LOS ANGELES — The only way Taylor Lautner was going to reprise his “Twilight” role of Jacob Black in “The Twilight Saga: New Moon” was to change.

That’s because Jacob has to evolve from being an average teen-age boy to a muscled young man who transforms into a wolf.

“Jacob transforms a lot in ‘New Moon,’ not only physically but mentally and emotionally as well. So it was a matter of getting into the gym and eating the right foods and also reading and studying the book and my character,” Lautner says.

Lautner mixed exercise and high-calorie meals to build the body that gets revealed repeatedly in the movie. The more than 3,200 calories he needed daily to be able to add the muscle mass was accomplished by eating every two hours.

Director Chris Weitz says that while the audience identified Lautner with the role after “Twilight,” there was a possibility the part could have been recast if Lautner did not get himself ready for the film.

“But I was always convinced he was going to be able to do it. Doubts came up because he had very few scenes in the first movie and because he is described as being 6-foot-5 in the second book. So there were some reasonable facts we had to come to grips with,” Weitz says.

“I like the sweetness of his character in the first movie,” he says. “I knew it was easier to take an actor in the direction of anger and rage than it was to find some sort of ‘hunkster’ Native American and somehow turn him into that very sweet nature that Taylor brings out to boot.”

Lautner wasn’t sweet on everything in the movie. He hated wearing the long black wig he needed in the early scenes because it kept getting in his mouth. There was a celebration when he got to pitch the wig and switch to a short haircut.

Keeping the role of Jacob means Lautner has to deal with the same intense publicity spotlight that’s been shining on his co-stars Kristen Stewart and Robert Pattinson since “Twilight.”

Lautner says there is no way to prepare for the stardom phenomenon.

“We were just filming a movie that we wanted the fans to enjoy,” Lautner says. “And then it kind of just blew into this whole other world.”