Yet another weight (mass) question = BMI

Discussion in 'Community Discussion' started by Spanky Deluxe, Jun 28, 2006.

  1. Spanky Deluxe macrumors 601

    Spanky Deluxe

    Joined:
    Mar 17, 2005
    Location:
    London, UK
    #1
    Hi everyone!

    Ok, how much trust do you guys put into the body-mass-index calculators? I put on loads of weight in my first year of Uni and the first summer hols, due to fully carbed hall foods and then a back injury that limited how much moving around I could do (due to pain, nothing serious, all gone now). I'm 6'2" (74"/188cm) and at the end of that Summer I weighed about 16 stone (224 pounds / 102kg). Over the next year I pretty much stayed constant, think I might have lost a bit but then I must have put it back on now that I look back at photos of the beginning of Summer last year.
    I changed my eating habits a bit and since then the weights gradually been dropping off (I haven't been working out loads or anything, just try to eat less crap and more fruit). I've just weighed myself for the first time in ages and I'm down to under 15 stone, about 14 stone 10 pounds (206 pounds / 93.6kg), which is great and I'm pretty pleased. Now I want to lose a bit more but to be honest my biggest aim was to get under 15 stone. I'd like to get to under 200 pounds now I think, about 90kg.
    Now the thing is, that's still classed as 'overweight' according to BMI calculators but the range that they suggest someone my height should be just sounds ridiculously skinny. I'm a broad guy, broad shoulders etc. I don't really work out anymore but I'm stronger than most guys my height. People say that BMI indexes don't depend on build but I can't see how if they are to be accurate that that is true! How can the suggested weights for my friend be the same as for me when although we are both the same height, I am significantly broader than him, I'm not talking fat, I'm talking bones, my shoulders are physically broader than his!
    Also, BMI is supposedly measured in kg/m^2, so its based on area. Surely a broader person has a bigger surface area??

    What do you guys think about BMI calculators.

    Edit: I see that its not based on area but on height squared??
     
  2. jsw Moderator emeritus

    jsw

    Joined:
    Mar 16, 2004
    Location:
    Andover, MA
    #2
    BMI sucks in terms of accuracy. It doesn't take muscle or body type into account.

    If all you consider is weight and height, then a bodybuilder could be considered obese due to the extra density of muscle.

    Body fat is where it's at, but it's hard to accurately measure that on your own.
     
  3. kretzy macrumors 604

    kretzy

    Joined:
    Sep 11, 2004
    Location:
    Canberra, Australia
    #3
    Can't you get scales that allow you to measure this?
     
  4. jsw Moderator emeritus

    jsw

    Joined:
    Mar 16, 2004
    Location:
    Andover, MA
    #4
    Well, I think the whole submerse-yourself-in-a-tank-of-water thing is by far the most accurate. The calipers and what-not for taking your own measurements are not horribly bad, nor are the capacitance-based ones (is it capacitance? maybe resistance...), but they're not all that accurate.

    I think the easiest thing to do is measure the "fattest" part of your waist (typically around the navel for guys) and watch that measurement decline. It's not scientific, but it's a lot better than BMI calculations. If you lose 10lb, you might have lost fat, muscle, or water. If you lose 3" around your waist, well, odds are a big part of that was fat.
     
  5. jelloshotsrule macrumors G3

    jelloshotsrule

    Joined:
    Feb 7, 2002
    Location:
    serendipity
    #5
    yeah, i've found that measuring 0% is super hard to do
     
  6. Lau Guest

    #6
    If you think that you look and feel right, I wouldn't worry too much. I know a couple of people with big shoulders and rib cages who have lost a lot of weight and looked awful at their so called healthy weight. They put a little bit back on and all is good. You're a far better judge of your own health than a table of numbers that are supposed to fit millions of people. I'm feeling pretty lardy at the moment, but I'm not hugely overweight according to government figures. However, I know I need to do something because I don't feel well or look good.
     
  7. Spanky Deluxe thread starter macrumors 601

    Spanky Deluxe

    Joined:
    Mar 17, 2005
    Location:
    London, UK
    #7
    Yeah, I want to lose a bit more but I'm not in a rush. I know that generally speaking if you lose weight fast you put it straight back on again. I think I'll just stick to what I'm doing at the moment, hey I've lost over a stone in a year so I can't be going that wrong!!

    Here's something silly, to be classed as 'normal' according to BMI someone my height would have to be 10.5 stone - 13 stone 12 pounds (147-194 pounds). If I were 10.5 stone I'd literally be skin and bones!! I think my bones probably weigh at least that!!! :p
     
  8. MongoTheGeek macrumors 68040

    MongoTheGeek

    Joined:
    Sep 13, 2003
    Location:
    Its not so much where you are as when you are.
    #8
    I had much the same thought about this until recently. At one point I had a bmi that put me in severely overweight category with maybe 8% body fat (Measured by resistance.)

    The thing is that BMI is an attempt to measure the load on the heart, lungs and kidneys. All of which increase functionality by the square. So if your heart doubles in length the area that blood pumps out goes up by 4 times. If you double everything the length of everything then the amount of tissue that has to be supported goes up by a factor of 8, which means the blood has to come out of the heart twice as fast, meaning the blood pressure and heart rate must go up to compensate. Extra wear and tear on the parts.

    If you look at BMI as a measure of wear and tear then its a fairly good one. If you use it as a measure of fitness/obesity then its crap.
     

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