The practice of carbo-loading dates back to the late 1960s. The first carbo-loading protocol was developed by a Swedish physiologist named Gunvar Ahlborg after he discovered a positive relationship between the amount of glycogen (carbs stored in the muscles and liver) in the body and endurance performance.
Scientists and runners had already known for some time that eating a high-carbohydrate diet in the days preceding a long race enhances performance, but no one knew exactly why until Ahlborg's team zeroed in on the glycogen connection.
Subsequently, Ahlborg discovered that the muscles and liver are able to store above-normal amounts of glycogen when high levels of carbohydrate consumption are preceded by severe glycogen depletion. The most obvious way to deplete the muscles of glycogen is to eat extremely small amounts of carbohydrate. A second way is to engage in exhaustive exercise.
The stress of severe glycogen depletion triggers an adaptive response by which the body reduces the amount of dietary carbohydrate that it converts to fat and stores, and increases the amount of carbohydrate that it stores in the liver and muscles as glycogen.
Ahlborg referred to this phenomenon as glycogen supercompensation. Armed with this knowledge, he was able to create a more sophisticated carbo-loading protocol than the primitive existing method, which was, more or less, eating a big bowl of spaghetti.
The Ahlborg Method
Ahlborg came up with a seven-day carbo-loading plan in which an exhaustive bout of exercise was followed by three or four days of extremely low carbohydrate intake (10 percent of total calories) and then three or four days of extremely high carbohydrate intake (90 percent of total calories).
- Perform an exhaustive workout one week before a long race (90 minutes-plus).
- Consume a very low-carb diet (10%) for the next 3-4 days while training lightly.
- Consume a very high-carb diet (90%) the next 3-4 days while continuing to train lightly.
Trained athletes who used this protocol in an experiment were able to nearly double their glycogen stores and exhibited significantly greater endurance in exercise lasting longer than 90 minutes.
After these results were published, endurance athletes across the globe began to use Ahlborg's carbo-loading plan prior to events anticipated to last 90 minutes or longer. While it worked admirably, it had its share of drawbacks.
First of all, many athletes weren't keen on performing an exhaustive workout just a week before a big race, as the plan required. Second, maintaining a 10 percent carbohydrate diet for three or four days carried some nasty consequences including lethargy, cravings, irritability, lack of concentration and increased susceptibility to illness. Many runners and other athletes found it just wasn't worth it.