Jessica Simpson has stunned fans by shedding an estimated 25 pounds (11.3 kilograms) in a month. The pop star/actress hired celebrity trainer Harley Pasternak to help her get back in shape after a little careless eating left sexy Simpson feeling fat. Pasternak put his star client on a strict 1,300-calorie-a-day diet, delivering his own nutritional meals to her doorstep. The trainer's 5-Factor Diet and Fitness plan has also been adopted by Vanessa Williams, Katherine Heigl and Simpson's on-off boyfriend John Mayer. Pasternak admits he's impressed with Simpson's weightloss: "We're making Jessica taut and toned without taking away her femininity."