Sure. It's likely to be a few pounds of water weight, but it will help you look lighter, says Michele Olson, PhD, a FITNESS advisory board member. "Do a workout that makes you sweat a lot the day before," she says. A good 45-minute routine: "Alternate 60 seconds of vigorous cardio with 60 seconds of total-body strength moves," says FITNESS advisory board member Jeanette Jenkins, who puts her clients through similar pre-red-carpet sweatfests. And don't skimp on H2O. "Start drinking eight cups of water per day two days before and up until your event, cutting back to six the day of," Olson suggests. "It dilutes sodium in your blood, preventing water retention."