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Marathoners differ wildly in their consumption strategies during a race, but there is a way to make sense of the science and enjoy an optimal pattern of fuel intake. Sports gels like PowerGel and Gu are convenient, low in fiber and easy on the stomach.
Since the body can store, at most, about 22 miles' worth of carbohydrate, these gels can help you avoid the dreaded Wall and guide you to a strong finish. Yet there are limits to their effectiveness. How many gels should you optimally consume during a marathon?
The Gatorade Sports Nutrition Advisory Board advises 30 to 60 grams of carbohydrate intake per hour during endurance exercise. This rate assumes full glycogen stores before starting, and has a competitive athlete pushing the limits of their ability in mind. For a four-hour recreational marathoner, averaging the two values means consuming 180 grams of carbohydrate during the marathon. This is an eight-ounce cup of Gatorade every other mile.
Since the typical energy gel contains 28 grams of carbohydrate, you can substitute one gel for every two cups of sports drink. For example, on a 12-mile training run at 8:00 pace, that would be two and a half gels, or two gels plus eight ounces of Gatorade -- if you're really pushing yourself.
Research has shown that taking more than two gels per hour -- even while foregoing sports drink -- does not improve performance. These estimates are for rigorous exercisers. They are based on people working at 65 to 75 percent VO2 max, or marathon race pace. This amount of consumption would be excessive for a training run at 50 percent VO2 max.
Performance gels can be easier to consume on the run. And members of the Gatorade Sports Science Institute point out that energy gels are useful in events where the need for carbohydrate is greater than the need for fluid, such as in open-water swimming or colder marathon temperatures. You must always take these gels with fluid, however, or you run the risk of slowing the absorption of both the carbohydrate and the fluid.
Many marathoners consume an excess of gels over the course of a race. Remember that each time you stop at a fluid station for a cup of sports drink, you are consuming 14 grams of carbohydrate per eight-ounce serving.
Even if you consume only four ounces of Gatorade every fourth mile, you'll take in nearly 46 grams of carbohydrate during the race. Also be sure to allow 15 to 20 minutes for the gel to take effect, and don't take more than one gel at a time. This will only slow the body's absorption of the carbohydrate.
A gel at mile 18 is a good idea. Another at mile 22, with, say, 40 minutes to go, may also help. But a mid-pack runner who takes two or three gels at mile 22 should not expect to launch miraculously across the finish line. And with 15 minutes to go, there is no performance advantage to taking further gels.
Because glycogen stores take a full day to replenish, it's important to refuel as soon as you can after a long run or marathon. The experts agree half a gram per pound of weight each hour is an optimal rate until you sit down to a big carbohydrate-rich meal.
Taking carbohydrate with protein may speed replenishment of muscle glycogen, particularly over the first 40 minutes post-race. Edward Coyle, PhD, FACSM, a researcher of Kinesiology and Health Education at the University of Texas, notes that protein is particularly useful when frequent carbohydrate feedings after a marathon are not possible.
(Sports Foods for Athletes: What Works?, Gatorade Sports Science Library, 1998, RT 32, Vol. 9, No. 2, www.gssiweb.com)