Basics of Carb-Loading for Sports Performance

By Christopher Solga, MS, RDN
Runner Checking Time - Using Carbohydrate Loading for Performance

Maridav/iStock/Thinkstock

Ask any endurance athlete what is the most important food to eat before a race and they will respond, "Carbs!" Carbohydrates are the primary fuel source burned for energy during physical activity, and our bodies are able to store some of the carbohydrates we eat in our liver and muscles as glycogen.

It makes sense that eating carbohydrate-rich foods to maximize our glycogen stores — a strategy known as carbohydrate loading — provides athletes with the energy necessary to sustain an increased level of physical activity for a longer duration. For example, an athlete can store 1,800 to 2,000 calories of fuel as glycogen in the muscles and liver. This energy can fuel about 90 to 120 minutes of vigorous activity. More recent evidence suggests that in events lasting longer than 90 minutes, maximized glycogen stores can improve a runner's finish time by 2 to 3 percent. This could translate to a 5- to 7-minute improvement for a 4-hour marathoner.

The concept of carbohydrate loading has been studied for decades. But, how did this theory hold up in the real world? One of the first recorded instances of a professional athlete using carbohydrate loading in competition was during the marathon event of the 1969 European Athletics Championships. British runner Ron Hill, trailing the leader for most of the race, was able to win the gold medal with a strong finish in the final six miles, the point at which many runners experience the phenomenon known as "hitting the wall" — the feeling you get when your glycogen stores are depleted and your physical performance nosedives. Word of Hill's diet spread and athletes have been attending pasta dinners the night before an event ever since — although, true carbohydrate loading is more involved.

Hill followed a classic carbohydrate-loading regimen consisting of a glycogen-depleting phase — three days of intense exercise coupled with very-low carbohydrate consumption — followed by three days of tapered physical activity with high-carbohydrate intake. This strategy, however, may not be optimal for all athletes and unnecessarily increase the risk of injury while training in a depleted state. Some studies even show that trained athletes can achieve maximized glycogen stores without the need for a depletion phase in as little as 24 hours.

Eating a high-carbohydrate diet may help athletes perform at their best. The amount of carbohydrates that athletes should consume daily will depend on their unique needs, the athletic event and training regimen. Eating an unusually high amount of carbohydrates before an event could actually backfire and hinder athletic performance by causing gastrointestinal distress. The foods eaten immediately prior to an event should be the same foods eaten during training.

The golden rule of sports nutrition — nothing new on race day — also applies to carbohydrate loading. Athletes should consider consulting a registered dietitian nutritionist for personalized nutrition guidance.

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