Too bad—cheating is expressly forbidden. “[S]uccumbing to any other foods, as small as the lapse may be, will be like puncturing a balloon with a needle,” warns Dukan. The Attack phase lasts between one to 10 days, depending on how much weight you have to lose. For the majority of dieters—those with 20 to 40 pounds to shed—Attack is typically five days and weight loss is usually four to seven pounds, according to Dukan.