One of the more persistent myths in sports nutrition is the idea that long-acting carbohydrates offer an endurance advantage. This myth is perpetuated by the manufacturers of sports drinks and recovery drinks containing long-acting carbs, who trot out data showing that long-acting carbs provide a more sustained level of blood glucose than fast-acting carbs. Most educated consumers equate steady blood glucose with sustained energy. Manufacturers rely on this association to suggest that, by providing sustained levels of blood glucose, their products containing long-acting carbs also delay fatigue better than products using fast-acting carbs. In fact, just the opposite is true. Here’s why.
Muscles contain a fixed amount of glycogen. When muscle glycogen stores are depleted, exercise performance declines very rapidly. The goal, therefore, is to preserve muscle glycogen as long as possible. In the 1960's, researchers discovered that consuming beverages containing fast-acting carbs did just that. Fast-acting carbs are rapidly absorbed in the GI tract, rapidly transported to muscles cells, and rapidly metabolized to provide energy to working muscles. By providing an instant source of energy, fast-acting carbs preserve muscle glycogen, thereby extending endurance.
Long-acting carbs such as super starches, complex carbs and galactose are absorbed more slowly, and must be metabolically converted to fast-acting sugars before they can be transported to the muscles and used as energy. All this takes time, so the working muscles continue to deplete their limited supplies of muscle glycogen while they wait. The result is faster glycogen depletion and a quicker bonk than when fast-acting carbs are consumed. No study has ever been published showing long acting carbs extend endurance.
Long-acting carbs have their place in the diet of the endurance athlete. But that place is not during and immediately after exercise. Keep this in mind when selecting a sports or recovery drink.