BMI - All Its Cracked Up To Be?

[PawPaw]

- BMI was always intended as a research tool for interpreting populations, not small samples such as N=1.
- the reason it is inappropriate as an individual guide to overweight is because humans can be healthy outside of the healthy ranges. Asians and Polynesians have different healthy BMI ranges to Caucasians, lean tissue can be developed in someone with sub 15% body fat above healthy healthy BMI range.
- a primary contact health professional, who knows what they are doing, doesn't use BMI. BMI seems to be something people who work outside of health and read a lot of websites, get hung up on. Though admittedly, many primary health pros are not as objective or skill in communication, as their job requires.
- the reason some health pros bandy around BMI as a guide for individuals, is that it is only a very small % of the population that develops lean tissue to the extent they have a BMI outside normal range and simultaneous healthy bodyfat%.
- It also should be understood what "healthy" BMI range indicates. It doesn't mean you will have optimal health in that range. It means outside that range, you are more likely to have a higher statistical probability of developing prevalent morbidities. Some of these morbidities may not manifest for 20-40 years. This should put into context anecdotal reports about people's experience over 1-5 years.

- So BMI is not all that it is cracked up to be, by those who don't understand its limitations. If you are seeing a health pro about a weight issue, and they are guiding you with BMI, drop them, and find a health pro who uses and is competent in skinfold testing, or imaging techniques.

- if you want to understand what is and isn't healthy body fat percentage, or what is optimal for a specific sport, read up about that specifically.

- finally, understand that medical consensus re advice on this matter is heavily influenced by cultural factors. Two examples:
1. As you age, GPs in general advise carrying additional body fat is preferable, as it provides additional energy during chronic illness. However, there's no evidence older slimmer Asians have more health complications. And in fact, it's possible carrying additional fat increases the risk of getting sick more often. From my conversations with many doctors and researchers in the field, doctors are more concerned older people get adequate nutrition. Living alone, depression, presenile dementia, dehydration, and malabsorption issues, can cause malnourishment, and it's these factors more likely driving GP advice for older people to carry more fat.
2. GPs regularly see the problems of people aiming for lower bodyfat and not attaining it for the long term. They make a decision the lesser of two evils is to carry additional bodyfat. That decision might be best in the short to medium term interests of the patient, but not the long term. Interestingly, these problems are not prevalent in traditional Asian cultures. They seem a problem primarily of Western style affluence.

[ColinOldnCranky]

A recent British study I have heard about but can't find at this stage discounts BMI in favour of waist to height ratio as a better health indicator, anybody have more luck finding specifics?

I have not heard of it myself. Try googling for the study with hip-to-waist-ratio instead. This seems to have found broad favour in place of BMI in recent times. It is supposed to give due weight to the effect of WHERE the fat is located rather than quantity. More around the middle is worse, reducing the efficiency of the heart and lungs. Or smething like that in my understanding.

[ColinOldnCranky]

As you age, GPs in general advise carrying additional body fat is preferable, as it provides additional energy during chronic illness. However, there's no evidence older slimmer Asians have more health complications. And in fact, it's possible carrying additional fat increases the risk of getting sick more often.

Huh? Yeah, maybe for an old person who has lost so much body mass that they are now skinny, and a lot of the elderley do thin excessively. Bu they would be s-k-i-n-n-y skinny inthe extreme.

If you can find anything that supports, for example, a person of ANY age and in a decent weight range (ie not chronically skinny already) being advised to add weight then I would be VERY interested to see it. Seriously. It would be worth looking into. I have never heard a doctor telling a person of any age(and I have had an excessivley large number of elderley in my family for which my wife and I have had some responsbility in old age, all now deceased) with an already healthy weight (say BMI between the conventional 20 to 25) being advised to add a few pounds. Rather the advice is commonly along the lines of diet control to address type II diabetes. Or to put on weight as they skin and bones and are well below the norms.

