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Are Body Fat Scales Useless?

Posted by Joel Marion

Over the weekend I got a phone call from my friend Natalie.

She was a bit frustrated, and understandably so.

You see, about a week ago (per my recommendation) she purchased an electronic body fat scale to track her progress as she attempts to diet down for “beach season”.

Unfortunately, for the last week, the readings have been all over the place.

“One day it says I’m 26% and then the very next day somehow it reads 22%. Then back up to 24% the next day. It makes no sense.”

Perhaps you can relate.

Without a doubt, these scales can seem pretty worthless if you don’t really understand a) how they work, and b) how to use them to produce reliable, consistent data.

On the other hand, when you’ve got “A” and “B” down pat, body fat scales can be an invaluable tool to easily track body composition without having to bust out a pair of calipers or set up an appointment to have your body fat evaluated at your local gym (which has its own set of accuracy problems).

Today I’ll clear up the confusion and tomorrow you’ll actually be able to use the body fat function of your scale to produce some meaningful data.

First, let’s cover how they work:

Electronic body fat scales use a technology called bioelectrical impedance (BEI) to assess body fat.

With this method, a very light, unnoticeable electrical current is passed through the body and the percentage of the current that is repelled and the percentage “absorbed” or conducted are both measured.

The assumption is that body fat will repel the current while all lean tissue will act as a conductor, leaving the percentage repelled as your estimated body fat percentage.

Here’s the problem:

This method is highly dependant on consistent levels of body water, something that is not often consistent to say the least.

This is where both your and Natalie’s frustrations come in.

For example, if you just exercised or are dehydrated, the measurements will be off. If you have a different level of body water than when you last measured, the measurements will be off. If you take your body fat in the morning, and then again in the evening, the measurements will be off.

In other words, in order to get consistent readings, you have to be consistent in your measurement practices; this is what I recommend:

Body water is at it’s most stable point every day first thing in the morning before eating and drinking anything. This is when you should be taking your body fat readings.

Another recommendation is to only measure at most twice weekly. There are too many fluctuations that happen from one day to the next, and it’s flat out psychological torture to be stepping on the scale every day.

I do not allow my clients to get on the scale but once a week-period. And if they email me with concerns about scale weight being up from yesterday, I simply respond with “Give me an update on Saturday morning.”

Be consistent with your measuring practices and you’ll be surprised just how consistent your measurements become.

And lastly, always use multiple methods of tracking progress-scale weight, body fat %, and girth measurements are all part of the equation (with the most important of those being girth measurements; if clothes are getting loser and “problem” measurements are going down, you are undeniably getting leaner, regardless of what the scale says).

So how about you? Do you use a body fat scale? What other methods do you use to track progress?

At least 100 comments and I’ll be back before you know it with more VIP blog content!

Talk to you in the comments section,



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147 comments - add yours
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@ Per:
I think body fat scales are useless. You recommend to weigh first thing in the morning, which is what I do. The result can range from 17% on a ” good” day to 21.5%. Most of the time it is around 19. This 4.5 % difference makes the result useless. Furthermore, there is a similar scale at my gym. It says my BF% is 14-17%, where most of the time is says it’s 15%. Yet another scale told me multiple times my BF% is 11%. Like how the hell do you get from 21.5 to 11 to 20.5 within a week? I don’t trust those devices anymore.

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I use a Tanita model that was reasonably priced. Measures weight, body fat % and body water % for both male and female and average or athletic build. How accurate is it? Doesnt matter, pick a setting and stick with it.

If your weight stays the same and your body fat is going down you know your getting leaner or maybe the opposite depending on your reasults. I use it once a week unless I see a large fluctuation in body water % then I will measure again the next day.

I DO NOT measure first thing in the morning due to water building in your core after sleeping and that could throw off the readings. I measure in the early evening and the results seem to be more consistent.

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You’re absolutely right about this; the fluctuations you can get from not measuring consistently can make significant differences in body fat percentage.

I find that if you always weigh yourself at the same time under the same circumstances (like first thing in the morning right after waking up and before taking a shower, completely naked) give you the best results.

That way you take most of the variances such as food intake, clothing, etc. out of the mix.

I also agree with you that doing it on a daily basis (been there and done that) can be almost obsessive; and the daily fluctuations can be really inaccurate even if you do measure consistently.

Looking forward to seeing the next post.


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I use a bodyweight scale from Tanita, it was recommended in Joel’s Cheat Your Way Thin program. I weigh myself in the morning at write down weight, lean mass, body fat % and hydration %. It’s still jumpy, but i know i’m getting the physique i want, so sometimes i say forget the scale, forget the numbers, i can see what i’m becoming =) I also take monthly measurments with a measuring tape.

