BMI - All Its Cracked Up To Be?

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BMI - All Its Cracked Up To Be?

Postby dynamictiger » Fri May 11, 2012 2:55 pm

As I suggested in another post, I have seen several threads degenerate into discussions, albeit at times fiery, on the merits and failings of BMI.

Rather than let this continue unabated to dominate other threads on more weighty (pun intended) issues, I thought it may be a good idea to start a thread to specifically discuss it.

I would really appeal to all posting to this thread to be polite to each other and whilst disagreement and argument is at times potentially helpful, to please try and keep it reasonable.

I will kick it off by stating I do not agree with BMI. I think it is absolutely nonsense in my specific case, and before I get flamed to death for that statement, my Doctor agrees with me. In researching why this was, and why the BMI seemed so out for me I realised it was worked out in a country that has no bearing at all on my heritage in the last 5 generations, was designed prior to the country I was born in being discovered, does not acknowledge or allow for my width of back/shoulders and therefore cannot be accurate. A little like saying a pool of 3 metres length and 2 metres width must always contain 6000 litres. This is based on assumption that may or may not be true.

For the record I am 185 cm tall and 115-117kgs, although I would like to get to 110 kgs, it is looking like a very illusive target. According to BMI my target weight is 85 kg. As I have said previously of my BMI weight target...oh yeah, and what happens when I turn 10?
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BMI - All Its Cracked Up To Be?

Postby toolonglegs » Fri May 11, 2012 3:09 pm

Post a photo of your body ... We don't need BMI to tell us what is healthy and what is not.
BMI is very good for me ( 194cm ex #8 rugby player ) At 30 BMI I am fat, 25 I don't look fat but am still carrying too much... At 22.5 I am flying.
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Re: BMI - All Its Cracked Up To Be?

Postby rkelsen » Fri May 11, 2012 3:40 pm

I've been contemplating starting a thread along these lines for the past few days, but wasn't quite sure how to do it.

Back when I weighed 116kg, I was a "BMI denier" as well. Now that I'm down to 92kg and still have 27% body fat, I can see that the BMI scale does have merit. My goal is to get to 20% body fat. If I do that, then I have no doubt that I will be within the healthy weight range of the BMI scale.

The reason that the World Health Organisation still persue the use of the BMI scale is that real data continues to support its use. Take the following graph for instance:

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That data is from a sample of 8,550 American males taken in 1994.
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Re: BMI - All Its Cracked Up To Be?

Postby datanerd » Fri May 11, 2012 4:17 pm

It's probably fair to say that it's a reliable guide for most people, but like anything statistical there will always be outliers/exceptions, plus as OP pointed out - it can't necessarily be transferred to people from a different genetic heritage. Historically, in a similar fashion, IQ tests were problematic because of cultural differences.

That said, being an average kinda white guy, I'd be deluding myself if I tried to convince myself that I was "big boned" or something to the extent that I fall outside the "norm" that BMI is based on. Being 178cm, my healthy weight range is from 60-79kg. I'm currently 91kg or so (from a high of 109kg), so my BMI is currently 28.7, and looking in the mirror it's clear that I still have weight to lose. However, I do believe I'm "stocky" for my height, and carry a larger muscle mass, so I doubt whether I could realistically ever get down to below 70kg. Anything's possible, but I'd have to atrophy a lot of muscle as well as losing fat. But getting to a BMI of less than 25 should (hopefully) be eminently achievable for me.

BMI is just one statistical tool that doctors and other health professionals use, and it's probably good for most people. One would hope that a doctor would disregard it when faced with someone who obviously does not fit within the statistical "norms" for BMI. There's plenty of other tools, like body fat %, waist measurements, heart rate and blood pressure that can be used to build a picture.
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Re: BMI - All Its Cracked Up To Be?

Postby DaveOZ » Fri May 11, 2012 4:27 pm

BMI is a realistic guide for most people with your body type determining which end of the scale you should be.

Most people could however have a good hard look at themselves in the mirror and know if they are overweight or not. If not, just post a picture on here and I'm sure many would be glad to critique your proportions.
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Re: BMI - All Its Cracked Up To Be?

Postby lethoso » Fri May 11, 2012 8:29 pm

oh hey a statistical measure is inaccurate with a sample size of one, who would have thought :roll:
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BMI - All Its Cracked Up To Be?

Postby scotto » Fri May 11, 2012 9:19 pm

BMI us generally a reasonable measure though not always reliable. Measure most professional footballers (real ones, not the backs !!) and they will be ranked obese . Or closer to home, the Fat mans wheel race on the RAW series is based on BMI. More than a few riders qualified but were 'encouraged' not to riders there BMI may have been enough but the obvious lack of body fat suggested entry may not have been in the spirit if racing...
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Re: BMI - All Its Cracked Up To Be?

