Julie Hall, 40, is trained in basic performance nutrition and is a seven-time Ironman competitor who runs marathons for fun. As training intensifies and mileage peaks for those participating in the Standard Chartered Dubai Marathon 2010, she says it is crucial that calorie intake is high enough to keep the body moving through the distance. Her main advice for anyone looking to participate in an endurance event is simple: "You have got to eat for what you are doing." Dieting is not an option.
"If someone comes to me to lose weight and wants to take up running as a hobby, that is one thing. But if they are training for a marathon then they must eat for that race and the training they are doing," she said. "It is possible to lose weight, but that has to be a secondary thing." Carbohydrates - found in breads, cereals, grains, fruits and vegetables - are an important element of any marathon diet, particularly those with at least 3g of fibre per serving. Trying to cut calories or eat a low-carb diet, Hall warns, can result in injury and illness.
"Eat little and often," she advises. "Have a decent breakfast, a mid-morning snack - not too heavy - a lunch with a cup of carbohydrates like pasta or rice, and a mid-afternoon snack. Then if you're going to do a lot of running in the evening you'll need to refuel with carbohydrates. "Many people think they will eat a light dinner to lose weight a bit faster. If they are not doing much training in the evening then yes, it is better to eat something more protein-based like chicken or fish with salad. But if you are training in the evening, then to eat pasta or rice in the evening is absolutely fine."
Greg Boucher of the fitness industry association MEFitPro warns women - who are typically more prone to worrying about their weight than men - to be aware of what he calls "the female athlete triad": disordered eating, or too few calories; amenorrhoea, which leads to an increase in stress fractures; and early-onset osteoporosis. Female runners, he says, need a minimum of 1,000mg of calcium a day to decrease stress-fracture risk - "If you don't get three servings of dairy daily, take a supplement" - and 18g of iron to avoid "weakness, fatigue and decreased physical performance". They should fight the temptation to be "fat-phobic" by including healthy fat in their diet such as that found in unsalted and unroasted nuts, peanut butter or olive and canola oils.
Male athletes are also prone to nutritional mistakes, such as piling on the protein in the assumption that it will increase muscle mass. "If you consume too much protein and not enough fat and carbs, you risk deficiencies and low energy levels," Boucher warns. "Getting enough fuel from healthy carbs allows the body to use protein for muscle building and not for fuel." The body only uses 2.2g of protein per kilogram of body weight for building muscle, he says. Though meal-replacement shakes or bars can help top up protein levels, food must come first.
"Runners need to focus on their diet rather than on which supplements to take to enhance their performance," he says. "Focus on your training, eating every three hours, hydrating properly and getting adequate carbs and protein." Boucher and Hall say that fuelling up within half an hour of completing a long run is crucial to repair and recover the muscles. "Even if you are not hungry, drink a chocolate milkshake or, if you have a protein shake, even better," Hall says. "If you have driven to the start of the run, take a cool box and have something to go back to the car with."
Junk-food lovers should try to eat as naturally as possible during the week and allow one day a week, possibly a Friday, when they take their long run, to eat what they like. "Have your pizza or whatever and then the next day get back to it," Hall advises. "You are still going to lose weight if you are training. It's all about discipline."