The Diet That's Changing Hollywood

Where do the stars turn to when they need to lose weight fast? This week, Us examines the new diet and exercise plan that's whipping Hollywood into shape. Jessica Simpson has a problem that a lot of women can relate to. Whenever she fights with or breaks up with a guy, she finds comfort in food, a source close to Simpson tells Us. Case in point: the 5-foot-3 singer appeared to pack on pounds during her turbulent relationship with John Mayer, reaching 145 pounds in April of this year, according to estimates by NYC internist Marc Siegel. "Jessica was so frustrated when she saw that she was gaining weight," says the source. So Simpson put her body in the hands of celebrity trainer Harley Pasternak, whose 5-Factor Diet and Fitness Plan whittled the singer down more than 20 lbs by mid-June.

Want to learn the healthy eating secrets this former exercise-nutrition scientist has taught Simpson and other stars including Katherine Heigl, Mandy Moore, Eva Mendes and Vanessa Williams? Check out the new issue of Us Weekly, on newsstands this week.