Perhaps someone who works for an retirement home may have some comment on this.

[PawPaw]

A recent British study I have heard about but can't find at this stage discounts BMI in favour of waist to height ratio as a better health indicator, anybody have more luck finding specifics?

From memory, the latest is, as a guide, waist circumference is better than BMI, waist/height ratio, and waist hip ratio.
However, when they make statements like 'guide', it is statistically determined. If 10 in 1,000 people are body builders or muscular athletes, with low body fat, that guide will be determined to have a statistical error <0.01, which scientists consider a reliable measure. The fact that it is totally wrong for 10 people is glossed over. However, some time ago, I noted AUstralian health resources on the net were getting better with their footnotes in relation to sub populations that BMI will be misleading.

[PawPaw]

Perhaps someone who works for an retirement home may have some comment on this.

That would be me.
Well I've contracted to 3 retirement homes, worked in 8 hospitals, had working relationships with dozens of GP friends through the years, had a GP partner, and had many clients tell me they don't want to lose weight to help their arthritic knees, because their GP told them carrying a little extra fat is insurance in later years (this included my mother), and that their current weight is fine.

Maybe your family's personal experience with 1 or 2 doctors has been different.

[ColinOldnCranky]

A recent British study I have heard about but can't find at this stage discounts BMI in favour of waist to height ratio as a better health indicator, anybody have more luck finding specifics?

Found something jsut reported in teh literature (and therefore will be subject to further research and confirmation or otherwise. Look at http://www.dailymail.co.uk/news/article-2143709/How-eating-English-breakfast-hit-waistline-just-hours.html and the paragraph

The finding comes in the wake of a warning that fat which settles around the middle is particularly harmful and could take years off your life. The European Congress on Obesity heard last week that the secret of a long and healthy life is as simple as keeping your waist circumference measurement to under half that of your height.

Read more: http://www.dailymail.co.uk/news/article ... z1unqnFwki

Interesting.

[ColinOldnCranky]

Perhaps someone who works for an retirement home may have some comment on this.

That would be me.
Well I've contracted to 3 retirement homes, worked in 8 hospitals, had working relationships with dozens of GP friends through the years, had a GP partner, and had many clients tell me they don't want to lose weight to help their arthritic knees, because their GP told them carrying a little extra fat is insurance in later years (this included my mother), and that their current weight is fine.

Maybe your family's personal experience with 1 or 2 doctors has been different.

That's fine. It just didn't gel with my own experience and piqued my interest. I fall into the not-so-young-anymore category so I'll maybe have a chat with my own GP next time I see him.

[PawPaw]

From http://en.wikipedia.org/wiki/Waist%E2%80%93hip_ratio

"If obesity is redefined using WHR instead of BMI, the proportion of people categorized as at risk of heart attack worldwide increases threefold.[10] The body fat percentage is considered to be an even more accurate measure of relative weight. Of these three measurements, only the waist–hip ratio takes account of the differences in body structure. Hence, it is possible for two women to have vastly different body mass indices but the same waist–hip ratio, or to have the same body mass index but vastly different waist–hip ratios."

(WHR= waist hip ratio)

[twizzle]

I just loved that bit on that Jamie Oliver special where they did full body scans of the participants and in a couple of cases the skinny people had more fat around their organs and as a percentage of body weight that the fat-looking-but-strong tradie. Looks and measurements can be deceptive.

[Mulger bill]

Try this one - contains links to actual research papers

http://en.wikipedia.org/wiki/Waist-to-height_ratio

This link gives you a calculator

http://www.shapefit.com/calculators/waist-to-height-ratio-calculator.html

Thanks Hamster, I'll wade into them when I have a bit more time, say about 0130 tomorrow.

