Paul Zimmerman / WireImage 1 / 15
Paul Zimmerman / WireImage 1 / 15

Jonah Hill's drastic diet caused problems for the director of new comedy "The Sitter" after the funny-man began to lose weight during the shoot.

Hill was filming the movie last year (2010) when he decided to embark on a new healthy lifestyle and hired a nutritionist in a bid to slim down.

But filmmaker David Gordon Green admits it was a struggle to conceal the once-chubby star's transformation on the big screen.

He tells New York Post gossip column Page Six, "About two-thirds of the way through the movie, Jonah made a conscious decision to say, 'I want to get healthy, let's do this.'

"We shot the movie out of order, so that helped disguise it a bit, but there are some scenes where you can see his pants don't fit anymore. It forbid reshoots."