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BMI

(35 posts)
  • Started 12 years ago by DaveC
  • Latest reply from BikeFan
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12

  1. DaveC
    Member

    No not a Holiday company, but your Body Mass Index.

    Never having done anything about my weight for years I started noticing my weight has come down from ~15.5 st 2 years ago to 13st now, since I started cycling.

    Mark Beaumont has tweeted this:

    http://www.bbc.co.uk/news/health-18770328

    Now I'm 40yrs, Male, 163cm, and 13st. BBC's Calc gives me a BMI of 24. What are you? Are you 'bovered'?

    From the Beeb website:
    Measure of weight relative to height
    Calculated by weight in kilogrammes divided by height in metres squared.
    A BMI of less than 18.5 is underweight
    A BMI of 18.5-25 is ideal
    A BMI of 25-30 is overweight
    A score of 30 or above is obese

    Posted 12 years ago #

  2. BenN
    Member

    I have had a wee play with this as well (bang on 25 for me), and it was lovely to see that I was lower than 75% of the population of the UK, and am indeed more akin to a resident of South Africa.

    Simple caveat here though - BMI is a function of height vs weight vs sex. For active individuals such as the majority of board members here, a higher percentage of body weight may come from muscle, thus it cannot entirely be relied upon. To take this to its extreme, I once heard an anecdote about a serious rugby player who was refused entry to the Army as his BMI was over 30%, even though his body fat was incredibly low. True or not, it highlights the point well.

    As a side point, and because every now and then someone needs to say it to remind you - well done on the weight loss! You are healthier, probably feel a lot better about yourself, will hopefully live longer and draw less resources from the NHS and in turn the taxpayers' purse.

    Posted 12 years ago #

  3. Uberuce
    Member

    The BMI is the Bee in My bInnet.

    Silly clumsy exception-laden pile of guff that only becomes a measure of health at the extremes, by which point it's irrelevant because you don't need a number to diagnose starvation or morbid obesity.

    It reports anyone with any degree of muscle mass as overweight, which due to the vastly increased level of weight training in the populous is a lot of folk, and givs skinnyfat people the mistaken belief that their 25+ fat percentage is okay because their BMI is 20-25.

    This is me at a BMI of 32: http://t.co/Wyu3fAtL

    Not six-packed, I concede, a month of beerless would have got me there.

    Posted 12 years ago #

  4. Morningsider
    Member

    "You are most like someone from North Korea" - not something you hear every day! I think BMI is probably a useful measure on a population scale rather than for individuals - uberuce obviously proving the point.

    Posted 12 years ago #

  5. Uberuce
    Member

    I think BMI is probably a useful measure on a population scale rather than for individuals

    That is the wings of my bonnet's bee - I contend that it is useless even here. It'd be better if the Department of They stopped pretending the easily measured BMI is valid, and just admitted the problem they're trying to quantify is going to need more work to get good data on.

    Posted 12 years ago #

  6. SRD
    Moderator

    I regularly tell my North American friends who are dieting that BMI is rubbish and they they should just lead more active lives./

    But anyway, I'm a 21 and "have less body fat than 90% of females aged 30-44 in your country". hee hee!

    Okay, glee aside, I am not particularly skinny. I am relatively small yes, but not skinny. and still lots of post-baby fat left. makes you wonder, eh?

    Posted 12 years ago #

  7. lionfish
    Member

    Although BMI has failings I think dismissing it to that extent is unwarranted. It has considerable use. For instance, combined with mid-upper-arm-circumference (MUAC) it plays a very useful role on an individual-by-individual basis in emergency feeding during food insecurity. I read a recent paper comparing MUAC and BMI. MUAC did better at predicting morbidity/mortality (this is again at the bottom end of the scale), but BMI did very well too, and requires considerably less expertise from the people doing the measurements.

    The large range of values for a healthy BMI are because it's not very accurate. Still, to get to 'overweight' I'd have to put on 16kg (2.5stone), and to get to the 'obese' category I'd have to put on 5 stone.

    Posted 12 years ago #

  8. Morningsider
    Member

    Uberuce - I did say "probably"! Honestly, after years working in the public sector do you think I am capable of writing something that would hold me to a particular opinion.

    Posted 12 years ago #

  9. Min
    Member

    Of course BMI is not perfect but you only need to go outside and look at people to see that the 2/3 or so of the population with a BMI of over 25 match uncannily with the 2/3 or so of people who are carrying too much fat.

    Posted 12 years ago #

  10. SRD
    Moderator

    I was a control in a study about obesity in pregnancy, which was very interesting. They have a nifty device that looks like a normal scale that you stand on, but which actually tells you what % of your weight is fat. This seems much more relevant to me. Wish I knew how it worked though!

    Posted 12 years ago #

  11. wingpig
    Member

    "Wish I knew how it worked though!"