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I have a weight/fat % machine and I only get on it in the morning before eating/drinking/workouts due to all of the fluctuations and I have found that it is fairly consistent. But I don’t rely on just the machine…measurements, the way my clothes fit and the mirror confirms what I already know…I need to lose serious fat %… Also…just for grins n giggles the % will go up after a BM…

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Did I miss the VIP blog content? I’m on Cycle 2, day 2 and am really longing for somewhere to connect to others who are doing XFLD – any plans for a forum or even a blog where you’re talking about it with others who are going through it? It’s so extreme that I can’t really talk about it with my normal workout friends – they’ll think I’m insane for doing so many hard workouts without ANY rest days.

I was kind of hoping your new blog would help out with that….but whatever it is you’ve got up your sleeve, I’m looking forward to seeing it!

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I agree that getting on the scale daily can be a big reason for failing motivation.
Has anyone ever seen the method used by the military to compute bodyfat? For men it is basically the waist measurement, at the navel, minus the neck measurement, parallel to the long axis of the neck at the base of the adams apple. You take that number, the circumference value, and find it on the left ahnd column of a chart go over to your height in inches and that gives you your bodyfat.
For women they use a similar method but it is waist + hips – neck = circumference value.
Anyone think that has a high accuracy rate?

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thanks for the very useful and enlightening info. I will now be able to use my body fat monitor scale and hopefully progress towards reducing my body fat percentage What is the ideal body fat percentage for a 52 year old female?

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Thanks for blog entry and thanks for the comment about psychological torture. My Tanita experience has been exactly that. Torture. I was taking the reading every evening before eating (their recommendation). Figured out fast the trick to getting the BF reading I wanted by drinking lots of water. But even the weather affects it. During the winter when it’s dry in the house, I was not as hydrated and therefore got bad BF readings. Now that it’s spring and more humid, my hydration level is better so I get better readings.

The main problem that i have is that the Tanita has always given me a BF reading of lowest 17% and highest at 21% (like i said, based on hydration level). But when I use my calipers, I am consitently below 10% BF and that is using averages, in case I don’t always pinch the same way or same area.

So I don’t know what to think. Is my body 19ish% BF (based on Tanita) or 9ish% (based on my calipers).

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I get the best results first thing in the morning right after I shower. My scale requires damp tootsies, y’see.

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Well, I use callipers. Still having trouble getting used to them and there are a lot of different places to measure. I’d love it if you could outline the ideal way to get your body fat % with callipers.

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The body fat thing is tricky. I agree that bioelectrical impedance scales and devices are highly dependent on several factors. However, other than the gold standard “underwater weighing”, it’s probably the least invasive and easiest for people to use. Just make your testing under consistent conditions.

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There is one reason for which I have trust issues with these scales. If they really work the way they are supposed to, they should be able to tell your approximate fat and water % without such info as sex, weight and age. I mean, a body is a body regardless this extra info. Using this info to adjust and “refine” the result is very biased imho. It doesn’t consider that a woman or an older person can be pretty fit. If you change these data and put there the same body, it will show you incredibly various results, for the same body! I can’t really put much trust in such a machine, which is bad for me as this is the only means I currently have. So I just check it after each cycle and look at the changes but I can’t take the numbers seriously, though I really would like to see the exact result.

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Regarding comments about body fat scales: Please note that I recently had problems with a brand new body fat scale not registering at all. I tried over and over again to get a reading, but it just kept reading “error”. When I called the company, their first question to me was, “do you have any metal in your body?” My reply was “yes”, I have two small rods in my lower back from a spinal fusion I had. They told me that I would not be able to get a reading on my scale because the metal interferes with the wave that is sent thru the body. Just thought I’d let everyone know!

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Good sound advice Joel

The thing is to not get hung up on the varying fluctuations.

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Does anyone know how to make the tanita read a lower body fat percentage? I heard if i am dehydrated that it will make it read a lower body fat percentage. Is this True even if its not accurate?

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My water percentage is currnetly under 50%. my fat is at 9%. Feeling great

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Never believed to these scales, they seem to rely on the weight, height and gender, like I measured it once and then instantly drank 1.5 liters of water and my bf% reading went up while hydration decreased. I think they are very inaccurate. However, these stupid fitness “pros” and stores are still not selling calipers in my country and I couldn’t even find the non-fitness calipers in normal household stores. What’s going on in this country I don’t know. But when the scale and the mirror and clothes tell different things I rather believe the latter.

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Excellent post at Body Fat Scales – Useless? | Body Transformation Insider. I was checking continuously this blog and I am impressed! Extremely useful info specially the last part :) I care for such info much. I was seeking this certain information for a very long time. Thank you and good luck.

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Nice post at Body Fat Scales – Useless? | Body Transformation Insider. I was checking continuously this blog and I am impressed! Extremely helpful info specifically the last part :) I care for such information much. I was looking for this particular information for a long time. Thank you and good luck.

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Body Fat Scales – Useless? | Body Transformation Insider Very nice post. I just stumbled upon your blog and wished to say that I’ve really enjoyed surfing around your blog posts. After all I will be subscribing to your feed and I hope you write again soon!

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I’m not sure I fully understand what you mean.

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