Mischa Barton MBARTONVITAMIN0403_01.jpgEver wonder how Mischa Barton stays so slender? Well, we're no dieticians, but everyone knows about how important proper vitamin intake can be when it comes to weight management - and Mischa's clearly on top of her game! We spotted the ex-O.C. beauty keeping her electrolytes in check with a bottle of Vitamin Water while out and about on Monday afternoon. (It's a good thing, too - she'd end up needing her strength later that day!)