    Conductive footpads to measure the speed of conduction through the body, though I don't know if such scales control for different leg lengths...

    Posted 12 years ago #

  12. 14Westfield
    Member

    With a BMI of 29 i'm (apparently) most like a Samoan, which kinda suits me fine as it is rugby rather than a predilection to pies that has got me there!

    Posted 12 years ago #

  13. Smudge
    Member

    @BenM your anecdote is not untrue, I'm aware of a fit forward (though not really a "serious" rugby player)who was training regularly and lucky if he was carrying more than a pound or two extra, over BMI, deferred until he lost weight. Madness!

    I'm 5'5" and ten and a half stone (43 year old bloke, though I don't know if that is supposed to be included in the calcs), the online calculator isn't working for me, but using the folrmula above, if my sums are correct, my BMI is 24.5 so I'm allegedly on the cusp of overweight... yet every medic who's ever assessed me as said my weight is well within an acceptable range and I pass my fitness tests comfortably.

    In my unqualified opinion BMI is so unreliable as to be utterly worthless for assessing individuals. It makes as much sense as saying "eat less fat and you'll be healthy", there are far too many other factors for it to be a valid measure in isolation.

    Posted 12 years ago #

  14. lionfish
    Member

    Smudge: I don't quite get the issue; you're in the 'not overweight' category and the medics also said you're not overweight. Doesn't that sort of tally :-. ? If you had a BMI of 33 and the dr said your weight was fine, that would indicate the BMI measure wasn't working.

    I figure it might not apply to 100% of the population, but if it works well for 98% then it's pretty good?

    I'll have to get minimoth who has a Masters in public health nutrition to 'weigh in' on this one [pardon the pun]

    From my understanding of what she's said, to be healthy you should try to follow the following:
    1. do exercise, make it part of your daily routine.
    2. eat a balanced diet, based on the proportions on the eat well plate (i.e. lots of complex carbohydrate, lots of veg+fruit, and a little bit of dairy, meat, and a tiny bit of sugary fatty food...)
    http://en.wikipedia.org/wiki/Eatwell_plate
    3. don't smoke (or drink really excessively regularly).
    4. spend time every day with people you like.

    Posted 12 years ago #

  15. wingpig
    Member

    BMI possibly has a slight usefulness as a means of helping to convince some genuinely too-much-fat people that they are really genuinely carrying too much fat. Look! It's sciencey and has a superscripted numeral in the formula and everything!

    I can generally tell by looking/prodding whereabouts I am in the relatively narrow range of masses I've inhabited throughout adulthood (so far) and can similarly assess whether differences are due to muscles or muffins. The couple of times when I've felt slightly jiggly when trotting up stairs have resulted in taking up running or going for extra bicyclings until it stopped.

    Posted 12 years ago #

  16. ExcitableBoy
    Member

    DaveC, 163cm is about 5 foot 4, perhaps your 183cm?

    Posted 12 years ago #

  17. Smudge
    Member

    My problem with my own example is that I ought to be pretty average, yet I'm at the outside edge of the (wide) acceptable range.
    My workplace is hampered by a policy that potential employees must be within the "ideal" limits to be accepted due to the potential physical demands of the job. This has resulted in the people recruiting employees regularly being frustrated by healthy individuals who fall just outside the proscribed limits. Indeed a doctor I met described the measurement as "an unreliable box ticking exercise which we should never have adopted".
    I'd be very surprised if it works for 90% of the population, I'd suspect somewhere below 80% based on my own experiences. But that is only guesswork so I'd be delighted if anyone has proper statistics to prove my fears unfounded!

    Posted 12 years ago #

  18. Greenroofer
    Member

    I'm a 23, which is interestingly close to the upper limits of what is 'OK'.

    Since I took up cycling to work regularly I've put on about 3kg, taking me from 71 to 74kg. My trousers are definitely a lot tighter round the thigh than they used to be, but they are also tighter round the waist, so I could just be fat. However, with a weight of 71kg, my BMI would be 22.

    I've always thought of myself as being skinny (until recently I've bought trousers with a 30" waist!), so I'm surprised to have such a relatively high BMI. I know it's lower than most of the population, but it's higher than I expected. It doesn't make me out to be the bag of bones I expected.

    Maybe I'm actually a 'muscular athlete'...

    Posted 12 years ago #

  19. DaveC
    Member

    @ExcitableBoy aye I'm 183 not 163, mistyped.

    Posted 12 years ago #

  20. ARobComp
    Member

    27 - hah.
    I am 97kg and 6'3''
    I have a 34 inch waist
    I train 5 times a week and am fitter at the moment than I have been for ages.

