Converting BMI to body fat %... Can it be done?

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10668

Tacoma, Washington

Subject: RE: Converting BMI to body fat %... Can it be done?

Can't be done. BMI makes no distinction between fat or lean mass.

For example, a few years ago I did a survey on the testosterone.net forum, and almost to a one they all came out obese or borderline, and yet they all sported body fat in the 10% and less (some WAY less) range.

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Champion

16151

Checkin' out the podium girls

Subject: RE: Converting BMI to body fat %... Can it be done?

I'm "obese" with a BMI of 30.6. I go 240lbs and am 6' 3". But, my body fat is 15% and into the Fit to athletic categories. I'm pretty muscular and yes, could drop 20lbs easily to improve my physical health. But I'm not "obese".

BTW: Went looking after you posed the question. This page has 1 calculator for BMI-BF percentages from the US military. Mine calculates to 12.6% vs the 15% I get from my bathroom scale or 14% from skinfold calipers. Good ballpark estimation.

http://en.wikipedia.org/wiki/Body_fat_percentage

Some caveats: Hydration can change this measurement, bathroom habits can change it, time of day can change it. Be consistient about those if you want the data to mean anything.

The trick to BF is that hydrostatic weighing is the best method to get an absolute value. But, if you use the same method and track trends, that is reliable since you're introducing the same method and the error should be reproduceable measurement to measurement.

Edited by pitt83 2008-08-13 7:50 AM

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Expert

938

Subject: RE: Converting BMI to body fat %... Can it be done?

briderdt - 2008-08-12 11:29 PM

Can't be done. BMI makes no distinction between fat or lean mass.

For example, a few years ago I did a survey on the testosterone.net forum, and almost to a one they all came out obese or borderline, and yet they all sported body fat in the 10% and less (some WAY less) range.

I'd agree. Speaking as someone who has gone from morbidly obese to simply overweight according to BMI, I can tell you BMI at the lower levels is a crock. I still need to lose some weight, but being 5'9" I don't see how 165 pounds (minimum weight for BMI normal weight) for me would be healthy. However, not to sound sexist, but I could see a 5'9" woman at 165 (since BMI makes no distinction for sex either) being healthy and normal. In any regard, I believe BMI is given too much credit by some. If anything, I've learned through my weight-loss journey, it's this: you know when you are at a healthy weight, when you are honest with what you want to achieve.

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Pro

6767

the Alabama part of Pennsylvania

Subject: RE: Converting BMI to body fat %... Can it be done?

I wouldn't get too stressed about a BMI. It's not a very useful number, but really seen best as a shorthand. Most Americans are overweight/obese. Therefore for most of them, BMI is a good shorthand for how much overweight they are. But people with high muscle mass will have inflated BMI numbers. Better is the waist measurement, or a waist to hip ratio.

Risks associated with obesity increase with a waist >35 inches for women, >40 inches for men. Waist to hip should be <1. Ideally for women, 0.8 and for men 0.9.

If the concern is being underweight, for women, there is a nice biological marker: menses. Loss of periods is highly correlated with having enough body fat to maintain hormone levels.It used to be thought to be a side effect of exercise in general, but the data points more to body composition overall.

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Extreme Veteran

552

Minnetonka, MN

Subject: RE: Converting BMI to body fat %... Can it be done?

No.

BMI cannot be converted to body fat %.

Member

360

Denver, CO

Subject: RE: Converting BMI to body fat %... Can it be done?

kagoscuba - 2008-08-13 7:41 AM

briderdt - 2008-08-12 11:29 PM

Can't be done. BMI makes no distinction between fat or lean mass.

For example, a few years ago I did a survey on the testosterone.net forum, and almost to a one they all came out obese or borderline, and yet they all sported body fat in the 10% and less (some WAY less) range.

I'd agree. Speaking as someone who has gone from morbidly obese to simply overweight according to BMI, I can tell you BMI at the lower levels is a crock. I still need to lose some weight, but being 5'9" I don't see how 165 pounds (minimum weight for BMI normal weight) for me would be healthy. However, not to sound sexist, but I could see a 5'9" woman at 165 (since BMI makes no distinction for sex either) being healthy and normal. In any regard, I believe BMI is given too much credit by some. If anything, I've learned through my weight-loss journey, it's this: you know when you are at a healthy weight, when you are honest with what you want to achieve.

Not to rain on your parade but I'm a 5'11" guy at 155 lbs - I'm in the middle of the "normal" range and I'm pretty sure I'm healthy. I don't think someone is unhealthy if their BMI is in the "normal" range - even if the person is male.

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938

Subject: RE: Converting BMI to body fat %... Can it be done?

csibona - 2008-08-13 4:09 PM

kagoscuba - 2008-08-13 7:41 AM

briderdt - 2008-08-12 11:29 PM

Can't be done. BMI makes no distinction between fat or lean mass.

For example, a few years ago I did a survey on the testosterone.net forum, and almost to a one they all came out obese or borderline, and yet they all sported body fat in the 10% and less (some WAY less) range.

I'd agree. Speaking as someone who has gone from morbidly obese to simply overweight according to BMI, I can tell you BMI at the lower levels is a crock. I still need to lose some weight, but being 5'9" I don't see how 165 pounds (minimum weight for BMI normal weight) for me would be healthy. However, not to sound sexist, but I could see a 5'9" woman at 165 (since BMI makes no distinction for sex either) being healthy and normal. In any regard, I believe BMI is given too much credit by some. If anything, I've learned through my weight-loss journey, it's this: you know when you are at a healthy weight, when you are honest with what you want to achieve.

Not to rain on your parade but I'm a 5'11" guy at 155 lbs - I'm in the middle of the "normal" range and I'm pretty sure I'm healthy. I don't think someone is unhealthy if their BMI is in the "normal" range - even if the person is male.

Sorry...I did not mean that to mean everyone, which is why I qualified it with "for me." I've been a weightlifter for years, so my body-type is different. Although I may get closer to 165 than I think, since my tri-coach recently has cut my weightlifting by 50%.

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Resident Curmudgeon

25290

The Road Back

Gold member

Subject: RE: Converting BMI to body fat %... Can it be done?

SmBkRn450 - 2008-08-12 10:25 PM Hey... So I went to the doctor today, they told me my BMI, but not my body fat %... Anyone know how (or if...) you can convert your BMI to BF%?

Not sure what thread to have put this under, so don't be hatin' on me. :]

Meant as a nothing but compliment, but from your avatar I would say BMI & BF% should be of no concern to you!

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Converting BMI to body fat %... Can it be done?

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