Accuracy of home scale body fat%

moe5474
moe5474 Posts: 162
edited November 12 in Fitness and Exercise
I recently gained about 5 lbs but am puzzled as to why my body fat % dropped so much in the process. I started out at 141 with 20.1% body fat and am now just 4 short weeks later 146 with 15.1% body fat.

Could this even be possible? I know muscle weighs more than fat, but my clothes are all tighter, so I know I'm not getting smaller.

Replies

  • lizard053
    lizard053 Posts: 2,344 Member
    Accuracy? What's that? Mine doesn't give an accurate read AT ALL. I just use it to help me judge if I'm retaining water! It goes up when I'm retaining water, down when I'm not. But always around 41% . Yuck.
  • DocGu
    DocGu Posts: 51 Member
    I have found them to be only good for general trends. I use calipers to get a more accurate measure, the scale is always way off.
  • Chagama
    Chagama Posts: 543 Member
    I assume mine is not particularly accurate, but it is consistent, so as far as a trend it's useful.
  • Acg67
    Acg67 Posts: 12,142 Member
    BIA devices are among the worst at determining bodyfat. I'd look at any of the other methods that are out there

    Changes in body composition during weight loss in obese subjects in the NUGENOB study: comparison of bioelectrical impedance vs. dual-energy X-ray absorptiometry.

    Verdich C et al. Diabetes Metab. 2011 Jun;37(3):222-9.

    "RESULTS:

    At baseline, BIA significantly overestimated FFM and underestimated FM (by 1-3 kg on average) compared with DXA, and the limits of agreement were wide (mean ± 7-8.5 kg). "


    A comparison of dual energy X-ray absorptiometry and bioelectrical impedance analysis to measure total and segmental body composition in healthy young adults.

    Lehy S et al. Eur J Appl Physiol. 2011 May 26

    "BIA was found to underestimate the percentage total body fat in men and women (p < 0.001). This underestimate increased in men with >24.6% body fat and women with >32% body fat (p < 0.001). Fat tissue mass in the trunk segment was overestimated by 2.1 kg (p < 0.001) in men and underestimated by 0.4 kg (p < 0.001) in women. BIA was also found to underestimate the fat free mass in the appendages by 1.0 kg (p < 0.001) in men and 0.9 kg (p < 0.001) in women. Compared to dual energy X-ray absorptiometry, bioelectrical impedance analysis underestimates the total body fat mass and overestimates fat free mass in healthy young adults."

    and James Kreiger's excellent write up on bodyfat testing methods
    I’ve heard people make the argument that, while BIA may not be that accurate, it should work fine when tracking change over time. The theory, they say, is that the error should be the same each time you use it.

    The problem is that this isn’t true. As I mentioned in the article on hydrostatic weighing, the density and hydration of fat-free mass can change with weight loss. If this can affect the accuracy of hydrostatic weighing for measuring change over time, then you can be sure that the effect on BIA outcomes is going to be significantly larger.

    Researchers have looked at the accuracy of BIA for tracking body fat change over time. In one study, the disagreement between BIA and the 4-compartment model ranged from -3.6% to 4.8% for measuring change. This means you could lose 3.6% body fat, but BIA would show no change. Or, BIA could tell you that you lost 8.8% body fat when you really only lost 4%. In fact, in this study, plain ol’ bod mass index (BMI) did just as well as BIA for predicting change in body fat, except for in one person.
    BIA can be problematic because it’s a prediction based off of a prediction, so the error gets compounded. When you look at group averages for BIA measurements, there tends to be bias, with BIA often underpredicting how much fat you have. As with other techniques, the individual error rates can get high, with some research showing error rates of around 8-9%. In fact, BIA doesn’t do much better than BMI at predicting body fat in some cases. When it comes to measuring change over time, BIA can often underpredict the amount of fat loss, and the estimated change can be off by up to 8%.

    http://weightology.net/weightologyweekly/?page_id=146

    http://weightology.net/weightologyweekly/?page_id=162

    http://weightology.net/weightologyweekly/?page_id=175

    http://weightology.net/weightologyweekly/?page_id=218

    http://weightology.net/weightologyweekly/?page_id=283
  • sarafil
    sarafil Posts: 506 Member
    I'm not an expert, but I don't think it is very likely to lose that much body fat in 4 weeks, especially since you were at a very good percentage to begin with. 15% is getting close to just having enough body fat for survival, which isn't necessarily a great place to be at.
  • Tiggerrick
    Tiggerrick Posts: 1,078 Member
    Home body fat scale accuracy is all over the place... don't put too much stock into it. Make sure your scale is good at weights... the bells and whistles are often out of tune.
  • ilovedeadlifts
    ilovedeadlifts Posts: 2,923 Member
    Home body fat scale accuracy is all over the place... don't put too much stock into it.

    this.
  • shedoos
    shedoos Posts: 446 Member
    Absolutely horrible --

    I had a Bod Pod BF test completed and my scale is more than 5 percentage points off...
  • BeeSunny
    BeeSunny Posts: 172 Member
    Accuracy? What's that? Mine doesn't give an accurate read AT ALL. I just use it to help me judge if I'm retaining water! It goes up when I'm retaining water, down when I'm not. But always around 41% . Yuck.


    I agree I hate scales I measure!!
  • MJ7910
    MJ7910 Posts: 1,280 Member
    sounds like dexa scans are the most accurate, followed by bod pod?
  • Sublog
    Sublog Posts: 1,296 Member
    All methods of measuring body fat have issues - including Dexa and Bod pod.

    "body fat “measurement” is not a measurement at all. Body fat testing is a prediction, and a very poor one."

    This:

    http://weightology.net/weightologyweekly/?page_id=146

    And this:
    http://www.bodyrecomposition.com/fat-loss/problems-with-measuring-body-composition.html
  • katiew00t
    katiew00t Posts: 164
    well *kitten*. good thing I only paid $30 for my "fancy" scale.
  • moe5474
    moe5474 Posts: 162
    Hhhhmmm That's what I thought. I knew it was near impossible for me to lose that much body fat that fast, especially when I had begun eating poorly and had put on a few pounds :)
  • AZackery
    AZackery Posts: 2,035 Member
    I recently gained about 5 lbs but am puzzled as to why my body fat % dropped so much in the process. I started out at 141 with 20.1% body fat and am now just 4 short weeks later 146 with 15.1% body fat.

    Could this even be possible? I know muscle weighs more than fat, but my clothes are all tighter, so I know I'm not getting smaller.

    Are you the only person that uses your scale? Do you think that you could have mistakenly chosen a wrong option? I don't know about you, but for my scale, I have to confirm my settings. One day, I didn't realize that I have clicked the button and chosen kg, instead of lb and when I've stepped on the scale, I was like my weight can't be right and when I've noticed the kg next to the weight, I've noticed that I've made a mistake. It's easy to make a mistake, while confirming your status to click on the button that determines what gender you are. If you've made a mistake and and chosen the male's gender, then your body fat percentage would have been lower.

    I suggest you make sure your settings are right and step on the scale again today, just to see if your scale will give you the same body fat percentage reading.

    Nothing is 100% accurate, except for an autopsy and no one will know their true body fat percentage then.
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