Home bodyfat scales: do they really work?

[Yep.]

I posted some of my photos over at the pictures forum earlier today and asked that users try to estimate my bf%. I did this because a trainer at my gym took skinfolds last year and told me that I was just over 8%, but my girlfriend's bodyfat scale (the one made by Tanita that you stand on barefoot) tells me I'm 14%. The problem is that my friend was skinfolded last week at 16% and the scale told him he was 16%. Does anyone have any experience with these scales? Are they accurate? Do they differ from person to person?

For reference the link the the photos:

http://forum.bodybuilding.com/showthread.php?t=471382

[magnumfreak]

They work by measuring body resistance. Unfortunately this can vary tremendously from person to person. How damp your feet are, whether you have calouses or not, how much water you drink, all have an effect on the reading. I have one at home and I have seen it vary 5 percent in just a few hours. I don't think my BF changed that much.

[Bradentothemax]

I have seen these in stores and was very leniant so decided not to buy one. Wouldn't it be the most accurate to just weight yourself when you first wake-up?

[Yep.]

Braden, morning is probably the best time to weigh yourself, but as for measuring bf% on a home scale, there's probably no good time. I think magnum is right on the money when he says that resistance varies greatly from person to person. The callouses/ damp feet point makes perfect sense. It seems completely pointless for a company to manufacture a product that people tend to count on, and have it be so blatantly inaccurate.

[sharaabi]

ive read a ton of reviews before i returned my scale, 88/100 people are NOT satisfied with it.

[DJohnson]

I only check my BF in the morning with the BF scale and I also have a accumeasure. Obviously one of them is wrong because the accumeasure puts me at 20% and the scale puts me at 27%, but so far the scale has definately shown whenever my BF percentage goes down. I saw my BF percentage slowly drop with both the accumeasure and the scale.

So if anything, you can probably use the scale to see if you're gaining or losing BF. Other than that, I wouldn't count on it for accurate results.

[Yep.]

I just had a look at Tanita's website... apparently they're manufacturing fat scales that measure body water % along with bf% and give a reading for both. Meybe they realized how off their bf% measurements were. Body water seriously throws the bf measurement off, as water and fat resist electricity to a greater extent than does lean muscle.

[aaronk]

What about that BF% measure that you hold in your hands? I think its in the BB.com store.

[magnumfreak]

They are just as bad. Not only will they vary for the same reasons the scale ones do, how hard you grip it will effect the readings on the hand held ones. I had fun with one of those at a "health fair" one day. Grabbed it normal got one reading, gripped it hard got another, barely held it and got another totally different reading. They are not worth it in my opinion.

[nreeldeep]

there's no way a scale can measure your body fat just by standing on it. all a scale can measure is your weight. i'm amazed that people fall for this. Just thinking about it for 5 minutes should make you roll your eyes at the entire idea.

[nreeldeep]

invest in a full length mirror.

[nreeldeep]

if there's fat you will certainly see it. then curtail your diet and workout regiman to get rid of it. look in the mirror periodically to chart your progress.

[TurboGuy]

Some things to keep in mind:

1) Whether skinfold testing or bioelectrical impedance analysis (BIA) testing (ie. BF scales) your error is plus or minus 3-4%. Not 3-4% of your result, but add or subtract 3-4 to your actual result. That is signficant. This is the accuracy of the the method though, not the REPEATABILITY.

2) These methods should be used primarily for tracking changes, not ABSOLUTES. One guys' acutal may be 10%, but his scale is telling hime 14%, and the next guy could be 14% but the scale (or caliper) could be telling hime 11%. This key to these tools is the track changes. BIA can be very repeatable, as can skinfold testing. This will allow you to monitor changes in your BF%, even though the actual BF% may be off considerably.

3) BIA scale and testing error increases as the BF% smaller and smaller. In other words, BIA is more accurate for a 25% BF person than a 10% BF person, but with that said, its still repeatable. Skinfold testing tends to be just the opposite, becoming more accurate with lean people, primarily because of the improved accuracy and repeatability of measuring the actual skinfolds.

4) Neither BIA or Skinfold calipers should be considered an absolute, as the potential error is simply too large.

5) Also, be careful with skinfold testing done by gym employees/trainers. My wife is everybit of 100lbs and between 3 different skinfold test, two of which were on the same day, here tricep measurement alone differered by 13mm and that was between the two tests on the same day. My point is these a good percentage of these people are not trained or experienced with skinfold caliper testing. Between 3 SF tests at 24fitness they have my wife at ~30% BF. Anyone with a brain could look at my wife and tell you that number was crap. Between 4 other and entirely different methods (handheld BIA, BIA scale, accumeare and slimguide) by wife is been checking around 19-20%. So 24fitness is different by 50% error. Anyway, let me get off that soapbox.



My recommendation:

Keep your scale. It is a useful tool to help keep tabs on your nutrition and training regimen. Take your BIA testing to first thing in the morning. Per the manufacterer, this is not the right time, BUT it will give you the most repeatable results, as you are in a fasted state. Most of us eat 5-6 meals a day, so once the days is started there really is not other opportunity to take a BIA without is being effected by something we have eaten or water content at that particularly time.

Consider a SlimGuide caliper too. I use both, as this give me that extra data point to positively say, yes I increase BF as both BIA scale and caliper are in aggreement, or if they differ, then I consider the data suspect for possible error. My BF% between the two differ by about 3-4%, but they generally show the same trend.

[TurboGuy]

there's no way a scale can measure your body fat just by standing on it. all a scale can measure is your weight. i'm amazed that people fall for this. Just thinking about it for 5 minutes should make you roll your eyes at the entire idea.

Please investigate Bioelectrical Impedance Analysis before spreading misinformation.

[Yep.]

Turbo, I appreciate the time you took to offer an explanation. In the end, it's based on how you look in the mirror. I agree that the bf scale should be used as a diagnostic tool to calculate only increases or decreases relative to some starting value (however off it may be).