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Jason Segel

Jon Kopaloff/FilmMagic, Jeffrey Mayer/WireImage

Jason Segel is looking quite skinny lately.

The How I Met Your Mother star has been going healthy and getting in better shape for his upcoming movie Sex Tape.

"I've just been living healthy, exercising, eating right—no more midnight pizzas," Segel told Us Weekly this week. "This time when I take my shirt off, I've made a promise to myself, it doesn't have to be funny."

Jason Segel

Jon Kopaloff/FilmMagic, Jeffrey Mayer/WireImage

Yes, Segel, who's gotten naked for the camera before, will be taking his clothes off for the sexy flick. "I took heat for Forgetting Sarah Marshall, where I was completely nude," the 33-year-old said. "But different characters require different body types."

Segel costars with Cameron Diaz in Sex Tape, a comedy about a married couple who search for and try to retrieve a lost porn video they made of themselves. "It is R-rated," he dished, adding, "and I'm not in shape for no reason."

For more on Segel's weight loss, tune in to E! News tonight at 7 p.m. and 11:30 p.m.!