EATING TWO TO FOUR HOURS BEFORE RUNNING
Runners are often advised to eat several hours before exercising to allow enough time for the stomach to empty. The rationale is that if any food remains in the stomach when you start running, you can become nauseated when blood is diverted from the stomach to the exercising muscles.
Rather than getting up at the crack of dawn to eat, however, many folks who run in the morning simply forgo eating. This overnight fast lowers your liver glycogen stores (the source of blood glucose) and impairs performance during prolonged runs (over several hours) that rely heavily on blood glucose. During long runs, you rely heavily on your preexisting muscle glycogen and fat stores. Although the preexercise meal doesn't contribute immediate energy, it starts to provide energy when you run longer than an hour. It can also prevent you from getting hungry, which in itself may impair performance.
Eating a high-carbohydrate meal two to four hours before morning exercise helps restore liver glycogen, which will help during long runs. If your muscle glycogen levels are also low, the meal can also help increase them as well, as long as you eat several hours before your run.
Does the form of the carbohydrate eaten two to four hours before exercise influence performance? Probably not. Sherman and colleagues found that cycling performance was improved by 15 percent when subjects consumed a liquid carbohydrate (a glucose polymer drink) four hours before exercise. Darrell Neufer and colleagues at Ball State University found that cycling performance was improved when subjects consumed a mixed meal (cereal, bread, milk, and fruit juice) four hours before exercise.
Try different liquid and solid carbohydrates two to four hours before running to find out what works best for you. Sherman's research suggests that you should consume one to four grams of carbohydrate per kilogram of body weight, one to four hours before exercise. To avoid potential gastrointestinal distress, reduce the size of the meal the closer it is to the exercise. For example, a carbohydrate feeding of one gram per kilogram of weight (four calories per kilogram) is appropriate an hour before your run, whereas four grams per kilogram of weight (16 calories per kilogram) can be consumed four hours before your run.
Examples of good high-carbohydrate foods for prerace meals include fruit, bread products (adding jam or jelly increases the carbohydrate content), sports bars, and nonfat or low-fat yogurt. Fruit juices and nonfat milk are good high-carbohydrate beverages. You can also use liquid meals (see Table 1) .
Liquid meals have several advantages. They leave the stomach more rapidly than regular meals, which helps to avoid nausea. Liquid meals also produce a low stood residue, which helps keep immediate weight gain to a minimum. Because they don't contain fiber, liquid meals are also less likely to necessitate a bathroom break during your run.
You can concoct your own home-made liquid meals by mixing milk, fruit, and nonfat dry milk powder in a blender. For more variety, add cereal, yogurt, and flavoring (vanilla and chocolate). Sugar or honey may also be added for additional sweetness and carbohydrate. There are also several brands of "instant breakfast" powders that can be mixed with milk.
EATING ON THE RUN
Eating carbohydrates during runs lasting an hour or longer enhances endurance by providing glucose for your muscles when they run low on glycogen. Thus, carbohydrate utilization (and, therefore, energy production) can continue at a high rate and endurance is enhanced. Eddie Coyle and colleagues at the University of Texas in Austin have shown that consuming carbohydrates during cycling exercise at 70 percent of VŠO2max can delay fatigue by 30 to 60 minutes.
As the muscles run out of glycogen, they take up more blood glucose, which places a drain on the liver glycogen stores. The longer the run, the greater the utilization of blood glucose by the muscles for energy. When the liver glycogen is depleted, the blood glucose level drops. Though a few people experience symptoms indicative of hypoglycemia, most runners are forced to reduce their exercise intensity due to leg muscle fatigue.
The influence of carbohydrate feedings on running performance has also been evaluated. During a 40-kilometer run in the heat, Melinda Millard-Stafford and colleagues at the Georgia Institute of Technology in Atlanta found that a liquid carbohydrate feeding (55 grams per hour) increased blood glucose levels and enabled runners to finish the last 5 kilometers significantly faster compared to when subjects consumed a drink that didn't contain carbohydrate. In a treadmill run at 80 percent of VO2max, Randall Wilber and Robert Moffatt at Florida State University in Tallahassee found that when subjects consumed a carbohydrate drink (35 grams per hour) the run time was 23 minutes longer (for a total of 115 minutes) compared to the run when subjects consumed a carbohydrate drink (92 minutes).
