What’s the skinny on Seth Rogen’s svelte new self?

“The lamest answer ever,” he said Friday on Ryan Seacrest’s KIIS-FM radio show, “I exercised and I dieted.”

He added, “I personally do not care how I look or physically feel.”

He said he had to lose weight to play a newspaper-publisher-turned-vigilante in the big-screen adaptation of The Green Hornet, which begins shooting next April.

(He recently told E! News he isn’t sure how many pounds he lost. “I don’t weigh myself,” he said.)

His girlfriend of nearly four years, writer Lauren Miller, isn’t fazed by his new look.

“She’s stuck by me through thick and thin – literally,” Rogen said. “She claims she doesn’t like me any more now than when I was heavier, but I think that’s completely not true.”

She also digs his raunchy new Kevin Smith comedy Zack and Miri Make a Porno (out Oct. 31).

“It’s a very romantic movie,” Rogen told Seacrest. “My girlfriend likes it and she hates porn.”

While filming, “I was around a lot of body parts…but I dealt with it very maturely,” he said. “It was a very good lesson in anatomy.

“I think I’ve been researching this movie since I was 11 1/2 years old,” he added. “That’s around when the research started.”

Rogen – who bared his bum in Knocked Up – said he doesn’t show much skin this time around.

The actor deadpanned, “I tried to give everyone a break with this one.”

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