Rob Kardashian's Weight Loss Plan -- Vows to Fight the Fat After Wedding Meltdown

Rob Kardashian is determined to drop his considerable gut after fleeing Kimye's wedding in fat shame ... vowing to hit the gym EVERY DAY until he sees his toes again, Rob's trainer tells TMZ.

Celeb trainer Gunnar Peterson tells us ... Rob texted him when he arrived back from Italy, where he bailed on Kimye's wedding because he felt too fat to pose for family photographs.

Gunnar says Rob's text was clear as crystal -- he wanted to hit the ground running ... literally ... posting up workouts every day this week, and continuing the intensity until the fat is gone.

As we reported, Rob's gym regimen hit a lull before Kim's wedding -- he worked out just a couple times a week -- but we're told Rob is now determined to get his old body back.

Gunnar tells us ... he will show Rob no mercy -- he'll endure a full hour of high-intensity full body exercises, cardio, resistance training ... the whole hog -- daily.

Gunnar tells us ... "Rob is locked and loaded" ... and NOT with cheeseburgers.