    I was actually rejected from the TA earlier this year because of my BMI despite the fact that I passed the fitness stuff with ease. They told me to come back when my BMI was below 25. I pointed out that if I stop exercising completely I'd lose about 3-4 kg in a few months and wondered whether that was preferable for them...

    Posted 12 years ago #

  21. fimm
    Member

    I get the impression that BMI is a problem for well-muscled males (even those not quite as scary-looking as Uberuce...). I hear less from women falling foul of it.

    One of my colleagues was saying just the other day that he'd been measured and his BMI had gone up, and in the past he'd not been too bothered about BMI because he used to do judo and stuff and was generally fit; but now he was having to admit that his "muscle" was actually on his waistline...

    On, mine is 20 or so. If my recollection of my weight and height at age 18 is correct, I was underweight - but I don't think that should be too concerning for an active teenager. It might be different if I went back to that sort of shape now!

    Posted 12 years ago #

  22. Arellcat
    Moderator

    Conductive footpads to measure the speed of conduction through the body, though I don't know if such scales control for different leg lengths...

    It's known as bioelectrical impedance analysis. The premise is that the body's resistance to current is proportional* to the total amount of water in the body, and from this you can calculate reasonably accurately the fat-free mass in the body. By taking the difference between the fat-free mass and your total body mass, you have your body fat mass and you can convert that to a percentage of the total.

    The consumer devices are only so accurate because the AC current flows from one foot to the other (or in the Playstation controller-style ones, from one hand to the other) so the other half of the body is disproportionately ignored.

    My crude BMI comes out at 22.3, which I think is ok. I do have more fat than I'd like, though.

    * additional factors in the analysis include sex, age, weight and height, generalised for statistically similar populations.

    Posted 12 years ago #

  23. lionfish
    Member

    Ok, I'm starting to be convinced that maybe the issues of people doing a lot of heavy training are a problem for the BMI assessment (I still think that'll only be a few % - this forum is not a fair sample of the population). I would hope that for something like joining the TA etc they would use a more complete way of measuring an individual's health/fitness. But I still think it's pretty useful for the majority of the population who do very little exercise. Importantly, if it is an issue around people doing heavy training then I'd have thought the entry requirements to the TA would be a bit more sensible. If it's for whether to refer someone to a dietician checking if their BMI>40 (morbidly obese) might be a useful cut-off. But clearly no one should use a metric like this without taking other things into account, for an individual (e.g. what other morbidity is the person suffering from? what underlying cause is there to the weight-gain?).

    The proportion of people in Scotland with a BMI>30 has gone from 17.2% in 1995 to 27.4% in 2010. I really doubt that that is due to 10% of the population taking up serious muscle building regimes[1].

    Critcally, if you really think that BMI has no strong association with health, why is it that it is hugely correlated with a massive variety of diseases[2]? It seems a little silly to throw out the whole metric because it's not perfect - no measurement of a population is ideal (either it will be too expensive/impractical/inaccurate/etc..). Obviously subjectively you can say 'woah, that person's big' or 'shesh, you're skinny', but it's very useful to have a quantitative measure of that.

    Summary: I agree it doesn't work for everyone, but why dismiss it so completely? People seem to be applying it badly. Which is a fair enough criticism. Also being in the 'overweight' is barely of any concern - concern about being 1.7 over the 'threshold' is missing the point. The thresholds are basically useful tools for researchers/clinicians but shouldn't be abused (e.g. maybe like the TA did).

    [1] Scottish Health Survey 2010.

    [2] http://en.wikipedia.org/wiki/Obesity-associated_morbidity
    (that is a pretty depressing page...).

    Posted 12 years ago #

  24. recombodna
    Member

    23.4

    Posted 12 years ago #

  25. steveo
    Member

    I'm a big 'ole Samoan according to the beeb... 29! At least if I was Samoan i'd be big boned instead of heavily beer bellied!

    Posted 12 years ago #

  26. Smudge
    Member

    @Lionfish, yup pretty much agree with you there, not "just" the TA incidentally, the entry requirements for TA or regular Army service are identical these days.
    Doesn't mean to say that anyone in a large(ish) organisation can apply common sense of course!

    damhikijkok ;-)

    Posted 12 years ago #

  27. kaputnik
    Moderator

    Brunei. The Sultan I hope.

    Posted 12 years ago #

  28. DaveC
    Member

    @arellcat said "* additional factors in the analysis include sex, .....

    [sound of turntable arm being ripped from vinyl!!!]

    So if I double the number of times I have sex with the missus my weight could fall? I'd better buy that extra condom a quarter then... ;-)

    (no smutty jokes about sex outwith the missus please... ;o)

    Posted 12 years ago #

  29. recombodna
    Member

    ....cleans tea from screen......

    Posted 12 years ago #

  30. Arellcat
    Moderator

    Now now, boys, behave.

    Posted 12 years ago #

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