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Measuring body fat percentage?


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How do those of you who measure your body fat do so? I have one of those scales that reads out body fat percentages, but I'm quite sure it's a completely useless device for measuring anything other than weight. As I said in my blog this morning:

 

My scale says I'm at 25.3% body fat. Although that's probably not very far off (I'd say it's a tad high judging from looking at pictures of men who say they're x% body fat), I have to say that at least this brand of scale (Homedics) is completely useless for accurately measuring body fat. If I exercise and sweat a lot, it registers my body fat percentage as dramatically lower, by exactly the amount you'd expect if I'd lost all that weight as fat instead of the majority of it being water (sweat). And this morning I measured my body fat a second time, after I'd had two bananas and a cup of tea for breakfast. Now it says I'm at 25.9% body fat! Yeah, I have sugar in my tea, but there's no way I gained a pound of fat in two hours from consuming around 300 calories!
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According to the US Navy formula (available in calculator format at http://lowcarbdiets.about.com/library/blbodyfatcalculator.htm), I'm at about 18.7% body fat. That seems a little closer to the mark than the 25.3% I got this morning on my bathroom scales. I mean, of course it's self-serving to pick the lower figure, but given that no one would notice I have any belly fat at all unless I have my shirt off, 25.3% just seems less plausible. (I'm just shy of 5'7", 165 lb., and my waist currently measures just under 34 inches.)

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According to the US Navy formula (available in calculator format at http://lowcarbdiets.about.com/library/blbodyfatcalculator.htm), I'm at about 19.7% body fat. That seems a little closer to the mark than the 25.3% I got this morning on my bathroom scales. I mean, of course it's self-serving to pick the lower figure, but given that no one would notice I have any belly fat at all unless I have my shirt off, 25.3% just seems less plausible. (I'm just shy of 5'7", 165 lb., and my waist currently measures just under 34 inches.)

 

 

Thanks for the link, according to that I'm at 16.3% body fat still after cutting from 172 to 154 (my first serious cut). If that's anywhere near accurate, it looks like I'm shooting for about 10% BF before I begin gaining.

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According to the US Navy formula (available in calculator format at http://lowcarbdiets.about.com/library/blbodyfatcalculator.htm), I'm at about 18.7% body fat. That seems a little closer to the mark than the 25.3% I got this morning on my bathroom scales. I mean, of course it's self-serving to pick the lower figure, but given that no one would notice I have any belly fat at all unless I have my shirt off, 25.3% just seems less plausible. (I'm just shy of 5'7", 165 lb., and my waist currently measures just under 34 inches.)

 

 

Thanks for the link, according to that I'm at 16.3% body fat still after cutting from 172 to 154 (my first serious cut). If that's anywhere near accurate, it looks like I'm shooting for about 10% BF before I begin gaining.

 

It's gotta be more accurate than my bathroom scale. I weighed about 7 pounds more when I took the picture in my current avatar, and if I saw me at that weight on the street there's no way I'd think "that guy has about 28% body fat" or whatever it said then. That said, I'd think taking only the person's sex and 3 other pieces of information (height, neck size, and waist size--there's also hip size for females), as the Navy formula does, wouldn't yield a very precise figure, either.

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Some of the scales use an electric pulse to measure body fat. I have heard those are accurate within a couple percent. The scale you have sounds like it only takes BMI into account, something entirely useless for an active individual. BMI charts assume I am 24-25% body fat, but I am actually right around 10%.

 

I believe hydrostatic weighing is the only "completely" accurate way. It is probably really expensive and you need to find somewhere that does it, though.

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Some of the scales use an electric pulse to measure body fat. I have heard those are accurate within a couple percent. The scale you have sounds like it only takes BMI into account, something entirely useless for an active individual. BMI charts assume I am 24-25% body fat, but I am actually right around 10%.

 

I believe hydrostatic weighing is the only "completely" accurate way. It is probably really expensive and you need to find somewhere that does it, though.

Even that has a slight error percentage. Calipers are much too error prone, and even the smallest reading can throw off your body fat quite a bit. The BMI charts become useless wants you put on the slightest amount of muscle. Honestly, the hydrostatic body fat is completely pointless. If your at a point where you need to accurately calculate your body fat, it probably won't tell you any useful information. If you want to be more cut, there are ways to do it, but telling you that you have a 15% body fat instead of a 11% won't change anything about the diet.