Postby vander » Fri May 11, 2012 10:27 pm

BMI is a rough figure that is all. I dont really like it personally but for big groups of people its not too bad. For health outcomes fat%age is not that great as subcut fat does not have much impact on health. It is also a population measure on the whole population it works pretty well individually its pretty poor, eg Shane Perkins is about 180cm and around 95kg which puts him close to Obese which he certainly isnt.
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Re: BMI - All Its Cracked Up To Be?

Postby toolonglegs » Fri May 11, 2012 10:36 pm

Yeah but if you had a body like Shane's you wouldn't be worrying about your BMI...
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Wiggo is on the absolute minimum of the BMI healthy scale (well according to Sky's website, but we all know climbers never give their real weight)
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For most of us normal people it gives us a rough idea... but then so do love handles, muffin tops and man boobs
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Re: BMI - All Its Cracked Up To Be?

Postby vander » Fri May 11, 2012 10:48 pm

Wow Wiggo looks so gross. He doesnt seem that skinny on TV surely he isnt.
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BMI - All Its Cracked Up To Be?

Postby donncha » Fri May 11, 2012 11:35 pm

You're not fat, you're just big-boned :)

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Re: BMI - All Its Cracked Up To Be?

Postby wombatK » Fri May 11, 2012 11:43 pm

dynamictiger wrote:For the record I am 185 cm tall and 115-117kgs, although I would like to get to 110 kgs, it is
looking like a very illusive target.

You don't need to debate whether BMI is right or wrong, but rather, why losing
5 kg is a very illusive target. At worst, that's a dreadful self-fulfilling prophecy.

At best, why waste time thinking about whether the BMI is valid or not, if
you're real issue is that you'd like to lose 5Kg but can't ?

There is a good Zen proverb that goes something like "when the pupil is ready, the
teacher will arrive". Until the pupil is ready, all we can do is kill you with kindness
by agreeing with your trashing of BMI.

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Re: BMI - All Its Cracked Up To Be?

Postby Meditator » Fri May 11, 2012 11:51 pm

Wiggo is certainly anorexic. He looks positively deathly. Whoever he is.

About BMI, i agree iwth the first poster. Its usualy obvious if BMI isn't going to apply to you. It works fine for me.

It would be helpful to say what your ancestry is given that you don't want to post a picture of yourself.
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Re: BMI - All Its Cracked Up To Be?

Postby dynamictiger » Sat May 12, 2012 9:01 am

wombatK wrote:You don't need to debate whether BMI is right or wrong, but rather, why losing
5 kg is a very illusive target. At worst, that's a dreadful self-fulfilling prophecy.

At best, why waste time thinking about whether the BMI is valid or not, if
you're real issue is that you'd like to lose 5Kg but can't ?


Sorry for not being sufficently clear. The apparent reason I find the last 5 kgs so illusive is as I am on a high protein diet, I start to loose say about 2-3 kgs in a few weeks, then as I exercise so much I am gaining that back in muscle within a few more weeks as my muscle mass keeps going up.

Again the reason I started this thread was to provide a place for all the BMI posts to come together, rather than hijack other threads as has happened in the past.
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Re: BMI - All Its Cracked Up To Be?

Postby foo on patrol » Sat May 12, 2012 9:42 am

For my way of thinking......you cannot blanket cover everyone with the same measurment stats from this so called be all and end all of readings. It doesn't take into account body structure, as in bone size. This is why I think you need to carefull of how you use it and how you taylor your eating and exersice habits. :idea:

Those that fit the so called ideal frame and body type, well and good but use it only as a guide, not gospel. :wink:

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Re: BMI - All Its Cracked Up To Be?

Postby simonn » Sat May 12, 2012 10:04 am

I am 173cm and ~76kgs which puts my BMI as 25.something (and I could lose some flab). For my height, the good range of BMI spans ~19 kgs which is > 20% of my current body weight. This is a huge span! IOW, BMI leaves a hell of a lot of wiggle room.

Dynamictiger, you may be one of the few percentile of people that does not fit within the BMI. However, the way to use BMI (for everyone) is to determine your BMI and if you do not agree with your results and/or are worried about them you can go to a doctor and do more accurate body fat and general health tests etc.

For most people, BMI, a bit of honesty and not comparing yourself to the average person (who is overweight now) will be enough. In fact a comparison the average person is pretty much the worse thing that can be done and is considered a confounding factor of the obesity problem.

At the end of the day weight is only one part of the puzzle anyway.
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Re: BMI - All Its Cracked Up To Be?

