The question: Will one "cheat day" a week ruin your weight-loss plans?  

The expert: Rachel Beller, M.S., R.D., author of Eat to Lose, Eat to Win

The answer: No, in fact, it's encouraged! "Usually after three to four weeks of an intensive weight-loss plan that I design for my patients, I introduce the food vacay," says Beller. She tells her clients to pick one (mandatory!) day a week to take a break from calorie counting. Just like you need a break from work, your diet needs some wiggle room to keep you focused and motivated. So why does she wait a few weeks to introduce it? When you're just starting a weight-loss plan, you're already driven and you're fueled by seeing results, says Beller. But later, when you may be losing steam, introducing a cheat day can help make dieting more sustainable.

But Beller does have a few rules to make sure these vacations don't ruin your waistline. It's not an invitation to binge, she says, so you shouldn't plan to pig out all day long. "Organize it around a meal, or just say that you'll be more relaxed about your lunch and dinner," says Beller. And just like a real vacation, do a little planning. Knowing that you'll order your favorite pasta and maybe cheesecake on Friday night will make it way easier to resist those stale cookies on Wednesday. Finally, let go of the guilt. You're giving yourself one day a week to relax, so it shouldn't feel like you're screwing up. And that's key since messing up on your diet can lead to a "What the hell?" attitude that makes you call it off altogether. 

One last tip from Beller: Have someone who helps you stay accountable—like your doctor, dietitian, or a super healthy girlfriend. They'll help make sure you cheat the right way without going overboard. 

More from Women's Health: 
Is It Normal to Feel Hungry All the Time While Dieting? 
3 Ways to Eat Healthy This Holiday Season 
The Dinner Habit That Helps You Stay Slim