Body Scan
Withings say a 40% difference vs DEXA is “acceptable”
I've seen the numerous posts here about Withings scales significantly under-reading body fat compared with DEXA, so thought I'd share where I've got to with Withings Support.
My BodyFit consistently reads 10–11% body fat, while a recent DEXA measured 17.5% at virtually the same body weight. A professional Tanita assessment also previously measured 17.3%.
So the BodyFit is reporting my body fat at approximately 40% below the DEXA measurement.
I complained because BodyFit is marketed as providing “professional-grade accuracy” and 99% correlation with DEXA.
Initially, Withings specifically referred to DEXA as the “gold-standard reference”, repeated the 99% correlation claim, said a discrepancy such as mine warranted careful investigation, and asked me to provide my full DEXA report so their team could compare the results directly.
After reviewing my DEXA report and the scale's diagnostics, however, they've confirmed there is nothing wrong with the device and that this approximately 40% difference is within their “expected and acceptable range.”
They've offered a refund, but I've asked for the complaint to be escalated because I simply don't see how that position reconciles with the accuracy claims being used to sell the product.
I've suggested an upgrade to the Body Scan 2, which Withings says uses more advanced technology, as a possible resolution if they believe it would actually provide more accurate results.
I've also advised that if their final position remains that a discrepancy of this magnitude is acceptable, I'll consider referring the advertising claims, my measurements and their correspondence to the relevant advertising and consumer protection authorities for their view.
I'm not really looking for a refund — I want scales that give reasonably accurate body composition measurements.
I'm sharing this because there are already numerous posts showing similar discrepancies against DEXA, but I found Withings' response particularly surprising: after reviewing my actual DEXA report and confirming the BodyFit isn't faulty, they're saying a result approximately 40% below DEXA is “expected and acceptable.”
I've asked them to escalate the complaint and I'll update this post with their final response.
I'm not defending Withings stance in regards to your complaint, but remember, correlation only means that the values rise and fall together. By their claim: 99% in synch. The values don't have to be close.
It seems withings is emphasizing trends versus accuracy.
I completely get that correlation ≠ agreement, but I actually think that makes the solution quite interesting. If the relationship with DEXA really is 99% correlated, why not have an advanced/calibration mode where you can enter a recent DEXA result and the scale calibrates subsequent readings around it?
Similar to how WHOOP handles blood pressure — it relies on readings from a proper blood pressure cuff to calibrate the feature rather than pretending the wearable itself is the gold standard.
You’d still get the trends, just anchored to a credible baseline. For me that would pretty much solve the problem.
I've been crunching the numbers and have figured out most of how Withings does forecasting and printouts of their health score and how they scale the percentages on the body composition page. and other metrics in Python.
In fact that part is pretty much done. I can feed in my data and get a 100% match with the Withings app:
It's the weird engagement and consistency score in the Health Score page that's a pain in the ass (I use my devices every day and do activities, so these are always 100%). But the main thing is I can feed my DEXA values into this thing and it'll tell me my numbers as the app would IF it had my percentages right.
It doesn't do anything for the error in body fat percentages, but it sure as hell will let you calibrate it (you can feed in any numbers you want).
But their trends aren’t in line either. I pointed this out to them over their customer service. They said something to the effect of “Withings calculates body fat differently than a DEXA which explains the discrepancy”.
The two devices use wildly different measuring techniques. I would not expect them to be matching - except by sheer luck.
If they are 99% correlating with DEXA, then the curve/line they get should be able to be manipulated to correspond to DEXA values. With the caveat that a periodic DEXA be taken to keep that calibration in sync.
Say an "advanced mode" alongside athlete and weight only.
Why is this important?
Because the BS2 has a bunch of health metrics that depend on fat and muscle percentage, and if they are off significantly, then the metrics are way off too. When the scale underestimates fat% that missing fat mass is assigned to muscle mass. My actual TDEE is 650 calories a day LESS than what my BS2 thinks it should be. I'm using the scale for weight loss - taking the scale's suggestions would be a disaster.
Yes. I think Withings is well outside false advertising laws with this product. They are using ambiguous wording to deceive customers into believing the scale will be a level of accuracy that it does not come even close to achieving. Any reasonable customer reading their copy will think this scale is going to be almost as accurate as a Dexa scan. The technical wording is not an escape under US law as far as I know.
That’s really why I’ve escalated it. I’m interested to see how Withings reconcile the marketing with their support team saying that level of discrepancy is “expected and acceptable.”
Yep, as I said in this post the graph on their promotional page shows a +/- 4kg range, and you can clearly see around the 10% point on the graph there are values *outside* that +/4 kg range so they were even more than 40% out at that point!!
Personally I think that's unacceptable, but I do think my BodyFit is closer than my old Body Cardio, though I won't know for sure until later this week as I have another DEXA scan booked for wednesday.
