I haven’t gotten my bodyfat measured in a long time. In the past, I have done it with caliper tests, but there are a lot of new methods on the markets now. My gym has an Omron HBF 306C hand-held body fat analyzer and I decided it was time for a check. I was shocked to see how my body fat ratio had shot up over the years, and I naturally held onto the hope that these new devices were simply highly inaccurate. Sadly, that’s not the case – I’ve just put on that much fat!
How do you measure body fat?
There are many different ways to measure your percentage body fat. The only truly accurate way is to do chemical analysis on a cadaver, but that’s damn inconvenient for most of us. For many years, the “gold standard” was hydrostatic body fat testing by immersion (that is, weighing under water), but that has mostly given way to Dual-energy X-ray absorptiometry (DEXA). These are more convenient than having chemical analyses done on our dead bodies, but for most of us, these are out of reach.
Traditionally, those of us without access to such testing facilities have used calipers to get skinfold measurements and calculate the percentage body fat from there. Usually you measure the thickness folds of skin at several different locations on the body and use a formula to calculate the percentage body fat. Calipers, however, tend to be subject to a lot of error due to the technique of the person taking the measurement, and also tend to be less accurate at the extremes. In particular, the caliper method does not measure intramuscular fat, only subcutaneous fat. Bodybuilders, who tend to retain intramuscular fat, may check in at 3% with calipers, but may test out to 12% to 18% body fat with hydrostatic weighing. Other athletes who do more aerobically and burn more intramuscular fat might get fairly accurate results from calipers.
Enter Bioelectrical Impedance Analysis (BIA)
In more recent years, a variety of devices have come out that send a tiny amount of current through your body and measure how much resistance there is. Since the resistance of fat and muscle are different, in theory they can calculate the percentage of body fat based on this. These tools are cheap (under $40 for a nice one), widely available and relatively easy to use. The Omron HBF 306C at the gym is one of these and it’s what I used.
There is another class of analyzers that use Near-Infrared Interactance (NIA), but these are more likely to be professional tools.
Is the Omron HBF 306C (and similar body fat analyzers) accurate?
In a word, yes, but with caveats and those caveats may effect a significant number of people. A group of researchers compared different toolls across a broad spectrum of people, varying in age and gender, measuring body fat. They got baseline numbers using DEXA for adults and hydrostatic immersion for children. In generally, they found that the BIA tools tended to slightly underestimate body fat, but were generally quite accurate (within 2%).
They tested the
- Omron HBF 360 (BIA) – I believe that despite the higher number, this is the predecessor to the HBF 306C at the gym
- InBody 320 Body Composition Analyzer (BIA)
- Futrex Bod-eComm system (NIA)
The researchers found that all three “tend to underestimate %BF in both men and women.” That said, they also report that “BIA tends to overestimate the %BF when subjects are relatively lean and underestimate %BF when subjects are obese.” These divergences vary with population and device.
- The Omron body fat analyzer tends to have the most accuracy problems in men and women aged 18-35.
- InBody had the biggest errors in males aged 36-50.
- Bod-eComm tends to be inaccurate for women aged 51 and older.
There is one big problem with the study, however. They say specifically: “Food intake and hydration status were not monitored as part of the study.” The problem with this is that BIA analyzers are sensitive to fluid levels in the body and can’t be used for a period of time after eating, drinking, bathing or exercising. I’ve tested this for myself. For example, I dropped from 16% to 12% after a weight training session. Obviously, I didn’t lose several pounds of fat in one session!
So one manufacturer , who is trying to sell the convenience of NIA testing, says that a truly accurate test with a BIA device requires
- fasting for at least 4 hours before testing, especially avoiding caffeinated products; also must avoid alcohol for 48 hours prior.
- avoid exercise for 12 hours before
- Must have urinated within 30 minutes of the test
Omron only requires 2 hours without eating, drinking or exercising. Still, they do require this, and one wonders if the researchers might have found the devices more accurate.
The Next Generation in BIA: Omron HBF-510W Full Body Composition Monitor with Scale
I haven’t seen any tests of this one yet, but I’m putting it on my Amazon wishlist. Most BIA bodyfat analyzers only measure impedance from foot to foot or arm to arm, meaning they don’t even pass through the parts of our bodies that hold the most fat. The Omron HBF-510W measures from hand to foot and hand to foot with two hand sensors and four foot sensors. In theory (and according to Omron), this makes it far more accurate than the foot-only or hand-only devices. I don’t think there are any independent tests published in the peer-reviewed literature, but assuming they got the software right, it stands to reason it would be more accurate (and it doubles as a scale). It’s a bit more expensive, but at $60 it’s still quite affordable and cheaper than buying a separate handheld device and scale. So even though I haven’t seen scholarly literature on this unit, if I were looking for good accuracy at a reasonable price, I would buy the Omron HBF-510W Full Body Composition Monitor with Scale (and stay tuned, because I think I just might!)
For the last few years, I’ve actually been using a Taylor bodyfat scale that I got for $35 at Bed, Bath and Beyond. I’ve found it to be fairly far off in terms of actual percentage bodyfat, but directionally correct. Meaning that if I eat a bunch of ice cream and look in the mirror and think, “Hmm… I’m kinda chubby,” my scale instantly corroborates that fact by increasing my percentage bodyfat. I don’t care about the actual number as long as it is roughly correct from day to day and it seems to be.
There are a few caveats though:
- If you do a lot of exercise and get really dehydrated, it will throw it off.
- You need to follow all the advice above — pee before you hop on the scale and do not eat or exercise beforehand. Essentially, get out of bed, pee, then hop on the scale and it will be very consistent, barring dehydration.
- Don’t move the scale. My floor is uneven and if I move the scale, that throws things off.
My scale is nothing special and appears to be unavailable, but it is roughly like this one. That’s currently only $16 with free delivery via Prime and has the same feature set as mine, but again, you could walk into any store that carries scales and get one these days. Just don’t expect the bodyfat number to be accurate. If you are looking to track progress, it’s great. If you are looking to brag about your low bodyfat, then you need to go get a DEXA scan.
In any case, my conclusion is that tested properly, with adequate fasting and rest, it’s close enough to label me as kind of fat (15% currently). I suspect that my caliper measurements were likely always a bit low and based on the research, I would expect my BIA measurements to be a bit high. Still, it’s motivating me to hit the gym.
- Nicole E. Jensky-Squires, et alia, “Validity and reliability of body composition analysers in children and adults,” British Journal of Nutrition, vol 100 (2008), pp. 859–865. All quotes and citations from this article unless otherwise noted.