Is BMI the same as body fat% ?

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spatticus
spatticus Posts: 230 Member
in Health and Weight Loss
I have a scale at home that measures my body fat%. Is that the same as my BMI number? Thanks!

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  • SHBoss1673
    SHBoss1673 Posts: 7,161 Member
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    no, BMI is totally different from Body Fat %. but please note, body fat home scales are not very accurate. they use your hydration level, and nobody's the same hydration level every day.
  • spatticus
    spatticus Posts: 230 Member
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    Hmm it also shows me my water % though
  • willimh
    willimh Posts: 227 Member
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    I thought your BMI (body mass index) was your fat percentage. It tells you how much lean you have and how much fat you have. If it's different then what's the difference?
  • Goal_Seeker_1988
    Goal_Seeker_1988 Posts: 1,619 Member
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    I always thought it was, but I could be wrong.
  • givprayz
    givprayz Posts: 328
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    Body mass index is just a ratio of height to weight, nothing more. You can have a normal range BMI and still be higher (or lower) in body fat than is healthy.
  • nantzh
    nantzh Posts: 7 Member
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    BMI is a simple index. I will also add that it is not very accurate on determining the actual fitness/shape of someone. A 6 foot 200 lb body builder and a 6 foot 200 lb couch patatoe would have the same BMI, which would say both were overweight. The body builder though would have a very low body fat percentage, maybe 5%. While the couch patatoe might have a 30% body fat %.

    Basically BMI takes nothing into consideration besides your height and weight. It does not factor in what actualy makes up the weight ( fat vs muscle).

    Hope that helps.
  • SHBoss1673
    SHBoss1673 Posts: 7,161 Member
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    Hmm it also shows me my water % though

    I know of no bio-electrical way to measure hydration. It's probably taking multiple measurements and subtracting. I did a quick search online for techniques to measure hydration without taking urinalysis or blood measurements and couldn't find any. Maybe there is a way, and I just don't know it. It wouldn't be the first time.
  • eillamarie
    eillamarie Posts: 862 Member
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    I have a scale at home that measures my body fat%. Is that the same as my BMI number? Thanks!

    BMI is a completely inaccurate way of assessing your health and fitness. It only works for people of average height and muscle mass. The majority of olympic athletes would be considered "overweight" because they have so much muscle mass that they weight a lot more than the average joe.

    Look @ my picture...I am the tallest one, in the white sweatshirt. I was a national finalist for swimming when that picture was taken...does that look "overweight" to you? Yet my BMI said I was overweight....
  • TrainingWithTonya
    TrainingWithTonya Posts: 1,741 Member
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    No, BMI is a relationship between height and weight and body fat % is an estimate of how much of your current body mass is fat. BMI won't change if you stay the same weight but lose fat and increase muscle, water, or other lean tissue, but your health risk will improve as will your athletic performance and generally, your appearance. While the scales aren't the most accurate ways of determining body fat, they are about as accurate as you can get at home. As long as you are comparing the same type of reading for future comparison, you should be fine with measuring on a scale. The goal will be to have the number go down. But be sure you are checking that water % too. If the water % isn't the same or very close, it won't be an accurate fat % reading.
  • mandykasase
    mandykasase Posts: 110
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    Hmm it also shows me my water % though

    if it's the same one as mine, it's the one that you have to stand on with bare feet at is has these sensor strips for measureing fat%, bmi, water and also bone density.
  • heathersmilez
    heathersmilez Posts: 2,579 Member
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    Are the hand bf calculators that send electrodes through your body more accurate than the at-home feet version?

    The hand-held one is done by a nurse and they warn you not to do it if you are pregnant. The at-home ones don't have that warning so I presume they are less accurate b/c less electrical charge. Also less electrical charge means the % would be calculated on the lowest 1/2 half of your body not the total making it higher correct?
  • TrainingWithTonya
    TrainingWithTonya Posts: 1,741 Member
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    Hmm it also shows me my water % though

    I know of no bio-electrical way to measure hydration. It's probably taking multiple measurements and subtracting. I did a quick search online for techniques to measure hydration without taking urinalysis or blood measurements and couldn't find any. Maybe there is a way, and I just don't know it. It wouldn't be the first time.

    It's estimated through various equations. I've read a couple of studies where they compare the accuracy of bio-electrical impedance analysis (BIA) with other forms of water content analysis and with the right equations it can be pretty accurate. The question is whether or not the scales use the right equations?
  • willimh
    willimh Posts: 227 Member
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    It makes sense. Thanks to all who gave an explanation of the differnce between the two.
  • SHBoss1673
    SHBoss1673 Posts: 7,161 Member
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    Are the hand bf calculators that send electrodes through your body more accurate than the at-home feet version?

    The hand-held one is done by a nurse and they warn you not to do it if you are pregnant. The at-home ones don't have that warning so I presume they are less accurate b/c less electrical charge. Also less electrical charge means the % would be calculated on the lowest 1/2 half of your body not the total making it higher correct?

    I've checked on this before, in general Bio-electrical impedance is the least accurate way to measure body fat percent simply because there's to many ways to screw it up. The conductivity of fat is constant (essentially) so measuring the time it takes to travel a given distance with a known amount of lean tissue and water means you can calculate the fat %, but the problem is, these scales are estimating the givens, I.E. they are estimating the given bone density, and estimating the given lean tissue percent and estimating the hydration level. Now, I won't disagree that companies have become very good at these estimates, but they are still estimating. Any number of factors could cause a false reading.
  • TrainingWithTonya
    TrainingWithTonya Posts: 1,741 Member
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    Are the hand bf calculators that send electrodes through your body more accurate than the at-home feet version?

    The hand-held one is done by a nurse and they warn you not to do it if you are pregnant. The at-home ones don't have that warning so I presume they are less accurate b/c less electrical charge. Also less electrical charge means the % would be calculated on the lowest 1/2 half of your body not the total making it higher correct?

    From my classes we've been taught that the most accurate BIA is the one that attaches an electrode to the and and foot on the same side of the body because it sends the current through what is estimated to be approximately equal to the half of the body that is not being measured. The hand held device actually sends the current through the upper portion of the body and the scale sends the current through the lower portion of the body. Since most people carry more fat in their lower portions (hips and abdomen), the scales will read a higher body fat % then the hand held devices. Neither would be 100% accurate because of not having a whole body picture. As for the current, both the hand held devices and the scales run on a 9 volt battery (at least the ones I've used of both types have), so the current amount is essentially the same. The book that comes with your scale should have some sort of warning for pregnant women and people with pacemakers. I personally haven't read any studies that show a danger to those patients, but its a safety precaution that we're taught to warn people of in the gym setting.
  • SHBoss1673
    SHBoss1673 Posts: 7,161 Member
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    Hmm it also shows me my water % though

    I know of no bio-electrical way to measure hydration. It's probably taking multiple measurements and subtracting. I did a quick search online for techniques to measure hydration without taking urinalysis or blood measurements and couldn't find any. Maybe there is a way, and I just don't know it. It wouldn't be the first time.

    It's estimated through various equations. I've read a couple of studies where they compare the accuracy of bio-electrical impedance analysis (BIA) with other forms of water content analysis and with the right equations it can be pretty accurate. The question is whether or not the scales use the right equations?

    ok that's what I thought. Estimate. I don't doubt that the estimates can be good, the problem I have is that they obviously still have a long way to go. I've seen many different consumer advocacy reports that have given interesting reviews to body fat % scales. things like averaging a 15% margin for error and such. I haven't looked in a while though, maybe they've gotten better in the last year?

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