How accurate is the Aria scale and How is it calculating BF%

[Beck_C]

I have had my Aria scale for many years and has never been calibrated, but I believe the weight is fairly accurate. The weight always seems to agree with the scale at my fitness center and my doctors office. However, the BF% is extremely discouraging. I maintain a very active lifestyle, always have. Through the Holidays (end of November through the EOY) I enjoy myself, stay true to my workout routines, but enjoy food, nothing over the top, just enjoy some extra goodness. Then after the first of the year dry January begins and restrict my calories back, way back to shed any unwanted weight from the Holidays. I have done this for years. I have also been frustrated with my Aria for years, my weight will trend downward, drop down a size or two in clothes, but the more my weight drops the higher the BF% goes up. Finally this morning (I only weigh on Thursday mornings) I had enough and decided for the first time since 2013 to reach out the FB community for any advice someone may have to offer me. And yes, I am very aware my Aria has some age on it, but this has been a long time issue. Thank you to anyone who respond or at least reads my rant. 

[JohnnyRow · Accepted solution]

Fitbit scales measure body fat % by bioimpedance, which only gives an estimate as is true of most methods.  It passes a small current of electricity into one foot and receives it in the other, measuring the body's resistance to the current.  Fat has a high electrical resistance, and muscle passes a current easily because muscle is higher % water.  So really it is measuring the amount of water the current encounters on the trip through your body.  Of course there are other factors that affect the amount of water in your body.  It is important to weight at the same time under the same conditions to try to equalize that.  Most suggest weighing in the morning after using bathroom.

But other factors also can affect fluid in the body that this method cannot account for.  For instance, As you cut back on food and start losing weight, it could be your body is proportionally losing more water, not just from muscle.  Water loss makes it look like less muscle, and more fat.  After a while of regular eating, the body adjusts to a constant amount of water retention and it even out.

You can see the same type thing sometimes when trying to lose weight but it stays the same, then all of sudden a few pounds come off, because your body just got rid of the extra water it was retaining.  And that water is what bioimpedance is actually measuring.

Or just google "bioimpedance" and maybe get a better explanation.

[Beck_C]

Thank you! That is great information. I will definitely research bioimpedance. Have a lovely day!  

[Heybales]

I'll add that some good ones (usually meaning they either do hands and feet, and add some additional measurements like neck or gender/age) can get a better statistical estimate and some studies have shown upwards of 5% accuracy - if the same hydrated body is presented.

That's hard to do.

Most are in the 10% range, if same hydrated body presented.

Move that up to 15-20% if not.

Meaning it is not intended to be useful for daily measurements at all that is meaningful, but rather for trend over months.

Consistent even if inaccurate can be useful there to see a trend.

If you get off and on and get a very different reading - not so useful.

Considering that women even with scale weight need 28 days due to known water weight fluctuations to get some figures that are meaningful, you cannot take a reading change from 5-15% as anything beyond water weight change.

Drink 16 ozs of water and you just gained 1 lb of LBM (Lean Body Mass - everything not Fat Mass) according to the readings.

Scales that give other figures besides the BF% are really relying on some statistical averages and those estimates are for entertainment. Sometimes you laugh, sometimes you cry.

[JuanJoFitbit]

Hi everyone! I'd just like to share this help article, which has a section that explains how you can get the most accurate reading on your Fitbit scale.

See you guys around.