For most people, weekends are a time to let loose—your schedule is more of your own making, your outfits don't need to be ironed or even color-coordinated, and there's more time to enjoy yourself with family and friends. But between Friday night happy hour and Sunday night munchies, a lot can go down the hatch and derail your healthy-eating and weight-loss goals. Here’s how to stay on track.

Tame the snack factor. Planned healthy snacks are fine (and can actually keep your hunger in check), but unintentional "because it's there" samplings will add up. In fact, a recent study found that adults eat about 230 calories more on the weekends than on weekdays, and that much of the extra calories came from fat. It may not sound like much, but it adds up: After several months, you've unwittingly taken in 3,500 calories—a full pound.

Enjoy your lazy Sunday … but work a little movement in. Find one hour on Sunday when you can do something physical—rake leaves, walk the dog, take a yoga class, play with your kids at the park. Here's why: A study in the journal Obesity found that people on diets stopped losing weight on weekends (and those who weren't on diets gained!) partially because they're less active on Sunday.

Make your healthy Sunday night dinner last all week. Sunday night is a good time to make a huge pot of soup or a big casserole. Not only will you end your weekend with a veggie-filled meal (and veggies fill you up for fewer calories), but you'll be giving yourself something healthy to grab during the week when you're too crazed to cook. Just freeze individual portions for microwavable lunches or dinners all week.

Beware of alcohol's calories. Studies show that one of the top sources of extra weekend calories is alcohol, so it pays to scale back your sips somewhat. If you're in Phase One or Two, you're avoiding alcohol all the time (right? right!). "Alcohol is caloric—some people can lose weight simply by cutting out alcohol—and it relaxes your inhibitions, making it harder to resist bigger portions," says Janis Jibrin, M.S., R.D., Best Life lead nutritionist. However, if you're in Phase 3, you're allowed off the wagon, so to speak. Try to keep drinks to one per night, and stick to wine and light beer (both are about 100 calories, tops); both of these have fewer calories per serving than mixed drinks, which can max out at 400 calories depending on how many liquors and juices are propping up that paper umbrella.

Don't Let Weekends Derail Your Diet, and other weight-loss and fitness tips from Bob Greene, Oprah's trainer.