Ask the Experts: Proper Fueling

Fueling during a long exercise enhances performance.

I'm training for my first marathon. I've heard I'll need to eat during long runs and the race and that I should try energy gels. Why are gels better than solid food?

Years of research have shown that consuming carbohydrates during an endurance effort, such as a marathon, improves performance by maintaining blood, liver and brain glucose--which the body metabolizes into energy--and by sparing muscle glycogen, or stored glucose--which delays fatigue. Selecting carbohydrates that are easy to digest is key to getting fuel to muscles quickly, while also avoiding stomach distress. Energy gels are easy to ingest, digest and absorb.

Not so for solid food. Eating solid food not only requires chewing, which can be difficult "on the run" and even cause choking. It is also harder for your body to digest quickly, meaning you don't have fast access to the energy you need. What's more, a large amount of blood is directed to your working muscles and skin (for sweating and maintaining body temperature) instead of to your gut, making digestion more difficult.

Consuming gels or drinks with up to 75 grams of an optimum blend of carbohydrates during each hour of exercise will maintain desired levels of blood and brain glucose and spare muscle and liver glycogen. The combination of maltodextrin (a type of glucose) and a small, but significant, amount of fructose (fruit sugar) allows for optimum fuel absorption during endurance exercise.

Other beneficial ingredients in gels are branched chain amino acids or BCAAs (leucine, valine and isoleucine), antioxidants (vitamin C and E), herbs (chamomile, ginger) and caffeine (see question 3). Replenishing BCAAs, the building blocks of protein, aids in athletic performance and recovery. Combined with carbohydrates, they help sustain energy and reduce exercise-induced muscle damage.

Just as you prepare your body to run the distance through training, you also need to hone a nutrition strategy (what you consume and how often) through practice. During training runs, test different brands and flavors to discover what works best. Never try anything new on race day.

When do I need a sports drink instead of just water? What ingredients should I look for?

For moderate exercise lasting less than an hour, water should be fine. However, for longer and more intense efforts, you'll benefit from a sports drink. Unlike water, sports drinks contain electrolytes and carbohydrates to enhance fluid absorption and retention, and help maintain energy. Sports drinks do a better job of preventing dehydration and maintaining proper electrolyte balance, especially in warm, humid conditions when you sweat out more fluid and sodium. Replenishing sodium enhances fluid absorption and retention and prevents hyponatremia, when blood sodium concentration falls below normal, which in extreme instances can be deadly.

Properly formulated carbohydrate-electrolyte drinks allow for optimum exercise performance. Science confirms that a combination of water, carbohydrates, sodium, a little potassium and some flavor for palatability makes the optimal drink formula. Since you can sweat out significant amounts of sodium during exercise, look for a sports drink that contains at least 500 to 700 milligrams (mg) of sodium per liter. Also select one you don't have to dilute due to sweetness or overpowering flavor because you'll dilute the electrolyte and carbohydrate concentration as well.

Most experts recommend replenishing fluids according to your sweat rate, how much fluid you lose in one hour of relatively intense exercise. Weigh yourself naked before and after an hour's run at race pace, and drink the same amount you lost. For example, if you lose two pounds during one hour of running, you need to replace about 32 ounces (two pounds) of fluid during each hour of exercise. If you're consuming more than that, you're probably over-hydrating. To avoid guzzling too much at one time, drink fluids in small amounts at regular intervals, every 15 to 20 minutes. Drinking about 16 ounces of sports drink one to two hours before an event will also help maintain adequate hydration.

It seems more sports drinks and energy gels contain caffeine, but doesn't caffeine have a dehydrating effect? How does caffeine improve performance?

The amount of caffeine in most energy gels and sports drinks on the market is relatively low in regards to its dehydrating effects. For example, one study on a 132-pound athlete who consumed 300 mg of caffeine found no significant dehydration. To give some perspective, an average cup of coffee contains approximately 120 mg of caffeine, and most gels have anywhere from 20 to 40 mg per packet.

But caffeine has been shown to improve performance by reducing the rate of muscle glycogen consumption and making strenuous efforts feel easier. Consuming caffeine before and during exercise leads to a breakdown of stored fat, bringing more free fatty acids into the bloodstream where they can more easily be used for energy, thereby sparing muscle glycogen. As a result, exercise is prolonged and fatigue is delayed.

Caffeine also is well known for its stimulant effect on the central nervous system. Studies have shown that caffeine increases the release of adrenaline, the "fight-or-flight" hormone, giving the body a boost and increasing alertness and concentration.

But athletes participating in sports that require mastering precise patterns of movement, such as throwing a shot put or discus, wouldn't benefit from caffeine the way a runner or cyclist, who depend more on stamina than precision, may. The possible side effects of caffeine intake, including the jitters, would negatively affect performance in sports where one jerk of the hand may make the difference in a winning throw. However, the benefits of caffeine--alertness, focus and a perception of less effort--can help an endurance athlete across the finish line.

Bear in mind, in the case of caffeine, more is not better. More caffeine intake does not correlate with better performance and, in fact, could be a detriment. One study showed that when comparing exercise time to exhaustion in athletes who took varying amounts of caffeine one hour before the start of exercise, those who took the least amount of caffeine (3 mg per kilogram of body weight or almost 180 mg of caffeine for a 130-pound person) were able to exercise longest. With only 20 to 40 mgs of caffeine, energy gels don't have enough caffeine to make you tired once they wear off.

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Former NCAA All-American and cross-country coach, Magdalena Lewy, M.S., is director of Research and Development for GUsports. She's an elite marathoner who finished fifth at the 2004 U.S. Olympic Trials with a PR of 2:30.

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