When Gary Anthony Williams had a routine physical in April 2001 before filming the spy spoof Undercover Brother in Toronto, the news wasn't good. "I can't weigh you on this scale," the comic actor (Malcolm in the Middle) recalls being told. "It doesn't go that high." The doctor then mentioned John Candy and Chris Farley—"anyone who's dead and fat who'd worked in Canada," says Williams, 36, who then topped 360 pounds. "I thought, 'Now would be a great time to seriously get in shape.'"

He has kept at it. By working out daily and cutting down on carbs, the 5'11" Williams has shed eight inches from his waistline and more than 50 lbs. (and counting). So when he showed up to reshoot scenes as Brother's gadget-inventing scientist, he didn't look like his old self. "I was like, 'Gary, we need continuity here! Eat some pasta!'" says director Malcolm D. Lee, who instead put Williams in a fat-suit. Now his pals figure he should quit while he's ahead. "He'll lose too much," quips Malcolm's, Bryan Cranston, "and people will mistake him for Denzel."

Fat chance. But he wouldn't mind getting Denzel's dramatic roles. In the Williams family—he was one of 10 children of retired baking-company foreman Willie, 78, and his homemaker wife, Johnnie, 70—"everybody is funnier than I am," says the Georgia native. Classically trained, he performed Shakespeare onstage before moving to L.A. in 1998 and landing a gig on Malcolm. But his downsizing had nothing to do with the pressures of Hollywood. "I've never been ashamed of how I look," says Williams, who lives with wife Leslie, 38, a project manager, in a three-bedroom home in North Hollywood. "I've changed the way I live. I'd like to be around a long time."