If you want to slim down ASAP, face the facts: Rapid weight loss isn’t just unhealthy, it can set you up for binge eating and fluctuations that interfere with the results you want. Another thing: It’s hard! “For most people, it’s very, very difficult to lose more than one to two pounds of body fat in a week,” says Philadelphia-based weight-loss physician Charlie Seltzer, MD. And although water loss might move the scale a bit more, the change is superficial and temporary. “It’s fat loss that changes shape,” he says. Even if you manage to meet your goal, it probably won’t be sustainable: “The amount of restriction required will make you so hungry that you’ll eat everything in sight—it’s survival instinct,” Dr. Seltzer says.