Since carbohydrate is the body's main fuel source during endurance exercise, it's important to begin an endurance event with plenty of it in the system. The body stores carbohydrate as glycogen in the muscles and liver, and slowly depletes those stores as the marathon miles pass.
Distance runners, then, whether competitive or recreational, are not likely to believe that cutting carbohydrate from the diet is the cornerstone of healthy eating. Still, the mid-pack marathoner looking to shed a few pounds may well have come across statistics that make some versions of these diets seem tempting. Research shows that in the first six months of a low-carb diet (20 to 100 grams daily), obese people can lose twice the weight and fat of low-calorie, low-fat, high carbohydrate dieters.
As with all foods, there is a limit to the utility of carbohydrate consumption, even in endurance athletes. What, then, is the right amount of carbohydrate to consume--both daily and during a long run or race? With carbs, how much is enough?
Think Grams Per Day
When planning your carbohydrate intake, think grams per day rather than percentage of total calories. Interval training and easy long runs will deplete glycogen similarly, but these workouts use substantially different caloric amounts. Your caloric need will vary even further between training and recovery days.
For athletes in periods of heavy training, a good rule of thumb is to consume three to five grams of carbohydrate per pound of body weight per day. Low-mileage runners and smaller people can get away with up to a third less. A 120-pound recreational marathoner needs perhaps 200 grams of carbohydrate daily. If this were a competitive athlete, the number would be closer to 400 grams daily. A competitive, 170-pound runner might range between 500 and 700 grams daily.
Carb Content in Foods
This may seem like a lot of carbohydrate. A pound of cooked pasta contains only about 126 grams of carbohydrate. A quart of Gatorade contains 56 grams. That's a lot of food to still place you firmly on the low end of the scale, but fruits and vegetables, sauces, condiments and even milk all contain additional carbs.
A cup of pasta sauce contains 14 grams; a serving of peanut butter seven grams; salsa and ketchup have about four grams each per serving, and at two tablespoons, a serving of salsa is quite small. Two slices of rye bread contain about 28 grams of carbohydrate, the amount in one performance gel. The bread in a large, thick sub has approximately 72 grams.
Fruits and vegetables are carbohydrate-rich foods that also contain a great deal of other nutrients, and it is widely known that you should eat them in plentiful amounts. But don't cut potatoes, bread and pasta from your diet. The cult of carbohydrate cutting notwithstanding, world nutrition experts assembling recommendations for the International Olympic Committee advise choosing foods high on the glycemic index as your major carbohydrate choices, especially for recovery meals.
The 24 hours prior to a long run or marathon are particularly crucial for building glycogen stores. Similarly, it takes 24 hours after an event to replenish those stores. Meals on a day of heavy marathon training should follow these guidelines:
Divide the number of hours prior to exercise by two to find the amount in grams of carbohydrate you should consume per pound of body weight. This ensures that you properly decrease the size of the meal as the time before exercise decreases.
Ideally, four hours before exercise, you would consume two grams of carbohydrate per pound of body weight. If you only have one hour to go, you should only consume one half gram of carbohydrate per pound.
Again, as a practical matter, smaller runners may consume up to a third less and favor consumption over longer periods of time. A 120-pound runner would not be able to consume 17 slices of rye bread with four hours to go before a long run. Since this has much to do with the sheer bulk of such a meal, remember that sports beverages and juices offer a concentrated dose of carbohydrate before a race, while filling the stomach far less.