Paying attention to the glycemic index may be a positive foryour performance.

At first glance, using the glycemic index might sound likeanother nutritional phenomena that could be shelved next to the Zone Diet,Atkins or South Beach. However, before you nix this nutrition guideline andcatalogue it with the list of growing diet trends and passing food faux pas,take another look at what’s on the menu and how you as an athlete can benefit.

The Facts

The glycemic index (GI) is a scale that ranks the effect of glucoseon your body by measuring how fast it raises your blood sugar level and assignsit a number (0-100). While the index was originally designed for diabetics,sports nutritionists found they could gauge a food’s GI effects on athletes.

“Athletes commonly eat foods solo, a banana, a bagel,” saysBoston-based Nancy Clark, MS, RD, CSSD and author of Nancy Clark’s SportsNutrition Guidebook. “Hence exercise scientists became curious about thepossibility that quick or slow carbs impact exercise performance because theyaffect blood glucose in different ways.”

These findings helped establish the glycemic index as auseful tool for maximizing energy levels during exercise by indicating what toconsume at what time. Some foods, like white bread, are known to quickly raiseGI levels, while others, like lentils, are known to maintain low blood sugarlevels. Translation: your GI level could very likely affect your athleticperformance. So how do you know when to eat what, and why?

The Logistics            

Eric Hörst, climbing-training expert and author of TrainingFor Climbing and Conditioning For Climbers, says a good rule of thumb is toconsume “low- and mid-GI foods before and during climbing/training, then highGI foods immediately afterwards (to speed recovery), followed by a taper backto mid- and low-GI foods” if another workout is scheduled within 24 hours.

This kind of glycogen loading is especially important forendurance sports and those with rigorous daily training schedules to maintainconsistent energy long before you mount your bike, tie in for a climb or ejectthe start line of a race.

“The consumption of carbohydrates in the hour beforeexercise can help increase glycogen stores and raise blood glucose and insulinlevels,” says John Ivy, exercise physiologist at the University of Texas andauthor of The Performance Zone, and it “will help jump-start the fuelingprocess.”

Consuming low-GI foods prior to exercise will help youmaximize this energy. Some athletes, however, might be sensitive to certainfoods. Clark suggests you “go by what feels good for your stomach.”

“Continue to consume low- to mid-GI carbs during exercise,”says Hörst—like a sports drink, gel, or granola bar—to keep a steady flow ofnutrients and energy and help maintain the stores. According to Ivy, by doingthis, “there is less likelihood of having a rebound hypoglycemic response.”

Unlike low-GI foods, high-GI foods will spike your bloodsugar; the higher the GI levels, the quicker they raise blood-sugar levels.When blood-sugar levels are spiked the athlete might at first experience a joltof energy, but that will undoubtedly be followed by “hitting the wall” or“bonking” when energy levels drastically drop.

While it’s not advised to eat high-GI foods before aworkout, at the end of a workout it’s important to replenish the muscles asquickly as possible during a 45-minute time period after intense exercise knownas the “glycogen window.”

According to Ivy, intense exercise quickly uses up muscleglycogen stores, and it’s “important to replenish muscle glycogen as fast aspossible.” Ivy suggests trying “a supplement of carbohydrates (high glycemic)plus protein. It will increase muscle glycogen synthesis faster thancarbohydrates alone…and will limit muscle tissue breakdown that occurs withhard exercise.”

Bob Seebohar, MS, RD, CSSD, CSCS and sports dietician at theU.S. Olympic Committee, has been working with athletes for the past 10 years.He says it “somewhat depends on the sport and the specific energy systems used,but in general, having ‘slower burning’ (lower GI) fuel before a competition ortraining session is a benefit to almost any athlete, while ‘faster burning’(higher GI) fuel during a competition or training session is beneficial inorder to maintain blood sugar and prevent hypoglycemia.”

Is the Glycemic Index for Everyone? 

While many athletes adhere faithfully to the parameters ofthe glycemic index while training, some believe that what works in theorydoesn’t always translate. Clark suggests that there are too many grey areas andvariables in the glycemic index, and claims it’s a “false scale.” How much youeat, the food’s preparation, hot or cold, and where it was grown are only a fewof the things that factor in when determining GI. What’s more, response tocarbs can vary not only from person to person, but throughout the day. “It’sbetter to experiment with different foods,” says Clark, and then decide whatworks for you.

In the end, diet choices are yours. The GI rating can createa good guideline to follow, but ultimately you’re the boss of what goes intoyour  body.