Many studies show that you can exercise longer and more intensely and recover faster when you take a source of sugar during vigorous exercise. Dozens of brands of sports drinks are promoted to fill this need, but a new study from Appalachian State University shows that a banana appears to offer superior results, specifically helping athletes to recover faster from intense exercise (PLoS One, March 22, 2018). The red blood cells of athletes eating bananas produced much lower blood levels of a genetic precursor of COX-2, which causes inflammation that delays recovery, than those of the group that took sports drinks.
Fruits and their juices have lots of antioxidants and other nutrients that sports drinks do not contain. An earlier study by the same authors showed that fruit caused less inflammation than some sports drinks (PLoS One, May 17, 2012). Other studies have also shown that fruit juices can improve athletic performance better than sports drinks do (Am J of Physiol–Endo and Metab, December 2015).
Taking Sugar During Exercise Helps You Go Faster and Longer
When you exercise, your muscles use sugar, fat and a very small amount of protein as a source of energy. You have an almost infinite amount of fat stored in your body, but only about 600 grams of sugar, called glycogen, stored in your muscles and liver (2400 calories). Of course your liver can make new sugar, but it cannot make it fast enough to keep up with your needs during very hard exercise. The limiting factor to how intensely and fast you can exercise is the time it takes to move oxygen into muscles. Since fueling your muscles with sugar requires less oxygen than fat does, you have to slow down when you start to run out of sugar. Also, running out of sugar increases inflammation, damages muscles and delays recovery from exercise. When your muscles run out of their stored sugar, they hurt and you have to slow down and work harder. Runners call this "hitting the wall."
Your brain gets almost all of its fuel from sugar in your bloodstream. When your liver starts to run out of sugar, blood sugar level drops, your brain cannot get enough fuel to function properly, you feel tired and confused and can pass out. There is only enough sugar in your bloodstream to last three minutes. To keep your blood sugar level from dropping, your liver must constantly release sugar from its cells into your bloodstream, but there is only enough sugar in your liver to last 12 hours at rest, and far less than that when you exercise. During long and intense exercise, your muscles draw sugar from your bloodstream at a rapid rate, your liver can run out of its stored sugar and your blood sugar level drops. Long-distance bicycle racers call this "bonking."
How Fruits Help You Recover Faster from Intense Exercise
All fruits and their juices contain two sugars, glucose and fructose, either bound together or separate. Some sports drinks contain only glucose. Several studies show that cyclists exercise with less effort and have less gut irritation from drinks made with sucrose (regular table sugar, found in fruit juices), rather than the single sugar, glucose (Am J of Physiol–Endocrinol and Metab, December 2015). Compared to drinks that contain only one sugar (glucose), drinks that contain two sugars (glucose and fructose) help you to race faster in competitions lasting more than two hours (Applied Physiology, Nutrition, and Metabolism, April 2012). Drinks that contain both glucose and fructose include fruit juices, soft drinks made with high fructose corn syrup (HFCS) and any drink made with sucrose, which is regular table sugar. Sports drinks that contain only maltodextrin, (made from starches extracted from rice, corn, potato and whole grains) are not as effective for racing because maltodextrin contains just the single sugar called glucose. However, drinks that contain maltodextrin plus fructose are similar to drinks made with HFCS or sucrose.
Why Racers Need Both Glucose and Fructose
How much sugar you can provide to your muscles is limited by how fast you can absorb the sugar from your intestines into your bloodstream and then from your bloodstream into your muscles. Sugar is transported through the intestines into the bloodstream and then to your muscles by special carrier proteins called carbohydrate transporters. Each carbohydrate transporter is specific for each type of sugar, so if you eat two different sugars, you use two different carbohydrate transporters and therefore can take in more sugar. Sugar absorption into your bloodstream is increased by as much as 65 percent by taking both glucose and fructose, compared to glucose alone. According to one report, "The increased carbohydrate oxidation with multiple transportable carbohydrates was accompanied by increased fluid delivery and improved oxidation efficiency, and thus the likelihood of gastrointestinal distress may be diminished. Studies also demonstrated reduced fatigue and improved exercise performance with multiple transportable carbohydrates compared with a single carbohydrate" (Curr Opin Clin Nutr Metab Care, July 2010;13(4):452-7).
Avoid Sugared Drinks When You Are Not Exercising
Taking sugared drinks can cause very high rises in blood sugar, particularly if you are not exercising or are overweight or diabetic. Every cell in your body is like a balloon full of fluid. When blood sugar levels rise too high, sugar sticks to the outer membranes of cells. Once there, sugar can never get off. Eventually sugar is converted by a series of chemical reactions to sorbitol, which destroys the cells. This cell destruction causes all of the side effects of diabetes: blindness, deafness, heart attacks, strokes, kidney failure and so forth. Unless you are in the midst of vigorous exercise, I recommend that you use plain water to quench thirst.
If you plan to compete in sports lasting longer than an hour, you should take in some form of sugar while you compete to help you exercise longer and more intensely and recover. Eating fruit is as good or better than drinking sugared fluids, but for some people, eating whole fruit during exercise may cause discomfort from gas or bloating. Experiment and see what works best for you.