What Form of Carbs?
Does the form of the carbohydrate consumed during exercise influence performance? No. Manuel Lugo and colleagues at The Ohio State University found that liquid and solid carbohydrate feedings were equally effective in increasing blood glucose levels and improving cycling performance.
Coyle's research suggests that you should consume 30 to 60 grams of carbohydrate (120 to 240 calories) for every hour of exercise. Try experimenting with both carbohydrate-rich foods and sports drinks. Sports drinks containing 6 to 8 percent carbohydrate are a practical source of carbohydrate. They provide the right proportion of water to carbohydrate to provide energy and replace fluid losses. Drinking 5 to 10 ounces of a sports drink containing 6 to 8 percent carbohydrate (about 56 to 77 calories per 8 ounces) every 15 to 20 minutes supplies the right amount of carbohydrates.
High-carbohydrate foods (see Table 2) provide a feeling of satiety that you won't get from drinking fluids. Eating one banana or four graham crackers or four fig bars or one sports bar per hour provides the recommended amount of carbohydrates.
Sports bars, fig bars, and cookies have a very low water content so they are compact and easy to carry. By comparison, high-carbohydrate foods that have a high water content, such as fruit, take up more room. For example, to get the amount of carbohydrate supplied by one PowerBar (47 grams), you'd have to eat 1.5 bananas (45 grams).
However, the low water content of some solid high-carbohydrate foods also has a downside. You'd better drink plenty of water when you eat solid food, especially a sports bar. Otherwise the food will settle poorly, and you may feel like there's a rock in your gut. In addition to aiding your digestion, drinking water while eating solid foods helps keep you adequately hydrated.
Try to eat or drink your carbohydrates before you feel tired or hungry, usually within 30 to 60 minutes into your run. Consuming small amounts at frequent intervals (every 30 to 60 minutes) helps prevent gastrointestinal upset. Your foods and fluids should be easily digestible, familiar (tested in training), and enjoyable (so you'll want to eat and drink them).
Consuming a high-carbohydrate preexercise meal adds to the benefit you get from consuming carbohydrates during exercise. David Wright and colleagues at The Ohio State University found that cyclists who consumed carbohydrates both before exercise and during exercise were able to exercise longer (for a total of 289 minutes) than those who consumed carbohydrates during exercise (266 minutes) or just before exercise (236 minutes).
However, the improvement in performance when carbohydrates are consumed during exercise was greater than when carbohydrates were consumed before exercise. My advice is that if you want to have a continuous supply of glucose during exercise, take in carbos during exercise.
EATING AFTER RUNNING
Consuming carbohydrates immediately after prolonged training and competitions lasting several hours increases muscle glycogen storage and helps you to recover faster. John Ivy and colleagues at the University of Texas in Austin compared glycogen storage when carbohydrate consumption was delayed for two hours after exercise. When the carbohydrate feeding was delayed for two hours, glycogen storage was cut in half when measured four hours after exercise.
Does the form of the carbohydrate influence muscle glycogen syntheses? No. Michael Reed and colleagues at the University of Texas in Austin found that postexercise liquid and solid carbohydrate feedings were equally effective in promoting muscle glycogen repletion following cycling exercise.
Replacing muscle glycogen stores after exercise is particularly beneficial if you train hard several times a day because you will get the most out of your second workout. Ivy's research suggests that you should consume 1.5 grams of carbohydrate per kilogram of body weight within 30 minutes of completing your run, followed by an additional 1.5 grams per kilogram feeding two hours later.
Many runners aren't hungry after heavy training. If this is the case, consume a high-carbohydrate drink such as fruit juice or a commercial high-carbohydrate supplement (see Table 3) for your first feeding. This practice also promotes rehydration. Then, your second feeding can be a conventional high-carbohydrate meal.
Remember that for the endurance athlete, carbohydrates in either liquid or solid form constitute the primary fuel for going the distance, whether it's the standard 26.2-mile marathon or the 24 Hours of LeMans . . .er . . . a 24-hour track race.
From The Ultimate Sports Nutrition Book. Reprinted with permission of Bull Publishing.
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