From the None issue of Runner's World
Not so long ago, most Americans didn't know a carbohydrate from a carburetor. But thanks to the popularity of no-carb, low-carb, and selective-carb diets such as Atkins, The Zone, and The South Beach Diet, it seems carbohydrate counting has become our new national pastime.
This great carbohydrate debate has been perplexing for runners, since carbs have long been considered the fuel of choice before, during, and after runs. No need to worry here, though.
Carbohydrates are still the best way to fuel your running.
But all the publicity surrounding carbs has yielded one crucial fact for runners: Not all carbohydrates are created equal. Some provide your body with a slow and steady stream of energy, while others deliver fast but short bursts of fuel. The difference between these two types of carbohydrates is something called the glycemic index (GI).
The GI is a carbohydrate ranking system that assigns a number from 1 to 100 to a food based on how quickly the carbohydrates in it enter your system. If the carbs are quickly digested, with sugar rapidly entering your circulation, the GI is high: 70 plus. Many complex carbohydrates such as breads, pasta, and potatoes have moderate to high GIs.
If your digestive system has to wrestle with the carbs a bit before the sugar makes its way throughout your system, the food's GI is low: less than 55. Most fruits and other fiber-packed foods such as beans and old-fashioned oats have a low GI, because the fiber trips up the sugars before they are absorbed into your system.
The addition of fat or protein also changes a food's GI. Both of these nutrients slow digestion and, therefore, lower the GI of a food or meal. So, a slice of wheat bread topped with peanut butter has a lower GI than the bread alone.
Since you won't see the GI listed on most food labels, check out the chart "Guess the GI" to see the GI of some common foods.
Run By the Numbers
All of the popular weight-loss plans that recognize the difference between low GI and high GI carbohydrates strongly recommend eating low GI foods to maintain your weight and health. But things aren't that easy for runners, who need to include a mix of both high and low GI foods in prerun and postrun meals in order to get maximum performance benefits. That's because high GI foods can help boost speed and aid in recovery, while low GI foods extend endurance. So here's what to eat, when:
Before You Run: Go low here. Studies have shown that eating low GI foods about 2 hours before a workout help maintain steady blood-sugar levels during exercise compared with high GI foods. Therefore, you're able to run longer.
In one study, cyclists were given either a high or a low GI meal a few hours before a hard ride lasting 2 hours. The cyclists were then instructed to pedal all out for as long as they could. Cyclists pedaled almost 60 percent longer after the low GI preexercise meal versus the high GI, and they also maintained higher blood-sugar levels. The researchers attribute this to the slow and steady release of carbohydrates from the low GI meal.
Fruit, old-fashioned oatmeal, and low-fat yogurt are great low GI foods to eat about 2 hours before you run to help sustain you for the long haul. But if you find yourself fueling up just minutes before you hit the road, reach for a higher GI energy bar or sports drink so that the carbs will get into your system faster.
While You Run: Time to get high. Eating high GI foods and beverages during exercise helps boost performance. The quickly digested carbohydrates in sports drinks, gels, and energy bars (most bars have moderate to high GIs) offer an immediate source of sugar for your hard-working muscles. The quick-release carbohydrates also keep you feeling alert, as your brain thrives on sugar for fuel.
After You Run: High GI foods are essential when you're trying to restock your glycogen stores. A study with cyclists demonstrated that eating high GI foods following an exhausting session boosted glycogen stores almost twice as much as equal amounts of low GI foods. So after your runs, fuel up with high GI foods such as potatoes, cereals, or waffles.