Postby vander » Sat May 12, 2012 11:10 am

simonn wrote:I am 173cm and ~76kgs which puts my BMI as 25.something (and I could lose some flab). For my height, the good range of BMI spans ~19 kgs which is > 20% of my current body weight. This is a huge span! IOW, BMI leaves a hell of a lot of wiggle room.

Dynamictiger, you may be one of the few percentile of people that does not fit within the BMI. However, the way to use BMI (for everyone) is to determine your BMI and if you do not agree with your results and/or are worried about them you can go to a doctor and do more accurate body fat and general health tests etc.

For most people, BMI, a bit of honesty and not comparing yourself to the average person (who is overweight now) will be enough. In fact a comparison the average person is pretty much the worse thing that can be done and is considered a confounding factor of the obesity problem.

At the end of the day weight is only one part of the puzzle anyway.


Ill start with your point to go see a doctor. In my opinion doctors are useless at anything health related unless you have a very good one they know next to nothing infact they are a big problem with pushing this population measure as an individual measure which it is not. GPs are only really good for a few things, getting anti-biotics (though some you have to say you want anti-biotics or they dont give them to you) and referrals to someone that knows something. This is my 2c.

Another point, a bit of flab is normal, a lot of people arent meant to be walking around with 6packs and maintaining that sort of weight for them is unhealthy and unsustainable. However you shouldnt have much more fat.

BMI is next to useless on the individual level the reason it works on populations is after you average up everyone you get the average bone structure and average muscle mass etc so then it is a decent predictor but there is such a wide variety between individual people that doing it on individuals is a joke.

Your last point is very correct weight is only part of the puzzle. There are much bigger things at play in someones health and having weight and height as the only 2 items used in an equation and then coming up with a health status (which is what these people take it as) is ridiculous.
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Re: BMI - All Its Cracked Up To Be?

Postby dynamictiger » Sat May 12, 2012 11:43 am

vander wrote:Another point, a bit of flab is normal, a lot of people arent meant to be walking around with 6packs and maintaining that sort of weight for them is unhealthy and unsustainable. However you shouldnt have much more fat.


This is pretty well where I sit. I have a three pack descending to a six pack depending on day of the week, exercise for the day and so on.

One of the reasons I am not a fan of BMI is one of my Doctors told me I was massively overweight and that I have to get my weight down to 85 kg. I asked him why. He told me BMI was the reason. I then asked him okay so what happens when I turn 10? He had no answer for me.

My new Doctor is more sensible and also charges a lot more. He is very happy with where my weight is sitting now. I am the only one that would like to see if I can loose a few more kilos...then I can have a six pack permanent :D :D
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Re: BMI - All Its Cracked Up To Be?

Postby Meditator » Sat May 12, 2012 2:39 pm

Your last paragraph shows why your last doctor agrees with you. He's taking a lot of money from you so he doens't want to disagree with you.

The point is not whether BMI is going ot help you or not but are you over weight. Have you tried to measure your body fat. Why don't you try that. There's a number of formulas on the web and indicators of how much body fat is in hte normal range. If your body fat is greater you will know you are fat.

Also if you are putting on lots of muscle then of course your weight will be up.

I think you are being obsessive about this and that's not so healthy.
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Re: BMI - All Its Cracked Up To Be?

Postby dynamictiger » Sat May 12, 2012 3:22 pm

Meditator wrote:The point is not whether BMI is going ot help you or not but are you over weight. Have you tried to measure your body fat. Why don't you try that. There's a number of formulas on the web and indicators of how much body fat is in hte normal range. If your body fat is greater you will know you are fat.


Currently it is 23%.
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BMI - All Its Cracked Up To Be?

Postby toolonglegs » Sat May 12, 2012 4:31 pm

How can you have a 6 pack some days of the week at 23% body fat?.
You obviously aren't a competitive cyclist so you must be doing gym work or something else sport wise for training to be putting on muscle?.
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Re: BMI - All Its Cracked Up To Be?

Postby vander » Sat May 12, 2012 4:57 pm

dynamictiger wrote:
Meditator wrote:The point is not whether BMI is going ot help you or not but are you over weight. Have you tried to measure your body fat. Why don't you try that. There's a number of formulas on the web and indicators of how much body fat is in hte normal range. If your body fat is greater you will know you are fat.


Currently it is 23%.


You cant be 23% and have abs. It is well outside the normal range. Unless you have a lot of fat on other parts of your body which to this degree is very unlikely. I am about 12-15% body fat and am lucky to see an ab (I have had it tested when I had 1 or 2 and I was 9%). About 10-12% is when you stat to see abs, so maybe get it tested again. Another thing to note if you are tested with calipers there is a bit of error with them it very much depends on the skill of the tester.
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Re: BMI - All Its Cracked Up To Be?

