Has anyone taken zyprexa and not gain weight? If so, how did you do it?

I am physically active individual who eats well. My Pdoc suggested i try zyprexa for a mood stabilizer. He said if I only drink water , eat apples, oranges and carrots when hungry, and don't eat 2nd helpings, I shouldn't have problems with weight gain. Usually the notorious weight gain comes on in the lst 2 weeks.