Karl-Anthony Towns is going OFF on all the trolls talking down on his GF Jordyn Woods' recent body transformation ... saying he's personally seen her put in the work -- and it's ALL natural.
Woods was the center of awful social media criticism this week after posting a "before" and "after" pic from her fitness journey ... with some claiming her new look was manufactured.
But KAT is having none of that talk ... shooting down any notion Woods went under the knife in a passionate Twitter rant on Thursday.