You could eat as much as you wanted before a marathon, but for such a long race, it's almost inevitable that you'll still run out of energy - what runners call "hitting the wall" - if you only rely on the body's natural stores.
"You will manage a dawdle or slow jog at best," says Dr Duncan MacFarlane, sports physiologist at University of Hong Kong's Institute of Human Performance. This is because the body only stores enough energy for up to two hours of medium intensity exercise.
Carbohydrates are the body's main energy source. Carbs may be complex (such as legumes, grains and starchy vegetables) or simple (such as fruits and foods made with sugar). During digestion, the body converts carbs into sugars, which enter individual cells to provide energy. Sugar is stored in the liver and muscles as glycogen - your main energy source for a marathon.
To stay energised, MacFarlane recommends refuelling on the run. "One decent bite of a sports bar every 30 minutes, several mouthfuls of a banana, or an energy gel pack every hour with water will help."
Research shows you can also guard against the mid-race bonk by carbo-loading in the days leading up to a marathon. A study by Liverpool John Moores University published in the International Journal of Sports Medicine in 2011 got 257 male and female runners at the 2009 London Marathon to keep a detailed food and training diary, which the researchers compared with the runners' finishing times. Each runner's pace was also tracked every five kilometres throughout the race.
It was found that competitors who had consumed carbs the day before the race at a quantity of more than seven grams per kilogram of body mass had significantly faster overall race speeds and maintained their running speed during the race longer than those who consumed fewer carbs. The difference was especially striking beginning at about the 29-kilometre mark, just when many runners famously "hit the wall".
The key to race nutrition is finding out what works for you - and this can be done during training, says MacFarlane. Here are more tips on how to get the most out of your nutrition before, during, and after a marathon.
The target window for increasing your glycogen storage is two to three days before your race, says MacFarlane. During that time, increase your carbohydrate intake and decrease your training, or it will diminish your stores and counteract all that eating.
As a guideline, dietitian Sylvia Lam from Pro Cardio recommends taking in between seven to 10 grams of carbohydrates per kg of body weight and making carbohydrates around 75 per cent of your diet. Vary your carbohydrate sources to include potato, rice and other grains to avoid bloating.
MacFarlane suggests avoiding anything new or unusual during this time to keep things easy on the stomach. Steer clear of foods with high fibre content, such as broccoli, cauliflower or beans, as they tend to promote intestinal gas. "Avoid spicy foods, like curries, as they can irritate the gut," he says.
Lastly, go easy on meat the few days before a race. "Eating excessive protein before a race will not benefit your performance," he says. "It will not be used for energy production during the race, so it's better to focus on storing carbohydrates."
A 60kg person, for example, will need about 420 to 600 grams of carbohydrates per day leading up to the marathon, says Lam. Fifty grams of carbs is equal to about one bowl of rice, two slices of bread, one medium potato, 1.5 bowls of cooked pasta or 1.3 bowls of cereal. "So one might need to eat the equivalent of around eight to 10 bowls of rice," she says. Try sports drinks and juices to supplement your carb intake.
Resist the urge to pig out on the morning of a race as it may lead to stomach issues as you run. MacFarlane says a bland carbohydrate breakfast, such as toast, is best at least 90 minutes before the start of the race.
Finally, MacFarlane suggests a sugar hit just before the race, such as a handful of jellies combined with a sports drink.
During the race
What you choose on race day depends on your preference, but pick something easy to carry and easy to digest, such as energy gels. Aim to eat something every 30 minutes to one hour.
During a marathon, favour sports drinks over water or soft drinks, MacFarlane says. "A high-quality commercial sports drink that has about 5 to 6 per cent carbs in it, with some electrolytes, which include sodium and potassium, is ideal, as this provides a small amount of carbs to keep your energy going, plus enough water to keep you hydrated."
While factors such as temperature, humidity, running speed and sweat rate will affect how often you should drink, as a guide, you should try to drink around 400ml to 800ml per hour.
Once you cross the finish line, the recovery begins. "After a race, replenish with carbs for energy and protein for muscle repair," says Lam.
Thirty minutes after the race is crucial for repair. Your body is already producing enzymes enabling the body to repair itself, so additional protein helps to speed up the process.
A traditional remedy
Traditional Chinese medicine (TCM) remedies may help to reinforce a runner's physical well-being in preparation for a marathon, says registered TCM practitioner and chairwoman of the University of Hong Kong Bachelor of Chinese Medicine Alumni Association, Doris Mok Hang-yan. "It is important to keep a balance of yin-yang in the body," she says.
"Over-sweating may lead to a qi deficiency and yin deficiency."
Mok suggests making a tea with the following ingredients, which will help to tonify the qi and yin as well as quench thirst.
- 500ml-1,000ml water
- 6 grams sliced ginseng or American ginseng. This depends on your body type, so consult your TCM practitioner to determine what is right for you.
- 6-20 grams Radix ophiopogonis (dwarf lilyturf root)
- 6 grams Fructus schisandrae Chinensis (fruit of the Chinese magnolia vine)
Bring water to boil. Add all the ingredients and boil for 20 minutes.