There’s a little less of Jack Black to go around these days!

The lovably rotund star looks particularly trimmed and fit in his upcoming Vietnman War comedy, Tropic Thunder, and there’s a definite reason for that. After getting more than an eyeful of himself on a 40-foot screen, Jack decided it was time to cut the fat.

"When I saw my rear end in my nude scene in Margot at the Wedding, it actually had a double chin," he tells "I’ve joined a gym because the next time you see me naked I’ll be trim."

Although looking good in nude scenes is priority No. 1, health played a factor in the 38-year-old’s decision as well.

"I want to feel good too," he says. "Now If I eat a cheeseburger and fries, it tastes so good at the time and then right after it’s like, ‘What did I do? Why?’"

Tropic Thunder, co-starring Ben Stiller (who also directed the film) and Robert Downey Jr. revolves around three actors filming a movie about the Vietnam War. Craziness ensues when their director ditches them mid-production.

"I play kind of a Chris Farley-esque type , an actor, who is big into the excesses of the industry," Jack says of his character, Jeff "Fats" Portnoy. "He parties too hard. It’s about shooting a film about the Vietnam War film in Hawaii. My character is looking for a shot at an Oscar because usually he makes fart comedies. Come to think of it, I guess it kind of mirrors my actual reality."

The film hits theaters Aug. 15, but those longing for a dose of Black attack can check out the comedian in the animated Kung Fu Panda, which opened today. Since it was a voice role, Jack, who just welcomed his second son, did not get the chance to learn some martial arts and kick some ass — but he has in the past!

"When I was a kid, I took karate and judo classes," he says. "I even won a trophy in a judo tournament, but I confess I outweighed the competition by 20 pounds. I never took any kung-fu classes though, I just saw it on TV and in the movies."

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