Whether she's working with hockey players, gymnasts or long-distance runners, Canadian registered dietitian Nanci S. Guest gives medal-seeking athletes the same advice about eating: timing is everything.

"Olympic athletes need more fuel than most people and have to be much more diligent about when they get it," says Guest, who coauthored the 2009 nutritional guide for athletes for the International Olympic Committee. "Athletes need to eat in preparation for exercising, to take care of their bodies during exercise, as well as right afterward for recovery."

Fuelling up for a workout
Eating immediately before a workout isn't always a good idea. "Some athletes need a full four hours to digest, so if they're warming up for an early-morning marathon, breakfast is at 3 a.m.," says Guest. And because so many are anxious and can't eat before a competition, they end up relying on a meal before bed to propel them toward the podium.

"It actually works because muscle fuel -- muscle glycogen -- stays in your muscles until you use it," she says. Then, there are mid-workout snacks. "If athletes are exhausted after an hour of physical activity, it's not because their fitness level is low; it's usually because they're dehydrated or have run out of fuel." Fortunately, it's nothing a glass of Gatorade can't fix. Guest is a fan of sports drinks because they replace carbs, electrolytes and fluids in one quick hit.

Replenishing your body
Most important is what an athlete eats after exercise. Athletes in training can't afford to let their nutritional stores get depleted, and the window of opportunity to adequately recover begins to decline right after every workout.

At the top of Guest's list of high-glycemic "recovery" carbs are dates and raisins, because they're in your bloodstream in two to three minutes, or bananas, also a good pre-workout snack for an easy-to-digest energy hit. Her favourite recovery food after an intense workout, though, is low-fat chocolate milk, which quickly replaces lost protein and muscle glycogen, ideal for muscle repair. "I have most of my athletes drink 500 millilitres after every workout or event."

Power food
Although supplements played a key role in sports nutrition a few years ago, Guest has recently returned to a "food first" approach. "A poor diet with a supplement is still a poor diet," she says. Instead, she's a big advocate of plant foods. From lettuces to legumes, plants are packed with antioxidants you just can't get in supplement form. And athletes need extra antioxidants because strenuous exercise increases the number of free radicals in their bodies, a problem often exacerbated by training in smoggy cities.

Guest advises that athletes eat five to 10 or more servings of fruit and vegetables a day, depending on the athlete's size and physical expenditures, to get the full benefit of free-radical-fighting antioxidants. "Every plant has a different combination of these micronutrients -- a blueberry is very different from an apple, for instance -- so eating a variety of plant foods is best. I tell my athletes to eat a rainbow every day."

Photography, Jens Norgaard Larsen and iStockphoto.com.