[Shop-talk] Un-warping butcher block countertop?

[Jim Franklin]

I have an Ikea desktop made with solid 1" square lengths of who knows what wood. Probably birch or beech. It's 30 x 60 and exactly an inch thick. I don't see the product on their website anymore but it looks a lot like this:

https://www.instructables.com/Butcher-block-countertop-table-IKEA-hack/

I gave it to a friend who turned it into a guest bed with 4 short legs. I (200 lbs) slept on it for a few weeks. There are 2 metal straps underneath to hold the glued joints together.

Fast forward 6 months and I have it again and am using it as a kitchen island countertop, but it has gone concave along the length, as if my weight warped it. I don't think it's a moisture imbalance issue because it's always been open to the air on both sides. I've loosened the metal straps but the wood is still warped. Is this something that will slowly un-warp as the weight of the island base pulls down on it? The base is 2 old bookcases back to back, and I've screwed the countertop to them with L brackets. Currently the lighter bookcase is slighty off the ground, being held up by the warpage. 

I'd like to eventually bind the two bookcase backs together but I don't want to split the countertop. 

thanks,
jim