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Some of the scales use an electric pulse to measure body fat. I have heard those are accurate within a couple percent. The scale you have sounds like it only takes BMI into account, something entirely useless for an active individual. BMI charts assume I am 24-25% body fat, but I am actually right around 10%.

 

I believe hydrostatic weighing is the only "completely" accurate way. It is probably really expensive and you need to find somewhere that does it, though.

 

As far as I know all of the scales that give body fat percentage readouts pass an electric current up one leg, and it goes through part of the abdomen and down the other leg. From what I've heard, they are accurate within about 4% of the correct body fat percentage, if used under the correct conditions. Underwater weighing apparently has an error of a couple of percent and a technique using X-rays is even more accurate. Estimates using skinfold measurements with calipers probably fall in between scales and the more sophisticated techiques in accuracy, if they're done accurately by someone experienced in the technique. Estimates using body circumference measures (waist, neck, height, etc.) such as the Navy technique are thought to be less accurate than correctly done skinfold measurements--generally they just rely on two or three measurements, so they don't fully take into account people's different body proportions.

 

There are a number of reasons why body fat scales are less accurate than some of the other techniques. Of course there are reliability problems because for them to give consistent readings you have to be at exactly the same place in terms of hydration, amount of food in your stomach, amount of moisture on your feet or other parts of your body when you're standing on the scales (wet feet and dry rest of body is the way you're supposed to do it), etc., and it's hard to be that consistent. As far as their validity, a problem is that the current doesn't pass through the entire body, it just goes up one leg and down the other because that's the quickest route out of the body. The principle behind the technique is that muscle conducts electricity better than fat because it contains more water. But since the current doesn't go through the entire body, people with the same body fat percentage but different distributions of fat are going to have very different readings, given that the calculations are done from the same formula. There are different formulas used for men and women, of course, but obviously individual men and women can have pretty different fat distributions. In my case, I store more body fat in my butt and inner thighs than I think the average man does. I've also, judging from my increases in strength and from looking in the mirror, put on perhaps a couple of pounds of muscle in my upper body over the last few months. So that's why I think the reading it gives for me (24.9% this morning, at 163.6 pounds) is probably a little high.

 

You can set my scales to an "athletic" setting that uses a formula that's supposed to take into account that people who work out have more heavily muscled upper bodies. But when I do that, it reads out around 11%, and I know that's far too low because if I were at 11% I'd have a totally flat stomach, etc. A one-size-fits-all formula can't differentiate between people with the upper body muscles of a football player or experienced bodybuilder and someone who's merely been working out steadily for a few months.

 

Of course, what we're doing this for is not to achieve some percentage of body fat, but to improve our level of fitness and strength and the appearance of our bodies! As long as I'm going in the right direction, I'm not going to obsess over what my exact percentage of body fat is (any more than I already have!). But it's interesting to compare the appearance of people with different reported percentages of body fat. Google around and you can find a ton of pages with such pix; here's one: http://forums.johnstonefitness.com/showthread.php?t=31392. If the body fat percentages people are reporting on this page are anywhere near accurate, then I'd say my body fat right now is somewhere in the low 20s.

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I can't imagine that navy calculator is anywhere near accurate. I have one of those scales that measure impedance, its numbers are inline with what the calipers tell me, but it seems to be easily thrown off by towel-dry moist skin. I've noticed that according to it I lose about 2 lbs of fat during ~10 minutes of showering. I'm not usually that dirty... or active in the shower.

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The body fat measuring function on those home scales really only measures the amount of water in your lower legs, then based on how easy the current flows, factoring your height/weight/sex/activity level it makes an estimate of how much body fat you have. They are highly inaccurate under most conditions.

 

My scale would read anywhere from 12 to 18 percent body fat on a day to day basis... I knew I was much lower than that. My guess was around 6%. I was measured by a professional at 4.5% bf.

 

From what I have read, Dexa scanners are the most accurate and consistent when it comes to measuring body fat.

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