Extract from the December 2011 issue of Runner's World

MOST RUNNERS KNOW they should eat pasta, rice, potatoes, or other high-carb foods before a half or full marathon. After all, carbs are a great source of energy, and you need a lot of energy to cover 21.1 or 42.2 kilometres. But many runners are far less clear on how many carbohydrates they should eat and when to start loading up. “When I go to marathon expos,” says Monique Ryan, author of Sports Nutrition for Endurance Athletes, “I’m amazed how many people haven’t carbo-loaded properly. Runners train so hard and then arrive with a huge handicap.” Here’s what every runner needs to know about carbohydrates, so you can toe the line fully fueled and ready to go.

CARB SCIENCE
When you eat a bowl of spaghetti, most of the carbs are stored as glycogen in your muscles and liver. Glycogen is your body’s most easily accessible form of energy, but it’s not the only source, says Meade. During a half or full marathon you burn both glycogen and fat. But the latter is not as efficient, which means your body has to work harder to burn it for fuel.

When you run out of glycogen during a race you hit “the wall.” Your body has to slow down as it turns fat into energy. Benjamin Rapoport, a 2:55 marathoner, is intimately acquainted with the wall. The Harvard M.D. student (who has a Ph.D. in electrical engineering from MIT) hit the wall so hard at the 2005 New York City Marathon he decided to study how to avoid it in the future (his research was published in PLoS Computational Biology in October 2010). “Proper carbo-loading – or filling your muscles to the brim with glycogen – won’t make you faster, but it will allow you to run your best and, if you race smartly, avoid the wall,” he says.

CHOOSE WISELY
Which carbs should you load up on? “I’m very utilitarian,” says Rapoport. “I eat rice for breakfast, lunch, and dinner.” But runners don’t need to be so restrictive. Breakfast cereals, breads, pancakes, yoghurt, and juice are all easy-to-digest options. Many fruits are high in carbs but mostly in the form of fructose and are also high in fibre – and too much can cause stomach trouble midrace. “Ripe bananas are a low-fibre choice,” says Anthony Meade, Adelaide-based sports dietitian. “And you can peel apples, peaches, and pears to reduce their fibre content.” He also gives permission to indulge in white bread and baked bread products like finger buns since both are easily digested.
Meade suggests steering clear of high-fat foods – like creamy sauces, cheese, butter, and oils – as well as too much protein – it is supposed to be carb loading! Both nutrients fill you up faster than carbs and take longer to digest, he says. Pick jam – not butter – for your toast, tomato sauce in lieu of alfredo sauce on your pasta, and low fat frozen yoghurt, ice cream or gelati for dessert.

HOW MUCH?
You can’t completely fill your muscles with glycogen from just one meal, “which is why you should start carbo-loading two or three days before your race,” says Meade. Since you’re running very few kilometres, the glycogen will accumulate in your muscles. At this point, 85 per cent of your energy should come from carbs, says Meade. He recommends eating about ten grams of carbs for every kg of body weight (for a 70 kilogram runner that’s 700 grams – or 11,000kJ – of carbs per day). During his research, Rapoport developed an even more precise formula, which runners can access at endurancecalculator.com, that factors in variables including age, resting heart rate, VO2 max, and predicted finishing time. It’s important to keep in mind that you’re most likely not eating many more kilojoules per day than you were during the thick of your training –it’s just that more of those kilojoules are coming from carbs.

If you step on the scale while you’re carbo-loading, be prepared to see a number that’s at least one to two kilograms more than your usual weight. The extra kilos mean you get a gold star for carbo-loading properly. “With every gram of stored carbohydrate, you store an extra two to three grams of water,” says Meade. That means your body will be hydrated and fueled as you start the race, ensuring you cross the finish feeling strong.

*Purchase the December issue of Runner's World *