The energy used during running is derived from muscle glycogen (stored carbohydrate), muscle fat (stored triglycerides), and liver glycogen. One of the benefits of training is an increase in muscle glycogen stores and an increased ability to use glycogen and fat. Thus, we are able to exercise longer. Many runners ask me: Is it beneficial to consume carbohydrate before or during exercise? If so, what should I eat?

It is beneficial to consume carbohydrates before and during exercise only if the activity is longer than 60 minutes. If you are exercising less than this, there are no significant benefits from consuming carbohydrates before or during exercise. Eating a high carbohydrate meal before exercise "tops off" muscle and liver glycogen stores. In other words, it assures us that we have maximized the storage of glycogen. This delays the onset of fatigue, enabling us to exercise longer and perform better. Pre-Race Or Training Run Eating

Your weight, personal preference, and tolerance determine how much you should eat. Some runners cannot eat much before they work out, and they obviously would consume less than someone who can tolerate a larger meal before a workout. The general rule is to consume one to five grams of carbohydrate per kilogram of body weight one to four hours before you work out or compete.

To determine body weight in kilograms, divide your weight in pounds by 2.2. So, a 130-pound woman should consume 60 to 300 grams of carbohydrates and a 190-pound man should consume 90 to 450 grams of carbohydrates before a long training run or race.

One serving of carbohydrate contains 15 grams; serving size examples include four ounces of orange juice, a piece of fruit, half of a small bagel, one-half cup of pasta, three-quarters cup of dry cereal, or one cup of milk. An example of a 60 gram meal is three-quarters cup dry cereal with one cup of milk, and two servings of fruit. An easy way to plan a pre-workout meal is to read the food label for carbohydrate content and consume the recommended amount. Solid foods are better tolerated if consumed a few hours before running. If you are planning to eat one hour or less before you run, a liquid meal is recommended. Liquids are digested more quickly and better tolerated if consumed closer to running time.

Eating During Training Runs Or Races

If you plan on running for at least one hour, then you should plan to take in some carbohydrates during your run. Consuming carbohydrates during endurance activities provides an additional energy source and spares the supply of liver glycogen. With more energy, we are able to exercise longer and delay the onset of fatigue.

The recommended amount of carbohydrate is 30 to 60 grams of carbohydrate per hour. Energy gels and glucose solutions (energy drinks) are good sources of carbohydrate during exercise. The glucose found in drinks is diluted to the appropriate concentration (6% to 8%) and is absorbed more quickly than the gels. For this reason they are the preferred source of carbohydrate during exercise. You will need about 375 to 500 milliliters per hour of a sports drink to consume the recommended amount of carbohydrate. Gels are a good source but it is essential that you consume the recommended amount of fluid with the gels to assure that you quickly absorb the glucose without any cramping.

It is important that you experiment with eating during your training runs and figure out what works best for you. To minimize abdominal discomfort, do not try any new foods, drinks, or gels before or during a race.

Denise Feeley is a Registered Dietician with more than five years experience counseling and teaching nutrition, and lecturing to athletes, coaches, and athletic directors. She is also an avid runner.