When taking part in running events such as a 10K, you'll often see bananas on the post-race nutrition tables. Bananas also often make it onto the list of recommended foods to eat before a race. While the fruit has certain benefits, eating bananas alone won't improve your personal record time. When combined with other foods, however, bananas can make up an important part of your pre- and post-run nutrition plans.
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Bananas have nutritional benefits that can help you fuel your muscle glycogen stores. Athletes often gravitate toward bananas because of their potassium. You need at least 4,700 milligrams per day and more if you're losing potassium through sweating during exercise, Colorado State University Extension reports. One large banana supplies 487 milligrams of potassium, or about one-tenth of of your daily requirement. One large banana also contains 31 grams of carbohydrate, the preferred fuel source during exercise, along with 3.5 grams of fiber, which helps moderate glucose absorption and prevents hypoglycemia, or low blood sugar.
Potassium and Bananas
Because bananas are high in potassium, they're often recommended as a way to prevent or treat cramping during or after exercise, since potassium depletion could contribute to this problem. Despite their ubiquitous presence on the post-race nutrition tables, bananas may not increase potassium levels enough to affect cramping if you eat them after exercising, a study published in the November-December 2012 issue of the "Journal of Athletic Training" found. Potassium levels increased only marginally; levels didn't rise until 60 minutes after ingestion of one banana and 30 minutes after eating two bananas. Many foods, including 3/4 cup of tomato juice or a cup of yogurt, supply as much or more potassium.
Bananas and Carbohydrate
Carbohydrates are the preferred fuel before exercise because your body breaks them down quickly for energy, unlike protein and fats. Eating 40 to 100 grams of carbohydrate before exercising helps keep your blood glucose levels up, registered dietitian Sharon Howard explains on the ESPN Training Room website. A large banana combined with another carbohydrate such as yogurt, toast or cereal can provide the energy you need.
Comparison to Other High-Carb Foods
While bananas are a high-carb food, they might not have any benefits for performance over other high-carb foods as a fuel source before exercise, a 2012 "PLoS One" article reported. The small study compared performance and certain blood test parameters in 14 cyclists who consumed either banana or a 6 percent carbohydrate drink before exercising. A study published in the March 2000 issue of the "Journal of Sports Medicine and Physical Fitness" found similar results when comparing bananas to other high-carb foods on a 10K treadmill run in the heat.