Shaun

[Comedian]

Whilst this thread has got somewhat side tracked from my original intent, and turned into an examination of my individual case which was absolutely not the intent, the case is:

Weight = 115 kg
B F = 23% - depending on accuracy of measurement maybe 3% less
Muscle mass = 88.55 kg
BMI Maximum Target weight = 85 kg

Therefore how can BMI be accurately reflecting my individual case. This was the point i started with. This is the point I keep making. If my muscle mass is more than my BMI target weight how could it possibly be accurate? If as I loose weight I increase muscle mass (as has been happening) then it is impossible for me to achieve this target. My point is one of wondering how many other people are in this model? Or more to the point how many people should be but are being 'educated' to a weight target that is not realistic for them?

I'm sorry again.. in a "normal" individual around 57% of your body mass is water. You aren't 88.55kg of muscle and bone I'm afraid...

[dynamictiger]

[quote="ComedianI'm sorry again.. in a "normal" individual around 57% of your body mass is water. You aren't 88.55kg of muscle and bone I'm afraid...[/quote]

Comedian I use this term as it is what the nutritionist call it I attend. Whether the balance is water, bone or muscle adn exact composition is not the focus. Nor is the focus my individual case. It is more about the fact my target weight according to BMI is in all likelihood unattainable in the normal sense of the word. Therefore I am questioning whether BMI is an appropriate tool and if it isn't what is and so on?

[vander]

WHR is the way people are going now it is a lot more specific to health related issues, in fact it is better than calipers because a lot of people can have lots of sub cutaneous fat but not much visceral or vice versa this can account for, some, of this. Imaging is the gold standard but too expensive/difficult and not worth it when WHR and calipers give a good enough idea for most people.

@DT: I think it should of been fat and fat-free mass not fat and muscle which is the way it is commonly done.
@Comedian there is water mass in fat molecules also so that can be deceptive.

[wombatK]

Whilst this thread has got somewhat side tracked from my original intent, and turned into an examination of my individual case which was absolutely not the intent, the case is:

Weight = 115 kg
B F = 23% - depending on accuracy of measurement maybe 3% less
Muscle mass = 88.55 kg
BMI Maximum Target weight = 85 kg

Therefore how can BMI be accurately reflecting my individual case. This was the point i started with.
This is the point I keep making. If my muscle mass is more than my BMI target weight how could it
possibly be accurate?

The point you started with was that BMI is not all that it is cracked up to be (the thread title). Then
you launched into this paragraph:

I will kick it off by stating I do not agree with BMI. I think it is absolutely nonsense in my specific case

If you don't want it to turn into an examination of your individual case, then don't start with
paragraphs like that. And don't redraw focus on your case as you do in the paragraph
immediately above. Right next to your complaint about focus on your case, you are once
again citing your case as evidence BMI isn't accurate. If that's not nonsense, nothing is.

Your criticism of BMI might be better served by focusing on more than a trivial percentage of
the population and showing that they have been incorrectly identified as obese by BMI measurement.

When you let the focus drift from individuals and take in the vast majority of the population,
the World Health Organisation and the USA's National Institute of Health accept it is useful in
identifying obese people. There is such a low percentage of people that aren't accurately identified
by it that it isn't worth the expense of adopting other methods.

And while other low-cost methods like WHR are gaining support, the evidence base is not sufficient to
supplant the current WHO/NIH recommendations.

You might be surprised to learn that most GP's and dietitians are very good at estimating people's
weight, nutritional status, and whether or not they are obese without any measurement - other
than their trained eyes picking out salient tell-tale anatomical features. It would be a very poor
doctor that was relying on a BMI measurement alone to classify a patient as obese or over-weight.

But if you really believe you are in that small percentage of people that these measures don't
apply to, and that the GP who told you were overweight was incompetent and used no other
clues, then go to the expense of using other methods like under-water weighing or DXA scanning.

Otherwise, you'll never really know whether BMI is not all it's cracked up to be - you're just guessing
at best, and at worst, denying. And that's nothing anyone else can put much faith in.