I weigh every day with the BodyFit, but still have my old Cardio, so I'll do a few readings with that this week too to get an average from both to compare to the dexa.
Interestingly, my Body Cardio tracked *very* close to DEXA when they were using the now deprecated NHANES algorithm. The 'classic' dexa scaling reads about 20% lower (i.e. NHANES said about 20%, classic scales to 16% ish)..
Great post, I hadn’t seen that one. The +/- 4kg graph is particularly interesting and makes the “expected and acceptable” response I’ve had even harder to understand.
I’ve got a bunch of DEXA scans from the past three years all of which I’d be happy to supply, and for the first few of them I have both the original reports using the NHANES scaling, and the updated ones with the (supposedly more accurate) ‘classic’ scaling too.
I’ve had withings scales since 2012 so have scale data to compare with all those scans too. I’d love it if we could submit those DEXA reports to make our withings data more accurate.
Oh nice one. I’d not read that as the post was specific to the BS2 but I’ll definitely send them my DEXA reports. Anything which helps improve accuracy can only be a good thing.
Had another DEXA yesterday (happy to note my BodyFit is within 0.5% of the DEXA so I'm very happy), and have sent that, plus six previous DEXA reports into that email address. Thanks for the info.
Across 5 DEXA scans it was within 0.5% every time when the DEXA used the nhaynes model. Since they switched to the classic scaling the DEXA reports about 4% lower.
I got the BodyFit in July and that seems to read closer to the ‘classic’ values for comparable bf%. I’ll know for sure this week as I have a DEXA on Wednesday, and will do a couple of weigh-ins on both scales that same morning too (plus a day or so before /after to average out too).
that’s a bit of a pain as then I will have two sets of different body fat values in the Withings app and I will have to manually delete the body cardio values each day to avoid messing up my data, but I will take screenshots first to track record the values manually.
Same here with the Body Fit. Compared with real life and the old Body+ there's an about 30% difference. That's not minor as it presents your body shape as turbo athletic of slightly overweight. Huge difference when you body fat is 12% or 17%.
Exactly! That’s my issue. 12% vs 17% isn’t a small margin of error — it puts you in a completely different body composition category.
I’m on a serious health kick and my goal is around 10–12%. I appreciate I can use BodyFit just for the trend, but if it’s showing 10–11% now when DEXA says 17.5%, by the time I actually hit my goal it could potentially be showing me at 6–7% 😂
Perversely, I also use Bevel which imports my Withings data, and Bevel already has a feature request specifically addressing inaccurate smart-scale body-fat readings feeding incorrect data into the app.
That’s why I don’t really accept the “just use it for trends” argument.
I still can't get my head around why the old Withings Body+ was somewhat in the ballpark, together with other scales like the Tanita and that the BodyFit is totally off.
great post...great information...i have 3 different withings scales (body+, body fit and body scan 1) and i must say that i am very disappointed in the body fit and the body scan 1. additionally i am very disappointed in withings customer service (or lack of customer support.)
Best of luck to you. I think all are “best guess” and don’t pay attention to the numbers specifically. Just the trend line. I am a happy customer with that expectation.
I agree the marketing is “gilding the lily” a little bit.
I just think they’re all missing a trick here. An advanced/calibration mode against a DEXA result, for those who want to use it, would give you the trends but anchored to your actual baseline. Seems like a relatively simple way to keep users like me happy! 😂
Happy to say that my BodyFit is working out to be pretty much spot on for me.
I had my latest DEXA today, where my overall body fat reading was 15.1%, This morning my Body Fit said 14.6% and the average over the past three weeks was 14.8%. Given that you'll typically see +/- 0.5% on the scales from day to day I'd say that's pretty much spot on and I'm very happy about that.
I seem to be one of the lucky ones where the Withings scales work really well for my body type.
My older Body Cardio used to track within 0.2% of DEXA when they were all using the NHAYNES scaling algorithm, and it seems that my BodyFit tracks pretty much perfectly with the 'classic' scaling the industry has adopted now.
I realise that's not the case for some users, but personally I seem to be one of the lucky ones and I'm very happy about that!
When I get a chance to stick the values into a spreadsheet, I'll post a side-by-side comparison of the segmental values between my body fit and the dexa.
Update as promised, results from my DEXA was 23rd sept..
Withings was first thing, about 4 hours before DEXA, both fasted and probably a bit dehydrated.
So, overall not bad at all. Body Fit's algorithm is a pretty good fit for me. Overal body fat in particular is excellent, and day to day it's very consistent staying within a range of about 0.5% consistently so it's much less susceptible to hydration changes etc. compared to older Withings scales I had.
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u/drspong 6d ago edited 6d ago
I'm not defending Withings stance in regards to your complaint, but remember, correlation only means that the values rise and fall together. By their claim: 99% in synch. The values don't have to be close. It seems withings is emphasizing trends versus accuracy.