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From Superbad to super-slim!

Known for his rotund shape, comic actor Jonah Hill was tasked with a weight-loss challenge for his latest upcoming movie: Before he could fight crime on 21 Jump Street, he had to battle the bulge!

The 5-foot-7 star, 27, wanted to drop 30 pounds before production began in April on the action film, based on the '80s TV hit starring Johnny Depp.

But a pal tells Us Weekly that Hill "went on a diet for the movie, but gained weight at first!"

"Finally, he got a nutritionist and a trainer," the pal explains. And Hill showed off his svelte new shape in L.A. March 2. "Now he looks better and feels better!"