A recent study showing that artificial sweeteners may impact diabetes has generated a great deal of media attention. Beverages sweetened with aspartame dominate the beverage category. Many people consume them because they want to reduce or eliminate their consumption of sugar. The researchers found that artificial sweeteners interfere with normal energy metabolism in a manner similar to that seen with diabetes. Laboratory animals fed artificial sweeteners, showed an increase in blood amino acid levels indicative of a greater breakdown of muscle protein for energy.
What does this have to do with endurance exercise? The answer is quite a bit. During exercise, your muscles use glycogen as their primary energy source. When glycogen levels are depleted, you bonk or hit the wall. Muscle glycogen depletion can be delayed by consumption of a sports drink containing carbohydrate, preferably in the form of simple sugars. A sports drink provides a readily available source of energy to working muscles.
However popular media has painted sugar as evil and, not surprisingly, athletes want to reduce their consumption of sugar. This is healthy as a lifestyle (although not necessarily with artificial sweeteners). The exception is nutrition around the exercise interval, the period before, during and immediately after. For longer bouts of low intensity exercise or shorter bouts of medium intensity exercise, a sports drink containing electrolytes will do just fine. However, consuming sugar-free sports drinks during longer bouts of moderate to severe intensity exercise has unexpected consequences on endurance and recovery. The diabetes study provides insight.
When glycogen levels are depleted and there is no available source of simple sugar via a sports drink your muscles begin to break down protein and convert it into energy. This has the following consequences: protein takes longer to metabolize to energy which means you may bonk sooner and breakdown of muscle protein results in a harder recovery since it places more pressure on the muscle’s protein manufacturing apparatus.
That’s why a carb-protein sports drink such as Accelerade or carb-protein gel such as Accel Gel or 2^nd Surge should be the products of choice during exercise. They provide rapid energy in the source of simple sugars, and because they contain protein, they reduce the muscle’s cannibalization of its own protein. This means less muscle damage and a faster recovery, results which have been confirmed in multiple peer-reviewed studies.