[twizzle]

So, given that on the other thread people just launched and said that denying your individual BMI was heresy, now we have the opposite where DT is being pilloried for applying it to the individual. Cake and eat it too?

BMI is about as relevant as the 'max heart rate' formula - it's useless at the individual level, so why do people bother calculating it for themselves?

[simonn]

BMI is... ...useless at the individual level, so why do people bother calculating it for themselves?

The BMI can act as an easy to measure and calculate guide for the statistically average healthy weight for your height. If you are not or do not consider yourself to be average in this context there are more accurate, but harder to measure/calculate, methods which can also be used.

It is not useless, people just put to much weighting (pun intended) on it.

[ColinOldnCranky]

From http://en.wikipedia.org/wiki/Waist%E2%80%93hip_ratio

"If obesity is redefined using WHR instead of BMI, the proportion of people categorized as at risk of heart attack worldwide increases threefold.[10] The body fat percentage is considered to be an even more accurate measure of relative weight. Of these three measurements, only the waist–hip ratio takes account of the differences in body structure. Hence, it is possible for two women to have vastly different body mass indices but the same waist–hip ratio, or to have the same body mass index but vastly different waist–hip ratios."

(WHR= waist hip ratio)

I don't it as redefining obesity and, without reviewing the article, I saw no reference to it doing so. Rather just claiming a better indicator of it's health effects.

Which is nothing new - for a long time now we have been informed that excess fat around the middle for instance is worse for certain health outcomes than excess fat elsewhere. So you could just as obese as another person but with a different distribution it may be a lesser or greater problem than the other persons. Though the problem will still be there for both.

[dynamictiger]

[quote=”wombatK”]If you don't want it to turn into an examination of your individual case, then don't start with
paragraphs like that. And don't redraw focus on your case as you do in the paragraph
immediately above. Right next to your complaint about focus on your case, you are once
again citing your case as evidence BMI isn't accurate. If that's not nonsense, nothing is.[/quote]

I think there is confusion here, unintended. Yes I use specific example, my case, as it is my opnion there are many people like me. Contrary to what statistics may say.
I come into contact with hundreds of people throughout the year and whilst I am not exactly a tiny person, I am not overweight compared to others of similar dimensions. In fact I would venture a guess I would be perhaps 40-50 kgs lighter than many of these other chaps I know. Now I am not saying I or they are in perfect shape. What I am saying is from this sample group of chaps over 1.85m tall and over 130 cm in the chest I doubt any of us would comfortably fit the BMI models.
Further I understand from my own research, which was generated out of curiousity i.e. why don’t I seem to fit this model, the country of origin, the sample groups etc were so far removed from both my background and my ancestry I wondered how many others may be in a similar position. Hence the title is BMI all it is cracked up to be?
I am not a pacific islander or asian. I would be considered a Caucasian male. Yet from the research and math models it is quite clear not once in my lifetime have I fitted into the BMI scale. Not that I have gained or lost significant weight or height. Rather the BMI scale simply does not apply and in fact you would have to consider laughable if you were to meet me. At my fittest point at age 17 I weighed in at 110kgs. Yet BMI scale states I should be 85 kg maximum. Clearly there is an error in my case. Yet the proponents of BMI would have us believe it applies to all Caucasian males and anyone that does not fit this model is overweight. Really? At 110kg I carry a very healthy six pack. As has been mentioned previously for this to occur the body fat percentage has to be about 10%. So again using what I know. This suggests there is an error in the BMI that needs to be considered.
I am not saying this applies to all the population.
I am not saying this is the final word on BMI
I am saying there are some people, who are so far removed from the average that they fall well outside the BMI targets.
As mentioned elsewhere I am not your average cyclist either. I am not here for racing, touring or anything like that. I happen to enjoy using my bike as an adjunct to other exercises I do and as a means of transport on some trips I do.
[quote=”wombatK”]There is such a low percentage of people that aren't accurately identified
by it that it isn't worth the expense of adopting other methods.[/quote]
I am also questioning this as well. No doubt someone will roll out statistics to prove I am wrong, however my simple observations are different population groups seem to exhibit different characteristics.
What I mean is, and again I need to resort to personal examples, in NZ I am very tall, very broad and very seldom do I come across many people taller than me. At times I do, however it is unusual. In Western Australia, without trying I can think of at least 9 people I know who are taller and 5 who are broader than me.
Anecdotally this would suggest there is a different gene pool active in WA. The outcome may be a different model needs to be considered. Or perhaps an alternative BMI needs to be considered where other body dimensions other than height are considered.
Again the intent was not personal, although of course personal experience is what everyone knows best. The intent was to see what others thought and how many others may be in this group of people that do not fit this model readily.

