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BMI calculation says I am not overweight when my proportion of body fat puts me under the heading of obese.

(43 Posts)
M0nica Wed 27-Apr-22 17:22:19

I am a member of UK Biobank a large-scale research resource, containing in-depth genetic and health information from half a million UK participants.. I expect there are other members on GN.

Recently I was asked to take part in a trial that required me to have all sorts of scans, MRI, bone density etc etc. and yesterday I duly had an interesting time having all sorts of non-invasive tests, including being weighed, body fat assessed etc.

At the end I was given a sheet of paper with some of the results. These informed me that my BMI was, just, in the required approved range. It also told me that 35% of my body was body fat and that means I am also, officially, obese. It seems the approved level of body fat is 25%, which means I am currently a stone overweight.

It has long been known that muscle bound people - athletes and the like, often have BMIs above 25% but as their body fat is low they have no worriess.

What is never mentioned is that, if like me, you have a narrow and slight frame, you can be lulled into a sense of false security in thinking that as your BMI falls in the approved range so you can be sure you are at a healthy weight, yet you may actually be, not just overweight, but obese and need to lose weight to protect your health.

I have suspected this for sometime, I can see the rolls of fat. Also about 30 years ago during a Healthy Life event at work, long before the BMI was used, my body fat was measured roughly with callipers and I was told then that I needed to lose about half a stone.

But it is only yesterday that I finally got figures in writing that prove, quite conclusively, that I fell within the approved BMI for my heigh but that actually, because of the amount of body fat I have, I am also classified as obese - not overweight or the other names used to classify those mildly overweight, but obese.

I am left wondering how many other people there are in country are reassured that their BMI means that their risk of strokes, heart attacks etc is minimised when they are actually anything from overweight to obese and at higher risk of those maladies.

Who and why did anyone ever think that the BMI was a reliable statistic to assess peoples weight and whether it was healthy or not?

Anyway the diet started today and I am determined to lose that extra stone, now I know quite conclusively that I am obeset, whatever BMI and my dress size says.

Kate1949 Wed 27-Apr-22 17:38:33

Interesting. Thank you. I've long suspected this to be the case. My BMI is currently 22.5 and tells me I am a healthy weight and that I should continue to do what I'm doing. However, I too have rolls of fat around my middle and need lose a bit of weight.

silverlining48 Wed 27-Apr-22 18:03:38

How interesting to be able to have all those tests Monica and find out so much.
I am far too short for my weight and have battled to grow taller ( probably need to gain at least 10") but so far had no success.
Seriously though i think you and kate too with BMi of 22 really don't need to worry too much. As we age our skin gets looser and if i dare say flabbier, Mine feels like jelly. Do check if this is necessary.

Kate1949 Wed 27-Apr-22 18:12:28

It's strange silverlining . My husband has never been overweight. He has always been slim with not an ounce of fat on him. He is the same weight now as when we married 52 years ago. However, he now has a fat tummy. He exercises regularly. Things just change as we age, despite our best efforts I suppose.

Jane43 Wed 27-Apr-22 18:33:36

I think the BMI index is outdated as others have pointed out because it doesn’t differentiate between fat and muscle. I think there are scales that measure body fat and these may be more useful than the traditional scales. A more recent measure focuses on the waist and the guideline is your waist should measure no more than half your height. Kate1949 it is inevitable that we lose muscle mass as we age and although your husband’s weight has remained stable it probably consists of more fat and less muscle than it did 52 years ago.

Jane43 Wed 27-Apr-22 18:39:57

Something else I should have mentioned is that even people who appear to have little fat often have internal fat, termed visceral fat around their abdominal organs and this can be very dangerous. It was featured on a tv programme featuring Angela Rippon and Doctor Michael Mosley. Angela appeared to have little body fat and is very active still playing tennis regularly but when measured she had a high level of visceral fat. I believe it is hard to measure visceral fat.

Kate1949 Wed 27-Apr-22 18:42:12

Yes I've heard that Jane.

Whitewavemark2 Wed 27-Apr-22 18:45:54

Mum died at 101, and until the last 18 months had good health although frail.

She was always active, but at 5’3” she was a size 18 - so pleasingly plump.

Almost certainly obese all her latter years doesn’t seem to have made any difference at all.

V3ra Wed 27-Apr-22 18:55:07


It's strange silverlining . My husband has never been overweight. He has always been slim with not an ounce of fat on him. He is the same weight now as when we married 52 years ago. However, he now has a fat tummy. He exercises regularly. Things just change as we age, despite our best efforts I suppose.

