Use the glucose index--a measure of how carbs affect your blood sugar--to get the energy you need during a workout and enhance your training
As an endurance athlete, you already know how important carbohydrates are to performance. Carbs provide the fuel for your body as well as your brain-they are digested and turned into blood glucose to be used immediately, or stored in your muscles as glycogen for later use.

In recent years, there's been increased interest in exactly what kinds of carbs are best for your health. Diets like The South Beach Diet are based on cutting out high GI foods and relying on lower GI options to encourage weight loss.

But the GI can help competitive and recreational athletes as well. Read on for how eating the right GI foods can improve your workouts:

THE BASICS OF THE GI
"The GI is actually a chart or formula that's based on the effect of 50 grams of carbohydrates ... and how eating that 50 grams of carbohydrates affects your blood glucose levels," explains registered dietitian and American Dietetic spokesperson David W. Grotto, RD, LDN, author of 101 Foods That Could Save Your Life.

The GI assigns a value of "100" to 50 grams of pure glucose. Other foods are ranked from 0 to 100 depending on their effect on blood sugar levels.

The GI was first developed to help people with diabetes get better control over their blood sugar by creating an easy-to-understand ranking system for carbohydrates. The higher the GI, the higher the increase in your blood sugar level. Lower GI foods take longer to digest, causing less of a spike on blood sugar and insulin levels.

Here's the thing: carbs, regardless of type, are digested more quickly than protein and fat. However, lower GI foods are digested more gradually, which means your body need not produce as much insulin at one time. High GI foods, on the other hand, create an accompanying need for a lot of insulin all at once. The problem is that high GI foods also tend to create an accompanying rapid drop in blood sugar-and the excess insulin in your system can leave you feeling tired, cranky or irritable. Worse yet, if you're on a run or a ride, that blood sugar plummet makes you likely to bonk.

HIGH VERSUS LOW GI
But high GI foods aren't all bad. Consuming high GI foods like energy drinks or bananas during a demanding workout can help provide the energy your body needs. After a demanding workout, eating high GI foods will help you restore your muscle glycogen stores more efficiently. "If you are an athlete, you need that quick, available blood glucose-not only for pre-event-but also for post-recovery," says Grotto. "High GI foods improve your body's ability to get the glucose into the muscle cells to build up the glycogen." Aim for high GI foods within 60 to 90 minutes after a hard workout to replenish your glycogen stores. Bagels, rice and potatoes are all good sources.

During the day, though, you're better off eating lower GI foods as part of your regular diet. Endurance athlete Ted Kotuzis, MD, has discovered this firsthand. The 40-year-old St. Charles resident has been doing triathlons since 1989 and has competed in distances from sprint to Ironman. Over time, he learned that eating low GI foods throughout the day helps him maintain consistent energy levels. "Eating low-GI foods ... helps maintain a normal [blood sugar] range and minimize insulin spikes as much as possible," he says.

Kotuzis qualified for the World Championships 70.3 in Clearwater in November. He currently trains about 15 hours a week. While he avoids high GI foods during his workday, he uses them during endurance workouts and immediately after to replenish his glycogen stores.

"After coming in from a race, a hard workout or a brick or something of that nature ... the quicker you can replenish your glycogen stores, the better," says Kotuzis. "To me, the most important thing is every meal has to set up the next workout ... so your glycogen stores have to be topped off ... As an endurance triathlete, the most important meal is the meal immediately after the workout."

BLENDING BOTH FOR TRAINING SUCCESS
Athletes should use both high and low GI foods to maximize their training, says Grotto. "Athletes need something for an immediate boost of energy, but they also need things that will help sustain them for longer runs, so they need those slower burning carbohydrates," he says.

In fact, some research suggests that eating lower GI foods before exercise may increase the amount of time people are able to exercise. In one study, college-aged men who ate a moderate GI meal 45 minutes before exercising on recumbent bicycles were able to draw more glycogen from their liver stores during the last half-hour of exercise than the men who ate a high GI meal. This enabled them to exercise at 60 percent of their aerobic capacity for a slightly longer period of time. While several other small studies have produced similar results, other research has found that consuming low GI foods instead of high ones before exercise has no effect on athletic performance.

LIMITATIONS TO THE GI
Everyone's body is different, so your response to a GI food may be different than your training partner's. Other factors that affect your body's response to a carbohydrate food include how much of it you eat, the way the food is cooked, what you eat with it, the amount of fiber it contains and the type of starch or sugar the food contains.

"There are intrinsic and extrinsic factors that affect your blood glucose, so it's not only the GI," says Grotto, who's based in Elmhurst. "You could have a high GI food, but if you're pairing it with something that contains fiber or protein or fat, that can actually lower the glycemic effect."

Recognizing that portion size can significantly affects a food's impact on blood glucose, researchers now are focusing more on glycemic load, or GL, which also takes into account the normal portion size of a particular food. (To calculate a food's GL, multiply its GI by the number of grams the portion contains and divide by 100.) Remember that portion size affects blood glucose, too.

So, what's the take-away message? To stabilize your energy during the day-and have enough left over to train hard-incorporate more low-GI foods into your diet. Consuming high GI foods immediately after a workout, though, will help you recover more quickly and set up you up for your next training session.

Kelly James-Enger is a freelance health and fitness writer from Downers Grove. www.becomebodywise.com.