Last week I told you how body fat testing is a prediction, not a measurement. I also talked about the 2-compartment model, its limitations, and how hydrostatic weighing is reasonably accurate for groups but can have an error rate of as high as 6% in individuals.
Hydrostatic weighing isn't the only 2-compartment model out there. Here I will discuss another 2-compartment model: the Bod Pod.
Bod Pod = Bad
The Bod Pod is based on similar principles to underwater weighing; thus you would think it would have similar error rates. In some instances, this is true; one study found error rates of about 2% on average, but errors of up to 6% in individuals. However, other research on the Bod Pod has shown error rates higher than underwater weighing; one study found an average difference of 5.3% between the Bod Pod and a 4-compartment model, and an error rate of up to 15% in individuals!
One of the reasons the Bod Pod is worse than underwater weighing is because there are more variables that can affect the results. For example, facial hair, body temperature, moisture, and the tightness of the spandex or swimsuit can all alter the results.
And, like underwater weighing, the Bod Pod can have errors when tracking changes over time. In fact, one study showed the Bod Pod to be very poor at tracking changes over time. Here's a chart from that study:
Changes in % body fat, comparing Bod Pod to a 4-compartment model
The X-axis of this chart shows the change in % body fat for the Bod Pod, while the Y-axis shows the change for the 4-compartment model. Each circle is an individual subject. You can see the big disparity between the two method. For example, one person gained 10% body fat but showed a loss of 1% with the Bod Pod. Another person lost nearly 10% bodyfat but showed only a loss of 1% with the Bod Pod. Another person lost about 5% body fat but showed a loss of 11% with the Bod Pod.
Do you see that "R squared = 0" statement in the chart? Do you also see the flat line in the chart? That means there was no relationship between changes observed with the 4-compartment model and changes observed with the Bod Pod. There was practically no agreement between the two methods. This means the Bod Pod is horrible at assessing changes within individuals over time. Now compare this chart to the one from last week on hydrostatic weighing. You can see that hydrostatic weighing did much better; even though there's some large error within certain people with hydrostatic weighing, there is at least reasonable agreement between hydrostatic weighing and a 4-compartment model in most people.
The Bod Pod: The Verdict
The Bod Pod does OK when looking at group averages, with some studies showing error rates of around 2%; however, other studies have indicated average error rates of over 5%. The individual error rate for the Bod Pod can be unacceptably high in some individuals, and the Bod Pod is horrible for tracking change over time. For these reasons I would recommend against using the Bod Pod as a body composition assessment tool. Hydrostatic weighing, despite some of its problems, is much more reliable.
Underwater weighing and the Bod Pod are not as widely available as other techniques, such as bioelectrical impedance (BIA) or skinfolds. Click here to read Part 4 of this series, where I discuss the accuracy, err, I mean inaccuracy, of BIA...
Let me be brief. Mr. Bishop seems to be quite ignorant on this matter and seems to let emotion instead of science lead him/her to conclusions. On the other hand, James seems to make a very sound argument. I applaud him for that. I know that it is only anecdotal evidence but my experience with the Bod Pod was great…..until I tracked by body fat changes over time. For the sake of time, the Bod Pod indicated that I had gained body fat % and lost 10 pounds (total weight lost) of lean mass over a 60 day period. That… Read more »
Thank you J!
It seems that the bodpod works great for runners but not people with muscle. This is like the old tests in the military that used to fail bodybuilders as being overweight. They were heavy but not fat. If I look like 10% but bodpod says 20+% then obviously there is a gap. I don’t have a belly or fat on any other part of my body so obviously it didn’t work.
Jeff, I had an experience very close to yours. The bod pod put me at 38.5%. A water test had me at 27% two years ago. The last two years I lost two inches off my waist, two inches off my hips, and one inche off my thighs. I looked the owner in the eye and asked her if I looked obese. She told me I didn’t have to pay because there had to be something wrong. Like you I exercise 5+ days a week. I run, lift weights, yoga, and hike every week. I wear a size 4/6. The… Read more »
I’m so relieved to read this post! I just paid $65 at the fancy East Bank Club, which has the only (so they say) bod pod in the city of Chicago. In the recent past I’ve done hydro testing and calipers w an elite trainer from Equinox – both came out to 14-15%. Bod pod has me at 28.1%, a few tenth a away from “dangerously obese.” The manager told me I was probably at serious tosh of health problems. I eat clean 90% of the week and workout 5 days a week, doing accelerated cardio strength training (HIIT plus… Read more »
I’ve been a competitive bodybuilder for over 20 years.. I’ve never bulked, I’ve always maintained a lean physique- I’m an Army spouse abc the Wellness center offers the bod pod- I’m 5’9 220lbs by this standard my BMI says I’m overweight. I did the bod pod it read my body fat at 21%– I did the test again the same result- so I started digging and contacted Kansas University which had one of the nations top Exercise Sciencd programs. I did the DEXA scan twice 10.4% body fat- a huge difference. To top it all off I just had completed… Read more »
Very interesting.I will keep this article in mind should things get wacky with my readings. Particularly since the article mentions that this inconsistencies when tracking changes. I have been taking advantage of a program at work that includes free BODPOD testing. So far is seems consistent with the weight loss that I have experienced but I’ve never really done any kind of body composition testing before so I do not have any point of reference. My initial results from March said that I was 34.4% at 220 lbs. My results today read that I am 30.6% at 208lbs. Since I… Read more »
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I did this and I think the results were very inaccurate. It came back at 33% BF. I train 1-2 times daily 6 days a week, my waist is 35, I weigh 210, and I’m 6′ tall. My workout partner is the same and looks that same as me. He was 19%. I ran 3 miles 3 hours prior to the test. I think that screwed this up.
I also survived Septic Shock with MOF 15 months ago. No sure if that did anything.
Bradley: The results are consistent, but have been shown to read high for those who are “fit”. My dexas showed 26.2% but the bodpod gave 28.9%. I would say the reading is 12-15% too high. Your actual BF is closer to 30%. Having said that, a 35in waist with 210lbs and 6′ frame, you are definitely higher than 25% BF. When I was DEXA 26% and BODPOD 28.9%, I was 33.5″ waist and 187lbs on 5’10” frame with decent muscle. You’re not supposed to do strenuous exercise or eat/drink significant amounts within three hours of the test. don’t blame the… Read more »
I know this is a late post but I had bod pod done this weekend and I was shocked at my analysis. I had hydro done 2 months ago and was 20% BF and this weekend I was 26%… All the while I cleaned my eating and I lift heavy 4-5 days a week and increased cardio by adding cycling and running 2-3 days a week. I have a cheat meal occasionally but not enough to see that huge of increase. Even worse my sister has same workout routine and we were tested at the same time. She had 20%… Read more »
Demetra. I had two different dexas and a bodpod done two months ago. The bodpod was almost 3% higher than the DEXAs (28.9% vs 26.2%) I had my first hydrostatic yesterday, it was 17.8% which I reckon to be approx 2.5% too low, as my actual BF at this point is closer to 20.5%. in two weeks time I will have a DEXA taken while I am on vacation in LA, and upon my return home, will have two different DEXAs taken on the same morning, and the bodpod redone within a day of the dexas. for fit indivuduals, the… Read more »
Excellent article!
The US Navy circumference method has been tested accurate to within +/-1% of hydrostatic. I use it with all of my clients after getting consistently absurd results from electrical impedance scales and gimmicks like BodPod.
There are several websites with free calculators. The formula uses age, height, weight, gender, and circumference of neck, waist, hips (women) to derive consistently accurate values. All you need is a tape measure and a scale.