Has he lost height at all?
My Mum had osteoporosis and as she lost height through this her tummy stuck out more and more, which really annoyed her!

silverlining48 Wed 27-Apr-22 18:55:19

Like you Kate we have been married 52 years and though my dh weighs a little more than then, he still almost fits his Take 6 carnaby st coat, bought in 1966 and keeps trim. If I moved the buttons an inch the coat wouid fit. Its a great coat.
We eat the same, but I am always more careful than him, always have been, we both walk with a group and on our own, his other hobby is sedentary, yet its me with the problem. Quite a big problem, if only i was taller.

silverlining48 Wed 27-Apr-22 18:59:01

Oh i did mean to mention the dh has one too thats why i need to move the buttons grin

silverlining48 Wed 27-Apr-22 19:04:40

Jane is right the bmi rules were arbitrary, but the half waist to height measurenent means i shoukd have a 30" waist, I wish. ! I cant win, sad

CanadianGran Wed 27-Apr-22 19:11:59

I tend to think BMI is a very rough calculation. I clock in as a healthy weight, but I know I have a middle aged roll and could stand to lose 10lb.

It tends not to take into consideration frame size, and muscle density. Someone my weight and height could be very sturdy and muscular, or light framed and carrying body fat.

There is a measurement for body fat using measurements of neck, waist, hips that paints a better picture because it takes into consideration your weight distribution.

TillyTrotter Wed 27-Apr-22 19:18:08

I was once told I had perfect a BMI measurement by a nurse. (about 5 years ago).
I weighed only 8 stones 4 pounds and everyone said I looked gaunt, old and ill.
Since then I have put another stone on and look much better.
I doubt a nurse would say my BMI was perfect now.
I don’t set a lot of store by it.

silverlining48 Wed 27-Apr-22 19:22:27

Losing midrif flab is very hard post menopause, The trouble with losing weight especially if not really overweight is it usually goes from the face first and people start to look very gaunt.

LtEve Wed 27-Apr-22 19:22:50

I know that you can be 'slim on the outside, fat on the inside' which can be a problem for health. We are seeing a lot of men in their 30s who exercise and are slim but are having heart attacks, it turns out they have high levels of plaque in their coronary arteries totally unknown to them. This seems to correlate with the adage 'you can't outrun a bad diet'.

silverlining48 Wed 27-Apr-22 19:22:57

X post Tilly

MerylStreep Wed 27-Apr-22 19:33:45

The height / weight thing has cheered me. I’m 5’ my waistline is 32 1/2 . I’ll take that 😊

silverlining48 Wed 27-Apr-22 19:41:09

I am 5 ' ( and a very important half )too Meryl and would also be very happy with that.

M0nica Wed 27-Apr-22 19:43:38

silverlining, sadly there is no way out. I was measured in a machine that specifically measured my body fat and my muscle content. 35% of me is fat and it should be 25% and in my case that means I need to lose 14 lbs.

jane43 BMI was never a suitable statistic to use in the first place. It is an economic statistic, devised to do something completely different and only to be applied to groups of people not individuals.

It is making the same mistake Gavin Williamson did with A levels in 2020. Assuming because a schools previous results in A levels in any given subject was 25% As, 50% B 20% 10% Es that each child should get a mark based on this group result the following year, even though the next year more children might have achieved a higher standard and fewer a lower one, or vice versa

silverlining48 Wed 27-Apr-22 20:00:41

Monica wishing you well. Its been a lifetime struggle for me, but I battle on. Good luck.

BlueBelle Wed 27-Apr-22 20:01:31

I have no interest in measuring anything 😂 I am exactly what I am neither fat nor thin I cannot be huffed to keep worrying about losing pounds at 77 I d look gaunt and drawn if I started losing the half stone I probably would be told needs to go because it never goes of the areas you want it to go off it wouldn’t go off my waist or tum it would go off my face or my arms or legs which are already slim

Kate1949 Wed 27-Apr-22 20:28:32

No he hadn't lost height V3ra

grannyrebel7 Wed 27-Apr-22 20:40:07

Interesting MOnica. Just wondering how you get involved in these research things. I would love to do it.

silverlining48 Wed 27-Apr-22 21:07:20

Think it might be random. We have been approached and been asked to do 3 dfferent studies, the oldest began nearly 40 years ago. We do that one once a year. The otger two are since covid,
I never win raffles but we are clearly random type people.