You're well on your way to achieving your weight-loss goals. But going from couch potato to athlete overnight has left something to be desired – more food! So what's the best way to satisfy your ravenous appetite without erasing all your hard work? Nanci S. Guest, registered dietitian, certified personal trainer and head nutritionist for the XXI Olympic Winter Games, shares her nutritional dos and don'ts for the freshman fitness fanatic.

Do: Eat often. The best way to keep your body fuelled is by eating five or six smaller meals a day, between 300 and 600 calories each. Each meal should consist of two-thirds carbohydrates such as whole grains, fruits and vegetables, and one-third high-quality protein like fish, chicken or tofu. If you're pressed for time, plan ahead and always carry healthy snacks.

Don't: Exercise on an empty stomach. It's especially important to boost your energy before a workout, no matter how early your morning run is. "I recommend getting a little bit of protein and some carbohydrates into the bloodstream," Guest says. "Most importantly it's going to prevent amino acid break down, but it's also going to allow you to run longer. It's counterintuitive, but the ingestion of those tens of calories will result in a burn of an extra hundred."

Don't: Load up on fatty foods before a workout. According to Guest, it takes fats three to five hours to fully digest, and it's important to give your system at least two hours to process them. So, skip the post-dinner ice cream if you have an evening elliptical session planned.

Do: Refuel right after a sweat session. "After a high-intensity workout, you want to get something into your system immediately; you'll recover more quickly, and be able to work out just as hard sooner," Guest says. The enzymes that produce muscle-repairing glycogen are working at double the rate after exercising, and there's a brief window of time to take advantage of that accelerated process. Missing that opportunity results in longer recovery periods, and can keep you out of the gym for days at a time.

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Do: Drink chocolate milk. It gets to your bloodstream immediately, unlike a nutritious meal that needs to be both prepared and digested, and it's undeniably delicious! It replaces the sodium lost through sweating, and it's chockfull of amino acids, which are essential for repairing damaged muscle tissue. If you're concerned about calories, you can dilute chocolate milk or substitute it with skim to reduce your sugar intake, and if you're lactose intolerant or vegan, opt for soy milk.

Don't: Bother with protein powder. "Powders absolutely aren't necessary. It's a synthetic food, and if you're consuming enough calories, you can get plenty of protein from a variety of sources, which has proven to be better for your muscles," Guest says. Also, your body doesn't register liquid calories well, so you'll be left feeling hungry if you drink a powder mixed with water or juice.

Do: Eat real food. After guzzling some brown cow, you still have to get a well-rounded snack or meal in you within two hours of dropping the dumbbells. "I'm a big fan of smoothies," Guest says. "You can get some good fats in there with flaxseed or olive oil, and it's a great way to get a good dose of fruit, antioxidants in berries, and calcium and sodium in the milk products." She also recommends egg whites as a pure, fat-free, carb-free source of protein – they're terrifically convenient when pasteurized and packaged in a carton.

Don't: Blow it! Burning an excess of calories gives many people a sense of entitlement when poring over a menu or wandering the dessert aisle at the supermarket. Just because you're coming under your calorie count, doesn't mean your side of fries isn't disastrously high in sodium, or your slice of pie isn't brimming with trans fats - causing far greater damage than an added belt notch or two. Remember that making the right food choices will only get you to your goal faster.

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