what's your REAL BMI??

Discussion in 'Lighter Life Forum' started by roundrachel, 6 February 2009 Social URL.

  1. roundrachel

    roundrachel Silver Member

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    Having been an intrnational athlete and had all sorts of tests done on me in the past I'm always a little wary of the way the LLC works out our BMI.

    Given our body composition is all different it can sometimes be more of a hindrance than a help.

    At present my BMI is 22.2%. according to my LLC. However, having had it done properly yesterday (caliper measurements all over my body etc) it turns out it's 19.1%

    When I weighed 11 stone 10 years ago and was at my fittest, my BMI was 16%. According to the LLC chart that'd make me overweight.

    There are a couple of points I'm trying to make in a rambling way!...

    1. The calculation your LLC uses for your BMI is very crude and gives a guideline BMI

    2. If you're of a certain build (a lot of muscle like me) your BMI will invariably less.

    3. Equally, the BMI you have in reality may actually be MORE than what your LLC calculates it to be.

    4. BMI is a guideline. Your weight may say you're overweight, but if you were to have it worked out scientifically, you may be within the 'normal' category.

    5. Once again, balancing this out, you may officially be 'normal' but your real BMI may put you into the overweight category.

    A heavyweight boxer may weigh 18stone...but will probably have a BMI that'd make him underweight. But by the LLC calculations he'd be morbidly obese!

    All I'm saying it take it with a pinch of salt....or go and get your BMI done by a medical professional (luckily I have easy access to sport scientists in my line of work!)

    It's really interesting stuff.

    Hope I haven't disheartened anyone. Just thought I was a good discussion topic!
     
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  3. bekimo

    bekimo Fighting Demons....

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    I pay little attention to the BMI to be honest. I know that at the size and weight I am, I am not healthy. I also know that Johnny Wilkinson is bloody fit (in every sense of the word) and yet his BMI puts him as obese.

    B x
     
  4. toller-girl

    toller-girl constantly confused

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    I think you're talking about body fat rather than BMI? BMI isn't measured with calipers it's purely a weight/height ratio. It is flawed, but there is also a healthy range rather than an ideal figure.

    It's common sense really, if you're very muscley your BMI probably isn't that accurate, if you're not then it's a good guide to go by.

    It's all just another tool to give us goals and a rough guide to how healthy we are.
     
  5. roundrachel

    roundrachel Silver Member

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    Your BMI is your body fat
    They are one and the same thing. Using calpiers is the accurate way of working it out. Using a chart gives you an estimate but it can be way out depending on your body type
     
  6. Guy

    Guy Likes to lurk

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    I always thought BMI and body fat percentage were two very different things. I could have the same BMI as a rugby player but much more body fat for example. I always thought Body Mass index is a straight comparrisson between hight and weight regardless of fat percentage where as body fat is a completely different measurement process. As an example one of my firends is the same age/sex/height and weight as me. We have the same BMI but my body fat is lower.

    I certainly shifted my focus from BMI to body fat percentage quite some time ago. I;m at 18% now which is borderline healthy for my age/sex. It'll be handy when I get to 30 in a couple of years cos I move into the next bracket. :)

    EDIT: Half decent article about the differencebetween BMI and body fat %

    Body Mass Index (BMI) versus Body Fat

    Body Mass Index (BMI)
    Body Mass Index (BMI) is an assessment of body weight relative to height. Evidence has shown that an elevated BMI increases risk for such diseases as cancer, diabetes mellitus, hypertension, hypercholesterolemia, and atherosclerosis. Research has proven that the higher your BMI, the greater the risk for a premature death. A healthy BMI is 20.0 – 24.9 kg/m 2. A BMI of at least 27 kg/m 2 indicates obesity and increased health risk. A BMI of 30.0 kg/m 2 indicates grade II obesity, while 40.0 kg/m 2 and greater is morbid obesity.

    BMI is the preferred body composition assessment for the obese population because calipers lose their accuracy with large skin folds and variance in fat density. Bio-impedance and near-infrared typically underestimate body fat percentage in this population. Although BMIs don’t account for body fat percentage, excess body fat is already known in the obese.





    Important Limitations of BMI:
    • BMI does not distinguish between fat mass and fat free mass. This is important because ACSM defines obesity as a percent of body fat at which disease increases. People with large amounts of lean tissue may have a high BMI while having their body fat percentage in a healthy range. In addition, a healthy BMI does not necessarily mean that body fat is within a healthy range.
    • BMI does not give any information on the location of the body fat which is important in determining obesity-related risk for disease.

    Body Fat
    Body fat, not weight, is a better measure of your health and fitness. Increased body fat is associated with obesity-related health conditions. Because the scale does not distinguish between lean weight and fat weight, a person could be “over-weight” but not be “over-fat”. However, body fat analysis is not appropriate for people who are obviously obese and tests may not provide an accurate result.
    Body fat can be measured in many ways. The most common methods are skinfold calipers and Bioelectrical Impedance (BEI). Both of these tests should not be done after exercising; BEI results will be greatly affected if you are not properly hydrated. Each method has a margin of error of approximately 3-5%. For skinfold calipers, the more sites that are assessed, and the greater the skill of the person doing the measurement, the more accurate the result will be.
     
    Last edited: 6 February 2009
  7. pete10141748

    pete10141748 Postaholic

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    BMI is not your bodyfat; BMI is your total body weight (hence body mass) calculated by taking your weight in Kilograms and dividing it by your height in metres squared. It is not a percentage of any sort.

    Your body fat percentage is a calcualtion of how much of your body weight is fat cells.


    Unless I've got the complete wrong end of the stick, they appear to be 2 very different types of body analysis to me?
     
  8. PurpleButterfly

    PurpleButterfly 16lb to go!

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    As far as I understood it, BMI serves as a guideline for normal (i.e. not professional athetes) people.
    It is a guideline only, but a useful one if you don't take it religiously.
     
  9. Mini_Me

    Mini_Me LighterLife Returner

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    Hi,

    BMI is a good guide for the general population. It was orginally devised by actuaries (Insurance Companies!) in the US to gauge the risk of their customers. It turned out a pretty good indicator of health risk, so was adopted by many medical organisations...

    BMI is good for the general masses, but not good for athletes. For the reasons people are alluding to above: Athletes tend to have heavier bodies due to increased muscle mass, and less fat, cos they are leaner. BMI would show them as overweight (read: unhealthy) but they are actually very healthy!

    A better guide is your Body Fat... But even with calipers, i wouldn't think that was good for previously obese people, dut to the loose skin... It wasn't a reliable measure for me...

    I use BMI as a rough guide, and pay much more attention to Body Fat measurements (and waist size, to a lesser degree).

    According to BMI, I am overweight at 26. According to my Body fat measurement (14%) and waist size, I'm ok...
     
  10. somewhere_inside_is_me

    somewhere_inside_is_me Silver Member

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    Yes I agree that BMI is just maths. Body fat is something else (but your fancy scales and your callipers won't tell you what fat is around your organs and that's the killer!). The one time I had a sports science style assessment I found my muscle mass is pretty high under all the blubber LOL
     
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