Today at work, the nurse was in the cafeteria with a salesman-type offering free body fat measurements using a gadget that looked like this.
I went up for a measurement (21.5% when I gave rough estimates of hight/weight, 19% when I gave “favorable” estimates). It was quite simple – she keyed in my numbers and had me hold the device at arm’s length for about ten seconds.
I asked them how accurate it was: they both claimed it was more accurate than caliper measurement. I asked how it worked and the salesman fellow told me that it sends a low energy current through your body to make its measurements.
Now for my questions:
How accurate are these things really? I’m sure the salesman was being optimistic (just as I was when I said 205 lbs even though I only reach that weight after a four mile run :)), and I’m sure that the nurse was just repeating what he had told her.
How do they work? I can’t imagine that the resistence of my sweaty grip was the same for my two measurements – doesn’t that affect anything?
It seems too good to be true, especially after looking at a site like this that makes it appear that one needs extremely expensive equipment or a highly trained caliper user to get good measurements.
Actually, the caliper is highly dependent upon it’s operator – and there are mechanical limitations to calipers. I cannot be measured with a standard caliper. I’m too large.
There is a simple device that beats the caliper. It is the gold standard for body fat measurement. That device is a displacement tank. For such a simple device, they are awfully hard to find. I was measured at the Naval Health Research Laboratory, Detachment RTC, in San Diego. I think that one was dismantled or moved some 20 years ago. At the time, it was the only tank the military had access to in the region.
I have a Danita scale that measures body fat the same way, by sending a small electrical current through the body; you only have to program it with your height. I don’t know how accurate it is, but at least it’s consistent, and since I stand on it, I don’t have the variable grip problem. I’d be skeptical, though, about a device you have to grip - my exercise bike supposedly measures my pulse when I grip the handlebars, but the numbers are anything but accurate.
You should also know that these body-fat devices should not be used by anyone with a pacemaker.
I bow before the experts at Testosterone Magazine. Clearly an unimpeachable source.
Sorry, that was a little snarky. The article was very good. However, IIRC, one reason that tank was at the Naval Health Research Laboratory was a long-term study of body fat variation of healthy volunteers (active-duty sailors of age 18-45). Several thousands were measured with multiple methodologies. Whatever the ‘actual’ body fat vs. the hydrostatic method, the hydrostatic method proved reliable and reproducible, and optimally capable of tracking variations due to exercise and activity. Of course, this was a controlled study conducted by health scientists.
I agree that appropriate calipers operated correctly are probably the best method available to the general public. However, a displacement tank was likely used as the reference standard for the caliper’s design and calibration.
Well, although the Tanita scales and the like are inaccurate, and highly confounded with hydration, the readings they produce are very repeatable. It’s also quite simple to take BF measurements at the same time of day, which alleviates some of the confounding factors. The hydration problem is also fairly easy to keep track of - when using my scales, any large changes in BF% were usually easily tracked to a recent long run or suchlike. I think they are a useful tool, but accurate? No. Precise? With certain limitations, yes.
If you parlez Spanish, then Moreno et al [2001, Rev Esp Salud Publica 75: 221-236] have a paper comparing the BF% results obtained from skinfold measurements (SF), bioelectric impedance (BIA - i.e. Tanita scales and the like) and biodata (i.e., anthropometric measures). I no parlez Spanish, but the abstract suggests that BIA is a worthwhile method, where the results correlate highly with those obtained from SF.
I’ve invented a gadget for accurately measuring body fat. The accuracy is unmatched. Unfortunately, it involves throwing you in a blender and centrifuging the results.
Not that many people have access to it, but dual X-ray absorbance is what the USDA uses to measure body fat in the research studies that I’ve participated in.
The researchers claim it’s much more accurate than water tanks and they’re in the business of studying body composition.
I just saw a summary in ‘The Week’ that researchers in Great Britian have developed a scanner that uses radio waves to calculate body composition; this would have an advantage over X-rays when it comes to repeated measurements. The original article is in ‘New Scientist’.
Still, the average person is out of luck when it comes to access to water tanks, X-Ray or Radio scanners.
But from the Testosterone Magazine page:
[after dissection] The next best option is to get into a research study that uses a multi-compartment model, which combines measurements of body density from hydrostatic weighing, total body bone mineral from dual energy x-ray absorpitometry, and total body water from deuterium oxide dilution. I can assure you that it’s not very likely and also not very practical. Sure, you get an accurate measure of your body composition, but what are you going to do next time?
Me?: volunteer for the next heavy water study the USDA runs
I live close by and they pay you (now if they only get that radio wave scanner–I don’t want to be exposed to X-Rays more than I have to be).
