BMI - how meaningful is it?

d0nkeyk0ng

BMI was meant for population studies and not individuals. You have someone with a small frame and lots of fat but a normal bmi. Conversely as pointed out above you can have someone who is muscular and lean but with a high bmi.

Gingernutty

The range is for different builds.

Someone with a small frame will go to the lower end and someone with a large frame will go to the higher frame.

For the vast majority of the population, the BMI index is a fairly good indicator.

For athletes and children, it's useless and there are specialist charts for them.

However, the number of people who dismiss BMI calculations, seem to far outweigh the number of athletes and children for whom the BMI calculations are unsuitable.

The stories that one sees in the Daily Mail about apparently normal children being marked as obese, tend to be someone enthusiastically applying BMI charts to children when they should be read off specific chart for children.

I'm short with a small build and obviously obese at BMI of 36. That's correct and I don't argue with that.

We are not all special little snowflakes for whom the normal rules don't apply.

theoretica

Gingernutty wrote: »

The stories that one sees in the Daily Mail about apparently normal children being marked as obese, tend to be someone enthusiastically applying BMI charts to children when they should be read off specific chart for children.

A fair proportion of such stories are about disbelieving parents who don't accept how skinny the obesity boundary is for kids.

jenniewb

OP I wouldn't be too worried about the BMI in terms of a sudden decline in health the second you step outside the "healthy range". I think Theoretica has already explained it quite well; the BMI healthy range was developed as a result of monitoring people's health and illnesses/poor health when in connection to their weight (and BMI).
It was decided the optimal range to be in to be less likely to get certain illnesses such as heart problems, blood pressure issues, certain types of cancer, diabetes and so on. The scientists deciding on the range had used statistics and hit on the BMI 18.5-25 (or there abouts; some variations are 20-25 and no doubt there are others!) It's just as bad to be outside the lower end as it is the upper end.

It's also worth noting that every body is different: the range where my body works optimally is going to be different to the range someone else's body works optimally and although I am not a scientist, I wouldn't be suprized if for some this health range may start inside the healthy BMI range but finish slightly outside of it.


I would also wonder how they obtained the studies for their results; were they based on real people? Were these people living a western lifestyle or did they look into people who are in second and third world countries; I'd wonder if they considered people who are technically overweight AND have a high body fat percentage but are very fit -I know many like this who could easily out run me, an aerobics instructor I had would do about 5 classes every day (in which she took part) and ate a lot -healthy stuff but a lot and was a larger lady. But IMG she had stamina! She had amazing skin and seemed outwardly very healthy but just chose to eat a lot and train a lot.


I'd wonder if they could ever develop a system for those whose lifestyles buck the trend like this. But for most of us, out lifestyles do not go outside the norm: we eat 2 or 3 meals a day, we don't exercise enough or do the minimum with the odd exercise binge a month, we drink too much or don't take on enough water and we are all of similarities when it comes to our physical health (2 arms, 2 legs...etc).


I think the BMI table is a nice generalisation, but that is all it is; a generalisation. If you know you are not the same as the general public; if you know you run 10 miles a day and only ever eat berries and large plates of meat then maybe this table wont apply to you. It is also really just there for a guide. It shouldn't be used as a tool to shake at you and threaten you with ridicule; it is there to say "hey, this table shows that you may be more likely to get this type of cancer or that type of heart condition and as it is preventable I am telling you that if you reduce your weight you will be able to reduce your risk": it isn't there to be a tool to hit you with but a notice of warning to help you help yourself if you choose to.

selement

I'm 4'8. I don't think BMI is accurate for someone oddly proportioned like me, I have particularly short limbs but normalish sized torso (bit on small size). So I think thorax is probably heavier than limbs, so aiming for BMI correct weight would be verging on anorexic.
When I was just over 8 stone was probably a good weight for my height I think. I am overweight now sadly but on slimming world. According to a calculator my ideal weight is 5stone 12lb to 7stone 11lb, but I'm going to aim for 8 stone and be very cautious to attempt to go beyond that! I'm sure most people will agree 5stone 12lb is not a healthy weight for an adult even if they are very short!

FBaby

The range is for different builds.

Indeed, but I agree with OP that when you are especially short, the range seems huge. I definitely know that if I was at the end scale of what is considered normal for my height, I would be fat! The only time my scale hit that number was when I was pregnant!

purpleshoes_2

My bmi is 30.7, putting me into the obese category. Im a size 14, I lift weights, do cardio, over 10000 steps a day and I have a healthy diet.

My number on the BMI scale doesnt reflect my fitness levels and I dont look as heavy as I am on the scales.

My brother who has around 14 per cent body fat and has a slim build and is a pt , his bmi is 25.5 making him overweight.

My body fat percentage and my waist to hip ratio for me are way more important than BMI.

BouncingBean

theoretica wrote: »

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.

What you say makes sense, and I agree with you, except the stuff in bold is actually not true. There are many peer reviewed studies to show that there is not only no direct link between obesity and 'obesity diseases' (correlation does not imply causation). But there was a surprisingly only a very small increase 'obesity diseases' toward the upper end of the 25 to 35 BMI scale. In fact, it's those with BMI's of 23 or lower that was associated with a very increased risk of various diseases. 'Obesity diseases' only started having statistically significant correlations after a BMI of 39 I think it was.

Another interesting statistic, is generally not that many more 'obese' people suffer from 'obesity diseases' than 'normal weight' people. I think there was a few percent in it. But of those 'obese' types that had 'obesity diseases', they had a greater rate of survival than those with low BMI.

There are many peer reviewed, and independent medical papers out there that say a very similar thing - obesity in and of itself is not a health issue. This information has been known for years, but for every legitimate and respected paper, you will find hundreds of sponsored studies and meta analysis's, AKA cherry picking data, to support a conclusion they want supported.

The correlations in legitimate studies that were found, were sedentary lifestyles, and diet to an extent, probably play a more significant role in the controllable aspects of health and well being, as well as other lifestyle factors.

To the OP generally

I personally pay little attention the BMI. What I pay attention to is fitness level - V02 max, muscle fitness. Metabolic health markers like blood pressure and resting heart rate etc, and diet.

Weight alone is a very poor indicator of health and fitness. It's one very small, and often not very significant marker. But sadly far too many people, including some medical professionals pay far too much attention to weight as a health marker.

theoretica

BouncingBean wrote: »

There are many peer reviewed, and independent medical papers out there that say a very similar thing - obesity in and of itself is not a health issue.

There are also studies with huge sample sizes which, without concerning themselves with diseases, note a relationship between BMI and mortality.

http://www.nejm.org/doi/full/10.1056/NEJMoa1000367

And interesting analyses of subgroups, such as this one of people over 65 which finds lowest mortality around a BMI of 24-30, increasing both higher and lower. But, obviously, some people die before 65.

http://ajcn.nutrition.org/content/early/2014/01/22/ajcn.113.068122.full.pdf+html

Of course, as you say, correlation does not imply causation and other factors may have a better correlation to morbidity and what these studies show is that the other factors themselves have a correlation to obesity.

BouncingBean wrote: »

The correlations in legitimate studies that were found, were sedentary lifestyles, and diet to an extent, probably play a more significant role in the controllable aspects of health and well being, as well as other lifestyle factors.

jenniewb

theoretica wrote: »

And interesting analyses of subgroups, such as this one of people over 65 which finds lowest mortality around a BMI of 24-30, increasing both higher and lower. But, obviously, some people die before 65.

http://ajcn.nutrition.org/content/early/2014/01/22/ajcn.113.068122.full.pdf+html

Thanks for this- maybe there's hope for my family yet! :cool: