EXCLUSIVE

A very large teen claims the "Rachael Ray" show is more brutal than CrossFit, more grueling than P90X, more intense than "The Biggest Loser" -- and it all ended with humiliation and anxiety.

Christina Pagliarolo -- who weighed in at 260 lbs -- agreed to be part of a segment on overweight teens. She claims in her lawsuit ... the trainer made her run like Forrest Gump, yelled and screamed at her, and made her hike in the mountains.

Worst of all, she says the trainer put her on a StairMaster and kept cranking up the speed until she fell off the machine ... and then he yelled at her for falling.

Christina says she was a mess after training ... suffering serious injuries including messed up legs.

Christina is suing for negligence and intentional infliction of emotional distress.