TRAINING CENTER

SUGAR IS THE BEST FUEL

By Robert Portman, PhD

It almost seems heretical to say anything good about sugar. Almost daily we read or hear something new about the evils of sugar. It’s true that sugar consumption is unhealthy in most contexts. But the exercise context is a major exception. Our muscles are highly sophisticated energy-producing factories that evolved over a million years or so. Apparently, the muscles haven’t gotten the memo that sugar is bad, because their preferred source of energy is simple sugars. There is no question that complex carbs provide many health benefits when we are not exercising. However, during exercise the preferred and, in fact, only fuel used by muscles is simple sugars.

In spite of how muscles are hardwired, manufacturers of sports and recovery drinks that contain “long-acting” complex carbohydrates suggest that this class of carbs provides a more sustained level of energy, ultimately providing enhanced endurance. Nothing could be further from the truth. In fact, long-acting or complex carbohydrates actually reduce endurance and fail to deliver additional benefits that simple sugars do.

Our muscles contain a fixed amount of glycogen, and when glycogen stores are depleted, exercise performance declines very rapidly. In the 1960s, researchers at the Human Performance Laboratory at Ball State University showed that when carbohydrates, in the form of simple sugars, are consumed during exercise, there is an improvement in endurance performance. The reason is that simple sugars are rapidly absorbed in the gut, transported into the muscle cell and converted into energy. Providing an instant source of energy with simple sugars preserves muscle glycogen, thereby extending endurance.

On the other hand, long-acting carbs such as super starches, complex carbs and galactose are absorbed more slowly and must be metabolically converted to simple sugars before they can be transported to the muscles and metabolized into energy. This conversion takes time, so working muscles continue to deplete their limited supplies of muscle glycogen. A number of studies have demonstrated this phenomenon. In one study, researchers compared the effect of simple and long acting carbohydrates on endurance performance. They found that subjects consuming the simple sugars had 16% greater endurance than those consuming the long acting carb.

The endurance advantages alone should be reason enough to select a sports or recovery drink that contains simple sugars. But what is often not recognized is that simple sugars also play an important role in hydration. This was first shown in the early studies involving sports drinks. Researchers noted that when simple sugars were added to sodium there was a significant improvement in rehydration. The reason is that simple sugars are rapidly transported from the intestine into the blood. Since simple sugars are small molecules they act similarly to sodium. As they move from the GI tract into the blood, water follows. So simple sugars not only offer an endurance advantage over complex ones, but they offer a hydration advantage as well. The question naturally arises: Is one simple sugar better than another? The answer here is “more is better”. We now know that there are multiple transport systems that carry simple sugars from the GI tract into the blood. Each of these transport systems has a finite capacity. In other words, they can be overloaded. Using a single simple sugar in your sports drink can quickly overwhelm the transport system. But a sports drink that contains two or, optimally, three simple sugars uses multiple transport systems simultaneously and thereby ensures maximum absorption in the GI tract. The faster the total absorption rate, the faster the various sugars can be converted into energy and the greater the preservation of muscle glycogen stores.

The bottom line: Long-acting carbohydrates offer many health benefits, but during and after exercise you should select a sports or recovery drink that contains two or more simple sugars.