Question About Body Fat Percentage Calculations

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Sunny_fit4life
Sunny_fit4life Posts: 157 Member
in Health and Weight Loss
I have a question regarding body fat percentage calculations. I have used different methods to calculate and gotten very different answers. In case you're wondering I am getting these formulas from fat2fitradio.com because I was linked there by someone here.

The Military BF% Calculation tells me my BF% is 51.5%
The "Covert Bailey" Formula (from the author of the Fat 2 Fit book they're promoting) gave me an answer around 31%, although that seemed ridiculously wrong so I didn't write it down.
I assumed the Military BF% was more accurate, so I'm really just saying this part for background info.

They assert that you should set a body fat percentage goal instead of a weight goal and then give you a chart of what body fat percentage is healthy for your age and gender. There is also a calculator to determine your goal weight based on current weight, current body fat percentage and your goal body fat percentage. You can find it here:

http://www.fat2fitradio.com/tools/ibw/

Here's the real question and it may be a dumb question, but science & math are my weak points...

What I want to know is, how on earth do they know what your body fat percentage would be at a certain weight? I don't understand that. Isn't this completely inaccurate, or is there any validity in it?

Also, I have heard criticisms of BMI as a measurement as well. How do you gauge your goals? How do you know when you are at "a healthy weight"?

I know that was a long post for a short question, but I was hoping one of you lovely MFP'ers that likes to offer help on the message board would be so kind as to explain a little more about this.

Replies

  • Sunny_fit4life
    Sunny_fit4life Posts: 157 Member
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  • CristinaL1983
    CristinaL1983 Posts: 1,119 Member
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    Basically, when they calculate the body fat measurement, it should also give you a lean body mass. So let's say (for the sake of having numbers) a person weighs 200lbs and is 50% body fat. So it should tell you that your lean body mass is 100 lbs. If you were shooting for a body fat percent of 20, you would use this equation 100/(1-.2) which would give you an estimated goal weight of 125 lbs. You can verify that you have the right number by subtracting lean body mass from it and dividing the resulting fat mass by total weight. So in this case 125-100=25 25/125=.2 (or 20%)

    So the initial equation is lean body mass/(1- desired fat percent as a decimal)
  • Sunny_fit4life
    Sunny_fit4life Posts: 157 Member
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    Thanks for the explanation on the calculation... My concern is that the weights that I'm given with these calculators as being "in the healthy range" are about 15-25 lbs higher than what I'm told is in the "healthy range" by the measurement of BMI. The BMI chart says I should weigh under 140 and the calculations I got with estimated body fat percentage say I should shoot for 155-165. I'm only 5'5". I'm really curious on what the best/most accurate ways to set goals would be.

    I don't consider myself particularly muscular. I carry most of my excess weight in the tummy, which is actually really disproportionately large for my figure.
  • CristinaL1983
    CristinaL1983 Posts: 1,119 Member
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    If I remember correctly, on that website it lists up to 31% body fat as being healthy. IMO, that's pretty high. I'm at 25% body fat right now and still above my healthy BMI. I'm shooting for 20% body fat which will put me at a shape that I want and within my healthy BMI.

    I'm 5'7'' so my healthy weight range is a little bit higher than yours but I have a "large frame" and am pretty muscular (122 lbs lean body mass) so I have always been in the top part of my "healthy range."

    BMI is a good general tool or a good tool for population calculations but it is not great for individual calculations.

    I'm more concerned with body fat than BMI.
  • Sunny_fit4life
    Sunny_fit4life Posts: 157 Member
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    If I remember correctly, on that website it lists up to 31% body fat as being healthy. IMO, that's pretty high. I'm at 25% body fat right now and still above my healthy BMI. I'm shooting for 20% body fat which will put me at a shape that I want and within my healthy BMI.

    I'm 5'7'' so my healthy weight range is a little bit higher than yours but I have a "large frame" and am pretty muscular (122 lbs lean body mass) so I have always been in the top part of my "healthy range."

    BMI is a good general tool or a good tool for population calculations but it is not great for individual calculations.

    I'm more concerned with body fat than BMI.

    Going by their calculations on this site, my lean body mass is around 120 lbs. Also their "healthy range" of 21-33% would mean I should weigh 152 - 179 at 5'5". A BMI chart says I should weigh 114-149. I really have no frame of reference because I've been 172 at the very lowest in my adult life. Before I gained weight b/c of medication around the age of 16 I was always 110-130, constantly fluctuating at about 5'3". But I was a teen so there's no comparison. Originally I had my weight goal set at 125 thinking because I weighed around this as a teen it would be a good weight for me. Since I'm an adult I just don't know where to set my goals. I wish I could talk to a doctor but my doctor is a jerk. :-/
  • bear_28
    bear_28 Posts: 59 Member
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    May I suggest getting a test instead? =)

    I recently had mine checked at a hospital. It was around $15 (I don't live in the US).
    The test showed my BMI, Body Fat, Visceral Fat (fat around the internal organs, I think), Body Fat and RMR. Oh, it also showed the body fat/muscle per body part (arms, leg, trunk and whole body).

    I think its a good investment. I had it checked because I'll be starting Insanity next week and I would like to know where I'm starting from. :flowerforyou:
  • Sunny_fit4life
    Sunny_fit4life Posts: 157 Member
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    May I suggest getting a test instead? =)

    I recently had mine checked at a hospital. It was around $15 (I don't live in the US).
    The test showed my BMI, Body Fat, Visceral Fat (fat around the internal organs, I think), Body Fat and RMR. Oh, it also showed the body fat/muscle per body part (arms, leg, trunk and whole body).

    I think its a good investment. I had it checked because I'll be starting Insanity next week and I would like to know where I'm starting from. :flowerforyou:

    That's a wonderful suggestion and I would LOVE to have that done. I may check into the cost, but I do live in the U.S. so... you seem to know what that means
  • CristinaL1983
    CristinaL1983 Posts: 1,119 Member
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    May I suggest getting a test instead? =)

    I recently had mine checked at a hospital. It was around $15 (I don't live in the US).
    The test showed my BMI, Body Fat, Visceral Fat (fat around the internal organs, I think), Body Fat and RMR. Oh, it also showed the body fat/muscle per body part (arms, leg, trunk and whole body).

    I think its a good investment. I had it checked because I'll be starting Insanity next week and I would like to know where I'm starting from. :flowerforyou:

    That's a wonderful suggestion and I would LOVE to have that done. I may check into the cost, but I do live in the U.S. so... you seem to know what that means

    I'm not sure what area you're in but for a BodPod it is usually $50. That would give a good idea of LBM and BF% plus I think it measures RMR.

    A Dexa scan is usually from $75-100 (you can get one done at some universities for a bit cheaper than other places) and will give you bone density, lean body mass, fat mass (I had this done)

    Hydrostatic weighing is done at some fitness centers and I have no idea about the cost.

    Checking at universities would probably be a good place to start (cost-wise). Some gyms and other fitness centers might have them as well but would probably be more expensive and may not have the same expertise in understanding the results.
  • Sunny_fit4life
    Sunny_fit4life Posts: 157 Member
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    Thanks. That's very helpful. I'm in a small town, though.... I guess I'll just have to look around.

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