Ideally, during extensive exercise that lasts for more than 60 minutes, you should try to balance your water and energy output with enough fluid to match your sweat losses and enough carbohydrate to provide energy and maintain normal blood sugar level. You can significantly increase your stamina by consuming about 100 to 250 calories (25 to 60 g) of carbohydrate per hour while performing endurance exercise, after the first hour (ACSM, ADA, and Dietitians of Canada 2000). Research involving cyclists suggests that sports beans, sports drinks, and gels all offer similar performance benefits. (Campbell et al. 2007).
Better yet, mix up your foods and fluids so that you get a variety of types of carbohydrate. Instead of just sports drinks, choose a sports drink and a banana or (part of) an energy bar plus extra water. Because different sugars use different transporters, you can absorb more carbohydrate and have more fuel to support your endurance exercise (Jentjens et al. 2006). Engineered sports foods commonly contain only one or two types of sugar, so don't hesitate to experiment with natural foods that offer more of a variety of carbohydrate.
During a moderate to hard endurance workout, carbohydrate supplies about 50 percent of the energy. As you deplete carbohydrate from muscle glycogen stores, you increasingly rely on blood sugar for energy. By consuming carbohydrate during exercise, such as the sugar in sports drinks, your muscles have an added source of fuel. Sports drinks also help maintain normal blood sugar levels. Because much of performance depends on mental stamina, you should maintain a normal blood sugar level to keep your brain fed and help you think clearly, concentrate well, and remain focused.
Your body doesn't care if you ingest solid or liquid carbohydrate; both are equally effective (Mason, McConell, and Hargreaves 1993). Despite popular belief, even sugar can be a positive snack during exercise (see chapter 6).
For snacks during exercise, some people prefer the natural sugars from fruits and juices, some choose gels or energy bars, and others prefer sports drinks or hard candy. You need to experiment to determine which foods or fluids work best for you and how much is appropriate.
Is more carbohydrate better? Not if the source of carbohydrate just sits in your stomach. In a study of trained women cyclists who did two hours of moderately hard endurance cycling, consuming a beverage that supplied 60 grams (240 calories) of glucose per hour resulted in the highest amount of carbohydrate being used. When the women drank a beverage with 90 grams of glucose (360 calories) per hour, they did not perform any better—likely because the fuel sat in the stomach unabsorbed and contributed to intestinal distress. With the lower carbohydrate intake, only a few subjects complained about feeling bloated. With plain water, there was only one complaint (Wallis et al. 2007). If the women had consumed a variety of forms of carbohydrate, perhaps they would have had fewer complaints.
Keep in mind that too much sugar or food taken at once can slow down the rate at which fluids leave the stomach and become available to replace sweat losses. Be more conservative with your sugar fixes during intense exercise in hot weather, when rapid fluid replacement is perhaps more important than carbohydrate replacement. In cold weather, however, when the risk of becoming dehydrated is lower, sugar fixes can provide much-needed energy.
Because consuming 100 to 250 calories or more per hour (after the first hour) may be far more than you are used to consuming during exercise, you need to practice eating during training to figure out what foods and fluids do or do not work. That is, you need to train your intestinal tract as well as your heart, lungs, and muscles. Alex, a novice marathoner, tucked hard candies, gummy bears, and chocolate mints in a waist pack that he wore on his long runs. He also hid along his running loop a cooler containing gels, pretzel nuggets, a banana, and bottles filled with water and the sports drink that would be available on the marathon course. Between the snacks and the fluids, he was able to maintain adequate energy during his three-hour training runs and simultaneously learn what he liked to eat during exercise. On marathon day, he assigned friends to specific checkpoints along the route. Their jobs were to keep him well supplied with a variety of these carbohydrate sources. He never hit the wall, and he was pleased with his time.
Whatever the situation, endurance athletes such as marathon runners, ultradistance cyclists, and Ironman triathletes need to make a nutrition plan far in advance of the event and experiment during training to learn if they prefer grape or lemon sports drinks, solid foods or liquids, energy bars or Twizzlers, raisins or bananas.
By developing a list of several tried-and-true foods that taste good even when you are hot and tired, you need not worry about what to eat (and what not to eat) on race day. Ideally, you should have a defined feeding plan for the event and know the following:
Like Alex, you should also figure out how to have these foods and fluids available for you during your training and competitions. If you have a support crew, instruct them to feed you on a defined schedule so that you can prevent hypoglycemia and dehydration.
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