Body Fat Percentage Scales

jemhh

Zedeff wrote: »

All of the posts saying "they aren't accurate" are missing the point. They don't need to be accurate. They need to be precise. Body fat measurement by bioimpedence, presuming you maintain relatively consistent conditions (similar levels of hydration at each measure) are quite precise.

They are excellent for charting progress over time, they are bad for spot measurements. I highly recommend my Omron scale which has both hand and feet sensors for body fat measurement.

Except this isn't true. Read the article that Hornsby posted below.

Hornsby wrote: »

No. They are a joke and a waste of money. They aren't accurate and aren't really good for even guessing trends either. Here is a good synopsis IMO.

http://weightology.net/weightologyweekly/index.php/free-content/free-content/volume-1-issue-4-the-pitfalls-of-body-fat-measurement-parts-3-and-4-bod-pod-and-bioelectrical-impedance-bia/the-pitfalls-of-bodyfat-measurement-part-4-bioelectrical-impedance-bia/

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.

And, as I posted before, there is no way my own BIA has been close to reflecting the change in my BF% over the past two years.

Zedeff

Respectfully, your anecdote is not a good form of evidence and is more likely related to user error than the device being off. These are well studied devices. Here are the first few papers that came up using Google Scholar, a much better free resource than some random website (Weightology).

The American Journal of Clinical Nutrition says bioimpedance scales are "sufficiently precise for use in clinical research."
http://ajcn.nutrition.org/content/64/3/489S.short

Another paper in the same journal notes that no difference was found in bioimpedance measures of body fat percent during multiple phases of the menstrual cycle.
http://ajcn.nutrition.org/content/50/5/903.short

The International Journal of Obesity estimates that bioimpedance scales have precision rates of 1.1% on same-day remeasurements, and double that for between day measurements - pretty damn good.
https://www.researchgate.net/profile/Niels_Kolthoff/publication/12743973_Validation_of_a_leg-to-leg_bioimpedance_analysis_system_in_assessing_body_composition_in_postmenopausal_women/links/55fe7bd308aeafc8ac7c5d21.pdf

The International Journal of Body Composition assessed bioimpedance precision (in rats and not people, but it's the same technology) and found its precision to be 1.5% for assessing fat mass.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2722071/

The European Journal of Clinical Nutrition also published on this question, and found that same-day retesting had a <1% variation, and multi-day retesting had a 1.7% variation when using a combined hand-foot electrode setup as many modern scales offer.
http://www.nature.com/ejcn/journal/v58/n11/abs/1601993a.html

trigden1991

Wake up and measure your bodyfat using one of these scales. Now drink a litre of water and repeat. Congratulations your lean mass has increased and your bodyfat % has decreased. There is a vast amount of error in these, especially among obese and very lean people.

Zedeff

trigden1991 wrote: »

Wake up and measure your bodyfat using one of these scales. Now drink a litre of water and repeat. Congratulations your lean mass has increased and your bodyfat % has decreased. There is a vast amount of error in these, especially among obese and very lean people.

This is user error, not device error.

rcktgirl05

I came to this post because I'm confused about these scales and calculators and I was searching for posts about bioimoedance. The calculator link in an earlier response says I'm 27% bf, my Omron handheld says I'm 34% bf while my FitBit Aria scale says I'm 44% bf. See why I'm confused? I'm more likely to trust the Bioimpedance method than the calculated method (no scientific reason just a feeling) but I am surprised to see such a huge difference in the two similar methods. Short of paying for a DEXA scan, how do I know? I know I should just go for trending overall but the health difference between 34 and 44% is pretty significant.

AnvilHead

Read the Weightology link. It explains in detail why BIA is neither accurate nor precise.

rcktgirl05

AnvilHead wrote: »

Read the Weightology link. It explains in detail why BIA is neither accurate nor precise.

Thanks for recommending that. It makes sense to me now why the two BIA methods are wildy different. I am disproportional between my upper and lower body (by at least 2 clothing sizes) so the fact that the handheld estimates a much lower amount of fat as it goes through my upper body as opposed to the Fitbit scale likely only going through my lower body really does seem to explain it. I'm satisfied with just knowing this alone, and I don't need an absolute answer. I'll keep trending but at least I understand!

trigden1991

Zedeff wrote: »

trigden1991 wrote: »

Wake up and measure your bodyfat using one of these scales. Now drink a litre of water and repeat. Congratulations your lean mass has increased and your bodyfat % has decreased. There is a vast amount of error in these, especially among obese and very lean people.

This is user error, not device error.

How is this user error? It is a method to show that hydration levels greatly affect your scale weight.