http://www.gonintendo.com/s/222552-unconfirmed-wii-fit-u-sells-under-20k-in-u-s-for-january

It appears the source is from Neogaf (so obviously it's unconfirmed).  They were able to conclude that Wii Fit U < 20k.  So that's very dissapointing numbers if true.  But to be honest what did Nintendo expect, they way they have handled Wii Sports Club and Wii Fit U with little to no marketing and little retail presence is failing.  The real question is how much did this end up costing Nintendo?

VGC says it´s sold 20k+ in it´s first week

Hasn't the game been available digitally since last year though? And didn't they have this crazy offer where you could download the demo for free, and then just buy the pedometer-thingie for $20 or something, after which the demo would be turned into the full game, without any additional charge...?

and VGC is massively overtracking it.

NPD leaker said under 15k for the whole month

And that it had 48k preorders....

48k preorders, to 23k first week, to less than 20k first month.  At this rate, first year sales will be zero.

Or negative sales like the European Wii U shipments.

I wonder why anyone bought this beacause you coud unlock it with a Fit Meter.

I didn't even know Wii fit u got released, did it only come out digitally?

That offer to buy just a pedometer and get Wii Fit U for free was a steal.
Wii Sports Club and Wii Fit U both try out new methods of payment for games. This trend is further followed with this Rusty's Baseball (I think that's the name) on 3ds. I dont think the number of traditional copies should be worrying.
Now, how many pedometers were/will be bought is a different question. I doubt Nintendo will ever show the numbers.

Even Stevie Wonder saw that Wii Fit U wouldn't do anything when released in a market like today, I believe I covered this exact subject in the UNITY thread.

Fit meter made the actually game itself overpriced. 20 vs 50.