As Kat related her experiences testing various scales and their estimations of body fat (you can read that post here), I wanted to do a comparison between a decent amount of collected data from my Renpho Smart Scale and a DEXA (Dual-Energy X-ray Absorptiometry) scan, and highlight some pros (always get a DEXA scan if you can) and cons (don't ever trust a body fat scale, as most take weight WAY too much into account), as well as my overall experiences.
A little bit about my background, I turned 41 this year, and have been working out since high school. Injuries (thanks to the military mostly) and surgeries (see injuries) have impacted my ability to workout continuously, but for the most part, I have been able to maintain a fairly regular workout schedule. Based off my own personal knowledge and research, I estimated that I was approximately 18-20% body fat. I’ve found in the past that some body fat scales can claim percentages as low as 5% or 10%, or some fairly low percentage, but single-digit percentages ordinarily take hardcore commitment to carb-depletion and dehydration, and are typically only achieved by bodybuilders, models, or actors for specific scenes on a very short-term basis. This piqued my interest in comparing how well my own scales were performing.
Renpho Smart Scale Data
One of the things that should almost immediately jump out with this data is that all of the "trends" are almost exactly the same. Muscle mass and bone mass measurements varied alongside fluctuations in body weight. If these measurements were truly accurate, bone mass should not change much, if at all, because that is one of the more "constants" that most individuals will have in regards to overall body composition.
Another thing is that, in the last two photos, is that while body weight can, and does, fluctuate day to day, and even hour to hour, an accurate body fat percentage should not. It is pretty much impossible for my body to go up nearly one full percentage point, and then back down, over the course of a few days.
DEXA Scan Up next are the results from my DEXA scan. There is a lot of data and information to process, but I will touch on the main aspects. According to the results of my DEXA scan, my actual body fat percentage is 17.8%. That is about what I expected it to be, despite Renpho saying 14.4 (ish). I was basing my estimate solely off of the visibility of abs, serratus, quads, etc. A percentage around 14.4 should have been showing more muscle definition than I was seeing.
My main take away from my DEXA scan results is that I am fairly close to overall symmetry, although my right leg has a bit more mass than my left (which is surprising, because of my injuries to my knee and hip and the long-term rehab/pain from those injuries). I also have a bit more android fat (fat on/around the central trunk region) than I'd like, and working on getting rid of some of that has been my main focus over the past few months.
The results are pretty much what I expected. I expected the Renpho scale to provide a decent data point, which it does, but I knew from previous experience that all of the home-grade scales take body weight WAY too much into the overall calculations. The main reason I did the DEXA scan was for an actual baseline, so I can compare these initial results to any future scans I have.
However, I will say that I may have finally found a home scale that actually overestimates bodyweight with regards to body fat (and rather than the opposite) with the Garmin Index S2 scale. The original Index was a good scale, but the S2 seems to overestimate my body fat percentage by roughly 5%. However, unlike the Renpho scale, the data is more constant, and more of an actual baseline. I will be writing up a review/comparison of the Index and S2 before too long, that will probably be my next project of collecting a month of data.
So, if you made it all the way through this post, congratulations! The main takeaway for me was that home scales will likely underestimate your actual body fat, base the overall data too much on weight, and also vary bone mass, which shouldn't change much at all.
Also, remember above where I mentioned that body weight can cause fluctuations, but body fat percentage cannot? During my discussion with the DEXA scan technician, I asked if they had ever actually done a test to see how much water one had to drink to get the body fat measurement to increase by 0.1%. The answer to my question was a very surprising gallon. Yes, you read that right. In order to try to get the DEXA scan to provide a different result, an individual had to consume a gallon of water to get the measurements to increase just slightly. The technician also noted the lowest body fat percentage they ever measured was just under 9%. This means that if you have a device that is recording a measurement that low, it’s very unlikely to be accurate.
In a world of exploding data points with regards to health and fitness, it is quite easy to find a "data source" that provides information that can enhance/enforce a bias that you may already have, instead of allowing you to establish the facts. I personally would much rather have data sources that have been proven to be accurate and reliable, and that will allow me to properly focus my workouts to help me achieve my goals. Hopefully this post, and those published by others on this forum and elsewhere, can help you to do the same.