Owner's Manual: Thirty Years of Carbo-loading

Improved Endurance & Delayed Fatigue

Thirty years ago, long distance runners added a new tool to their arsenal: an innovative diet technique termed "carbohydrate loading." Scientists in Stockholm had demonstrated that high-carb foods eaten before and during exercise improved endurance and delayed fatigue. The concept was further developed when the role of glycogen was defined in endurance sports.

To prepare, the athletes would exercise strenuously for several days while on a very low-carb diet (less than 10 percent of total calories), a process called "glycogen stripping." This was followed by two or three days of a high-carb diet (90 percent) and minimal exercise. Although it saturated glycogen stores in the liver and muscle, runners were apprehensive on race day because of the restrictions on training, and they often experienced heaviness in their legs, indigestion, hypoglycemia and ketosis. There was also mounting evidence of adverse effects on the kidney and heart functions of older runners.

By the 80s, the practice had taken on a gentler quality known as "tapering." The glycogen depletion phase was eliminated; athletes reduced their training during the week before the event while maintaining a moderate-carb diet.

Soon after, it became apparent that the primary stimulus for glycogen repletion is exercise. Routine training plus three days of high carbs could fill reserves. Or not. Some athletes resorted to "loaf-loading," in which they would carbo-load but not exercise at all during the days preceding the event.

Today, carbohydrate loading has morphed into the common culture of all runners, if not for the competitive edge, then for the camaraderie, as the pre-event "carbo-loading dinner" has become part of the festivities of many marathons.

A question arose, however, during the carbo-loading studies that is echoed by the current fat-loading experiments begun in the early 1980s: Why does one standard diet prescription not work for everybody?

Ongoing research suggests the answer lies in our gender and in the infinitesimal ways we differ genetically. Women store and use glycogen much differently than men, depending on the phase of their menstrual cycles. And our metabolic rates and energy preferences for fat and carbs may be a matter of our genes. "Some people may oxidize more fat than others, and thus may need more fat (or less fat depending on the specific sport) in their diet for optimal nutrient utilization to achieve maximal sports performance," says Dr. Penny Kris-Etherton, co-director of the Center of Excellence in Nutrigenomics at Penn State University.

With the established role of carbohydrates came the marketing of sports drinks. Initially, nutritionists were not advocates, citing lack of benefit (they did encourage athletes to drink milk). By the mid-1980s, they cautiously advised that the drinks be diluted by half to equal no more than 2.5 percent glucose. This was based on the observation that higher concentrations would delay stomach emptying. By 1990, it was demonstrated that once the solution reaches the intestines, water is absorbed more rapidly in the presence of sugar and sodium. By 2000, the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine welcomed sports drinks, stating "Consumption of sport drinks containing carbohydrates and electrolytes during exercise will provide fuel for the muscles, help maintain blood glucose and the thirst mechanism, and decrease the risk of dehydration or hyponatremia."

Competing companies have pumped the golden goose of carbs for products that will convince athletes that victory and personal bests come wrapped in plastic and foil. The Dietary Supplement Health and Education Act of 1994 opened the floodgates for internet sales and retail stores alike by allowing the supplement manufacturers to make claims for enhanced performance without proof, as long as they listed the ingredients and made no claims of preventing, treating, or curing diseases. Energy bars and gels are convenient but contain nothing that you can’t get from ordinary food. Bananas, bagels, packs of honey and sugar candy cost less and are very palatable.

Running is a water-and glycogen-dependent sport. Bill Rodgers, who ran 35 marathons in under 2:15, shares his wisdom: "I think the key ingredient in running and racing is to avoid dehydration. I don’t see the food issue as significant during a race, but before and after. Run forever and eat well!"