Eat Well to Stay Well

How the Right Foods Can Keep Your Immune System in Top Shape

The Power of Carbohydrates

Nieman, himself an avid runner, finds little conclusive evidence that vitamin C, zinc, glutamine or other popular nutritional supplements can influence an immune system suppressed by prolonged, intensive exercise. So he was just as skeptical when he began researching the possibility of boosting immune function by using a carbohydrate beverage during exercise. "I really didn’t think it would work," he says. "I’ve seen these immune system changes occur [as a result of exercise] in study after study and I didn’t think that anything could turn it around."

Following several double-blind placebo-controlled trials (neither Nieman nor the subjects, who included marathon runners, knew who was drinking the carbohydrate-containing beverage) he’s impressed with the results. "In every case, all the athletes on the carbohydrate beverage showed little change in their stress hormones," says Nieman. This suggests these athletes experienced less stress to the immune system than those who received the placebo.

Consuming carbohydrate during exercise appears to boost the immune system by preventing precipitous dips in blood sugar. A low blood sugar level causes the body to release large quantities of stress hormones, particularly cortisol. Typically elevated after prolonged or intense exercise, cortisol profoundly suppresses immune function. In a nutshell: Take sugar in and keep your glucose up during exercise and your cortisol levels will be significantly lower. And that may be the edge you need to keep a cold, sore throat or the flu at bay.

Runners who train or compete frequently for 90 continuous minutes or more—sound like anyone you know?—should benefit the most from consuming carbs on the run. According to Nieman, at 90 minutes "all of a sudden the body’s glycogen stores are getting severely depleted, water is going down if you’re not drinking and your body temperature is going up and your brain starts to interpret all this as stressful. Carbohydrate supplementation really becomes an issue to help counter the negative changes routinely seen in immune function."

Drinking water should be sufficient during training efforts lasting 60 minutes or less. If you’re going longer or tackling a particularly strenuous workout, use a sports beverage or other easily tolerated source of carbohydrate, such as diluted juice or water and an energy gel. Not only will you improve performance by delaying dehydration and maintaining a high blood-sugar level during exercise, you may also lower your risk of falling prey to an infection.