthecats www.active.com/fitness/calculators/bodyfat

The lowest BMI weight for me is 7st 2lb. I've been there. As a skeleton with no periods

No, the lowest weight for a person of your height is 7 st 2 lb. For a person to be healthy at that weight at your height, they would need a much finer build than what you must have.

I think a lot of the concern over ‘gosh, 18 BMI looks so unhealthy’ is due to living in a society where the majority of people are now overweight or obese. We’re just not as used to seeing people who are very slim and as it looks so different to being fat I think people are unable to acknowledge that just because it’s less common to be slim and at a low healthy weight now doesn’t mean it’s unhealthy in any way.

If she is 8st 4lbs and 5 ft 5 inch, it doesn't sounds as if she is too thin. I don't weigh much more than that and I'm quite a bit taller. I think you are right to be concerned about the fact that she wants to lose more weight though.

Also if you get to the lower end of the "healthy BMI" range the NHS website warn syou to keep an eye on your weight and that there may be an underlying cause or you diet may not be providing another calories. It also suggests you discuss it with your doctor. There is no suggestion that being near the bottom is good for your health.

@Rainbowhairdontcare

Holy crap, that gives me a body fat % of 27 - 12% less than the gym scales!

(which, by the way, before anyone accuses me of being delusional, literally gave me three different weights and BF% within 5m)

It is a good gauge for sizing it is so off as most people are over weight, even a stone here and there. Fitness is vital never mind a gym session, lots of people won't take any exercise they drive to the local school the shop.

It sounds like the suggestion that a BMI of 18.5-20 is optimal is what is dangerous

BMI is a crude but helpful tool used to discuss weight. It's easier to say "your number is X, and this is in X category" than to simply say "you are overweight". Some people see 'obese' as a slur, so having any kind of objective measurement is helpful.

We are made up of more than numbers on a scale, two people could have the same weight and height but totally different fat %s, muscle mass and bone structure. It is dangerous to aim for a lower BMI when this may not be optimal for her frame.

I CBA to google but I'm pretty sure research shows a BMI at the top end of healthy is actually optimum for longevity, 25-26 I think?

Death rate vs BMI is a J-shaped curve.

@Baguetteaboutit 🤣🤣🤣

That body fat calculator seems off to me. It’s about 4% higher than Boditrax or callipers measure me at and even playing with the numbers slightly doesn’t seem to be able to change it much.

I'm 5'5 and weigh 20lbs more than your pal. I'd be mega skinny if I was her weight... But people hold their weight differently so maybe she looks OK...

So I’ve put in a variety of made up weights and measurements and can only get it to say 25 or 26%...

Another article for OP's friend, that J-shaped curve. Study of 3.6 million people. Lowest mortality was when BMI is around 21-25 (among never-smokers, adjusted for a few confounders like diabetes & deprivation).