Aria shows different BF readings when gender is changed

[dogsbestfriend]

When i use the aria it gives me a seemingly accurate/ correct reading, but when my girlfriend uses it it gives her a reading that's 12% or so higher than she is (34% instead of 22%). if she changes her gender on her fitbit account, it starts giving her BF readings that are correct (12% lower).

My question is this, why would her reading change purely based on her selected gender? I know males and females have different ranges for 'normal BF %' but i would think that is reflected in the actual measurement. it seems strange for the scale to just tack on 12% because she's female?

any help is appreciated.

Moderator edit: updated subject for clarity

[Michael]

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@dogsbestfriend wrote:

When i use the aria it gives me a seemingly accurate/ correct reading, but when my girlfriend uses it it gives her a reading that's 12% or so higher than she is (34% instead of 22%). if she changes her gender on her fitbit account, it starts giving her BF readings that are correct (12% lower).

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The method the Aria uses needs to take gender, height, and weight into account to get the most accurate reading it can.

How does she know that 22% is correct?

@Dominique has previously posted a link that shows examples of what various body fat level look like. Does she look more like the 20-22% picture or the 35% picture?

[dogsbestfriend]

What i'm wondering is why does the gender affect her reading. if i step on the scale and select her profile when it asks, it'll give me a reading thats 10% or so higher than i get when i select my profile. similarly, she will get a reading 10%-12% lower when she selects my profile after stepping off than she does when she selects hers.

[Dominique]

It's not only gender: pretend you are younger/older, taller/shorter or heavier/lighter than you actually are, and the body fat estimate will change.

This is due to the way BIA scales work: they do not measure body fat directly (your Aria hasn't got "fat sensors"). What your Aria measures is a bioimpedance value obtained after sending a low-intensity current into your body through your feet. That value is then compared to a database of people who had their body fat % determined with a reliable method. So when your girlfriend steps on the Aria, her impedance value is compared to people in the database who are the closest to her in terms of impedance, gender, age, height and weight. It's quite unlikely there's a perfect match for her, so some extrapolation is taking place. If she pretends she's a guy, she will be matched against guys in the database with similar impedance, age etc. If she pretends she's 50, she will be matched against people in their 50's. So "lying" about any of her characteristics won't really be helpful. That changing gender gives a more accurate value is probably just a coincidence (what method was used to determine she's 22%, btw?).

That BIA can be off by up to 10% either way is a known limitation of the method.

[Roxbello]

My Fitbit Aria2 says I am 36% Fat. 

From the reference image you shared,

I look more like 25. In fact, a little like 21-22. If I had to select between the range of 21-22 vs 35, I look much closer to 21% (which is my body fat if I change my gender)

36 is absurd and not even in the picture.

it doesn’t make sense that the fat% would change due to gender. 

The healthy range varies for each gender, but the physical % should be the same for the same body. This doesn’t make scientific sense. It feels arbitrary and the device is starting to feel like an inaccurate fraud.

Fat% is what percentage of a mass is fat. Regardless of how tall or short the mass is or what the gender is. The mass has a % of fat, and if you make it longer or more squashed it should still be same.

Age and height remain the same as it’s my same profile. I changed my gender in the app to test this absurd issue.

A man with my **ahem** would be fat. It doesn’t make sense that if a man had my exact body fat disrtributed across his body when it’s in fact lsss natural for a man to have so much butt fat, it would be considered a lower number, if anything that’s should be the other way around. This make no sense. I feel scammed.

Moderator edit: merged reply

[JuanJoFitbit]

@Roxbello Welcome to our Fitbit Community! I'm sorry to hear that your Aria scale is not providing accurate body fat percentage. The Aria scale uses your gender, height and weight in order to calculate your body fat percentage. In case your body fat is not accurate, I'd like you to try to restart and re-calibrate your Aria by taking out the batteries for 15 seconds and put them back in. After this, weigh yourself 5 times in a row in order to refresh your scale.

Also, make sure that your Aria is placed on a hard surface and you are stepping on it barefoot and still.

If the issue persists, let me know and I'll be happy to follow up! 

[ClarDold]

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@dogsbestfriend wrote:

when my girlfriend uses it it gives her a reading that's 12% or so higher than she isender?

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If "Male" gives a better reading than "Female", it's because the database is looking for comparisons with typical female readings (as noted in another reply).

Aria 2 Help 
On your profile for the Aria 2 scale, you can select a display of Body Fat Percentage and/or BMI.
There is also a setting for "lean" and "regular".
If you know what the measurement actually is, you might check the effect of the lean/regular setting.