BMI - how meaningful is it?

elsien

Just put my details into a BMI calculator, mainly out of curiosity.
And for my age and height of 5 ft 1 it gives a healthy weight as anything between 6 st 14 and 9 st 7.
Now I know there's a bit of individual difference, and I've always tended towards the lower end of the scale. I eat normally, it's just how I am.
But a two and a half stone difference for someone comparatively small seems like a huge difference to me. So out of interest is there any debate on what is a healthy BMI and how accurate a measure it is?

System

I believe the BMI chart is unisex. That could account for the weight range, as men tend to be heavier than women.

http://www.nhs.uk/Livewell/healthy-living/Pages/height-weight-chart.aspx

elsien

No, this one asked if you were male or female before doing the calculation, so I presume that was factored in.

theoretica

BMI is often taken to be more than it is. Change from 9 st 7 to 9st 8 and you won't suddenly, and personally, fall off a health cliff - for you that pound isn't any more important than any other. What is important is the statistics of a lot of people - if you took 1000 people with a BMI of 35 they are likely to have or develop more of certain health problems between then than 1000 people with a BMI of 25. But you would find healthy people in the heavier group, and health problems in the lighter people too.

Apparently an experienced person looking at you can be better at deciding if you personally are a healthy weight than the general calculator. But this is harder to do at home, and some people would really not like being told that they look too fat or thin, even by a medical professional, and might accept the scales more easily.

cherryblossomzel

elsien wrote: »

No, this one asked if you were male or female before doing the calculation, so I presume that was factored in.

BMI is calculated only on height and weight only. Sex and age is irrelevant.

As theoretica said, it's a good tool for populations, less useful for individuals. But it's a very easy measurement, both height and weight is easy to measure. It's much more difficult to measure other factors, like muscle mass or fat mass, or bone density. It's a quick and easy tool for medical professionals.

There're a couple of interesting sites showing how different people's bodies are, even at the same height and weight.

https://www.flickr.com/photos/77367764@N00/sets/72157602199008819/

http://www.mybodygallery.com/search.html?height=5

http://www.cockeyed.com/photos/bodies/heightweight.html

I seem to recall reading that BMI is useless for anyone either very short or very tall. It's definitely useless for anyone very muscled.

scooby088

Bmi is meaningless really i think my bmi is in the higher 20's, i know i am atleast 6 stobe overweight, yet a friend whose a bodybuilder has about 4% body fat is around the same bmi, that example may not be scientific but shows bmi is pointless

WantToBeSE

I believe that the BMI is outdated.
I would say that as long as you don't look overweight, eat healthily and get enough exercise, you are OK.

nonnatus

It's a ridiculous system.

My lovely son is applying to the Air Force and for his age group, they have an upper limit BMI of 27. He is 5ft 11, with the physique of a rugby player (because rugby is his passion). His actual BMI is 27 and he's panicking now, avoiding eating lunch etc. It drives me mad - he's a healthy teenager, certainly you wouldn't look at him and say "he's fat / overweight / obese".....

SailorSam

For a healthy Bmi i could do with losing about 3lb. So i'm more or less happy as i am.

belfastgirl23

I think BMI is a useful guideline, especially for less active people. It's a general rule of thumb in terms of weight management. But it needs to be used with a degree of flexibility, as nonnatus says having a BMI of 27 if you're a 27 year old rugby player is a lot different than having a BMI of 27 if your main focus in life is online gaming and eating crisps on the sofa


I'm always on the high end because I carry relatively a high amount of muscle. Which unfortunately at the minute is topped off with a lovely thick layer of fat But my goal BMI is around 25/26, I know this is healthy and sustainable for me.

InsideInsurance

Its a basic tool that is easy to measure with nothing more than a tape measure and scales.

Whilst BMI score is independent of age/ gender etc some guidelines do adjust the targets based on these factors.

As others have said, as a crude tool you should take it with a pinch of salt and there are much more exact measures that can be done but typically require more equipment. There are also known things that will skew the results but arent things to worry about (ie being highly muscular)

To the OPs original question about there being a 2.5 st band for "normal", the reality is that life isnt black and white but shades of grey and so there is more transition from "normal" to "overweight" to "obese" than the scale allows for but having "almost overweight" and "a bit overweight" etc to further divide the scale just adds unnecessary complexity when its an acknowledged crude tool.