[rkelsen]

There is a lot of confusion in your posts, and it's getting to the point where I'm beginning to wonder if you're not taking the mickey.

This for example:

At my fittest point at age 17 I weighed in at 110kgs. Yet BMI scale states I should be 85 kg maximum. Clearly there is an error in my case. Yet the proponents of BMI would have us believe it applies to all Caucasian males and anyone that does not fit this model is overweight. Really? At 110kg I carry a very healthy six pack. As has been mentioned previously for this to occur the body fat percentage has to be about 10%. So again using what I know. This suggests there is an error in the BMI that needs to be considered.

So at 115kg you have 23% body fat, but this drops to 10% if you lose 5kgs? I call BS.

Then there's this nugget:

Weight = 115 kg
B F = 23% - depending on accuracy of measurement maybe 3% less
Muscle mass = 88.55 kg

Your muscle mass is not 77% of your weight. You're overstating it twenty-fold.

Your lack of knowledge about basic human anatomy heavily discredits your opinion about BMI. Personally, I will continue to follow the advice of the World Health Organisation and their ilk, because it is based on science and stuff...

[cp123]

Hell, I'm not a skinny minnie - but nor am I a biggest loser candidate either... but I just love this picture - it says it all really.


Copyright the Willie Wonka and the Chocolate Factory movies.

[Ross]

Cake and eat it too?

Did someone say cake......mmmm cake

[twizzle]

Personally, I will continue to follow the advice of the World Health Organisation and their ilk, because it is based on science and stuff...

... and which is clearly only of benefit when looking at large sample sizes and has no place in the office of a doctor/nutritionist/quack.

Even if it covered 90% of the population with 100% accuracy, you would still have a 1:10 chance of giving useless advice. Last time I was close to my 'ideal' BMI, everyone thought I was anorexic.

[twizzle]

Cake and eat it too?

Did someone say cake......mmmm cake

ROFL, finally - someone who can eat as much cake as they want and it doesn't show.

[rkelsen]

Even if it covered 90% of the population with 100% accuracy, you would still have a 1:10 chance of giving useless advice.

Not me. I'm not a health consultant of any form.

But I'll be the first to admit that I am, on the balance of probability, in the 90% to whom your theory would apply. People seem to be obsessed with "out" groups, and this is a perfect example.

Everyone wants to think that they are in the 20% of the population to whom the BMI scale doesn't apply, when the reality is usually the opposite. It reminds me of this quote:

People are always a tad disappointed when you tell them the standard equipment will suit them quite well.

From this thread: http://www.bicycles.net.au/forums/viewtopic.php?f=12&t=48636.

Call me an idiot if you like, but I have faith in science and I am somewhat disturbed by the fact that so many people seem to be ignoring it (and even trying to refute it if it contradicts their opinions) in this day and age.

[simonn]

Even if it covered 90% of the population with 100% accuracy, you would still have a 1:10 chance of giving useless advice. Last time I was close to my 'ideal' BMI, everyone thought I was anorexic.

If you are worried, go get body fat tests etc from a professional.

What everybody thinks is more likely to be worse than 1:10. The average is overweight now.