Recall that in a high-GI meal, carbohydrates enter the bloodstream very quickly, whereas in a low-GI meal, carbs enter the bloodstream at a lower rate. In studies involving a more sensibly timed pre-exercise meal, the glycemic index of the meal has had no effect on performance.
Choose foods and drinks that are not only easily digested, but also easily consumed—especially if you're prone to nervousness. Few athletes have their usual hearty appetite on race mornings, but the butterflies in their stomach usually permit consumption of soft, bland foods such as oatmeal and bananas.
A liquid meal such as a breakfast shake is another good choice, as long as it's high in carbohydrates and low in protein, fat and fiber. If you don't have a ritual pre-race meal, try various options and pay careful attention to the results. As with your pre-race dinner, once you've settled upon a pre-race breakfast that works well, stick with it.
Here are my choices for the five best foods to eat (or drink) before a race:
A bagel makes an excellent pre-race breakfast food, not only because it's rich in carbohydrates, bland and easily digested, but also because it's something many runners eat for breakfast routinely, hence familiar. Eat it dry or top it with something low in fat such as a light smearing of reduced fat cream cheese.
Bananas are almost all carbohydrate. A large banana contains more than 30 grams of carbohydrate, just one gram of protein and no fat whatsoever. Bananas are also high in potassium (400 mg), which is lost in sweat during running. As mentioned above, their softness and light taste make them easy to consume even with pre-race nerves, and their natural "wrapper" makes them handy for eating on the road.
Energy bars such as PowerBar and ClifBar are made to be eaten before exercise. Most are very high in carbohydrates and low in fiber, fat and protein. The better bars also contain useful amounts of sodium, potassium and the antioxidant vitamins C and E. A cappuccino flavor PowerBar, for example, contains 45 g of carbohydrate, 110 mg each of sodium and potassium, 35 percent of the recommended daily allowance of magnesium and 100 percent of the RDA of vitamins C and E.
There's a huge variety of energy bars on the market, and some are better than others. Choose one that's close to the PowerBar formula I just outlined. Avoid the high-protein, low-carb bars that have become popular in recent years.