Postby simonn » Sat May 12, 2012 5:44 pm

vander wrote:In my opinion doctors are useless at anything health related unless you have a very good one they know next to nothing...


Perhaps I should have said "seek medical advice" instead of go and see a doctor.


vander wrote:Another point, a bit of flab is normal, a lot of people arent meant to be walking around with 6packs and maintaining that sort of weight for them is unhealthy and unsustainable. However you shouldnt have much more fat.


However, I am pretty certain that the majority of people who have a bit more than a bit of flab are well outside of the normal BMI range. See my point above. On the muffin top scale, I fail, oh so slightly, but I could eat less pies.

BMI is next to useless on the individual level the reason it works on populations is after you average up everyone you get the average bone structure and average muscle mass etc so then it is a decent predictor but there is such a wide variety between individual people that doing it on individuals is a joke.


Again, the the normal range is a quite a large range, > 20% of my current very slightly above the normal range weight for me. Again, if someone is honest with themselves and thinks that they are a statistical anomaly they can seek further medical advice, do tests etc.

Your last point is very correct weight is only part of the puzzle. There are much bigger things at play in someones health and having weight and height as the only 2 items used in an equation and then coming up with a health status (which is what these people take it as) is ridiculous.


Of course. The BMI is just a quick simple easy to calculate way of determining what weight range you should probably fit in. Nothing more nothing less.
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Re: BMI - All Its Cracked Up To Be?

Postby wombatK » Sat May 12, 2012 7:25 pm

dynamictiger wrote:Sorry for not being sufficently clear. The apparent reason I find the last 5 kgs so illusive is as I am on a high protein diet, I start to loose say about 2-3 kgs in a few weeks, then as I exercise so much I am gaining that back in muscle within a few more weeks as my muscle mass keeps going up.

OKay, so the big issue is the yo-yo-ing weight and lack of six pack definition you crave.

Nobody ever claims that BMI is capable of distinguishing between weight gain due to muscle building and that due to fat building - it isn't cracked up to be that by anybody. So it isn't going to help you lose the 5 kg and/or enhance your 6-pack or explain your yo-yo-ing.

For that, you need to work out what is making your body switch from fat-stripping to muscle building every alternate few weeks. Do you slack-off your exercise for those, and them ramp it up for a few weeks ? Or is the food-intake changing, or is it both ? Did it do that for all those years it took you to get from a 3 kg bub to your present 115 kg plus state, and if it didn't, what changed ?

Unstable Yo-yo-ing like you describe is a sign that your diet and exercise program is not well controlled. Maybe you need to work out how to bring it under control. For both men and machines, unstable control arises due to the absence of timely and appropriate feedback. Closer monitoring and tools like regular skin-fold tests (by a qualified practitioner) are what elite athletes use to make sure they are putting on muscle rather than fat; its the feedback they get to prove whether they are eating too much wrong stuff or not.

Other tools like keeping food (and drink) diaries, and detailed records of your exercise sessions and other incidental exercise can also be helpful in identifying what changes between your fat-stripping and muscle building weeks - provided you can be brutally honest and very diligent about it (lots of people can't).

If you want to go down such a path, most accredited dietitians are experts at skin-fold tests, as are a other allied health specialists such as exercise scientists and sports physio's. And they cost rather less than consultations with doctors, and generally have much more time to spend with you and explain the messages fully.

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Re: BMI - All Its Cracked Up To Be?

Postby ColinOldnCranky » Sat May 12, 2012 7:49 pm

I have always understood that it's proper use is restricted to demographics, not to individual. Nevertheless as we all know many professed "health professional" services have used it exactly for individuals despite there far better tools all the way down to a simple skin-fold test. ANd t hose stupid scales that include a BMI based assessment should be outlawed.

As a demographic tool it is great. But even then an analyst should still look deeper. What would it show if the retirement village industry started a very broad practice of working out their clients in a gymnasiums for example? That the old people under their care are becoming even less healthy?

If you have a swimming pool try floating for a minute. I had great difficulty in passing that bit of my swimming silver medal when I was young and a rippling gymnast. I am tempted now to try it again, confident that I would still find it difficult. :) Most of my friends did not have the same difficulty and regretably they would have even less difficulty now.

Cyclists on this thread would tend to be better I expect than the normal demographic. Now that would be a more interesting push button questionnaire for someone to start up. Respondents to tick of their weight, height, gender and age and tehn compare it to norms. Probably though the more healthy would be inclined to take the survey so there would be the issue of population bias.
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