Some carbs are digestible while others aren't; some are considered complex, while others are simple; and some contain soluble fiber while others contain insoluble fiber.
However, nearly all carbs we consume are converted into glucose (blood sugar) with the notable exceptions of fiber and glycerin. The basic carbohydrate for human nutrition is the simple sugar glucose, but our bodies also make a complex carbohydrate called glycogen, the storage form of glucose in the muscles and liver.
Some carbs are high in sugar and digest quickly for immediate energy, while others digest slowly and provide a more controlled release of energy. Given these differences, it's important to consider which carbs are the best for different circumstances such as training and racing.
Athletes require carbs during both high- and low-intensity workouts, but carbs are depleted more quickly during intense activity. Depletion of carbs results in fatigue and rapidly declining performance. When glucose runs out, the athlete stops, or "hits the wall," so it's important to replace carbs at every opportunity to avoid this state.
Making the right choice at the right time
Carbohydrates consumed before, during and after workouts are utilized differently. Carbs consumed before activity can top off energy stores and delay fatigue; during activity they help to maintain blood sugar to fuel muscles; and post-workout they aid in recovery and glycogen replenishment.
Simple carbohydrates, or monosaccharides (sugars), are derived naturally from many foods, including glucose, fructose (typically found in fruits and vegetables), galactose (a milk sugar), sucrose (table sugar), lactose (another milk sugar) and maltose (grain sugar). Simple carbs provide a quick boost of glucose to the blood stream. These are often used by endurance athletes to sustain glucose levels for greater periods of time -- they're readily available and digestible.
Complex carbs, or polysaccharides, contain many molecules of connected monosaccharides. Polysaccharides can be either digestible (starch, dextrins and glycogen), or indigestible (cellulose, hemicellulose, pectin, gums and mucilages).
Dietary fiber, a non-digestible carb, is useful because it may lower fat and cholesterol absorption, moderate blood sugar and reduce the risk of colon cancer and heart disease. So, outside of training, focus on eating more complex carbs overall in your diet. Complex carbs are essential for replenishing glycogen and overall athletic performance.
An athlete's ability to store glycogen is determined by conditioning, hydration and the availability of an enzyme (glycogen synthetase) to convert glucose into glycogen. This enzyme is elevated after exercise -- highest within 30 minutes post-exercise, but remains elevated for 24 hours. So eating an adequate amount of complex carbohydrates within this 30-minute window is ideal for glycogen replenishment. Furthemore, adding a small amount of protein to a high-carbohydrate meal or snack will enhance glycogen storage capacity and will also aid in muscle recovery.
Some sports nutrition products use glucose polymers, a type of artificially-formed polysaccharide. These are chains of glucose molecules that are easily separated in the digestive system, providing a boost of glucose efficiently for an athlete.
Using the glycemic index for performance
Measuring the impact of various carbohydrates on blood sugar is a complex process that takes into account how much and how quickly the sugar gets into the bloodstream. The glycemic index (GI) is a measuring system giving a numerical rating to each carbohydrate. The GI can be useful for athletes looking for sustained energy and optimal recovery. The GI further categorizes carbs into "high-glycemic" and "low-glycemic" foods.
Low-glycemic carbs are recommended for sustained energy levels (slower absorption, lowered insulin response) such as fructose (fruit sugar,) whole wheat pasta, galactose (milk sugar,) brown rice, sweet potato, oats, bran products and most vegetables (except carrots, corn and root vegetables.) Low-GI carbs are good for pre-workout meals or snacks. Consuming low-GI carbs prevent premature lowering of blood sugar levels and thus avoid fatigue.
High-GI carbs, like refined sugar (candy), honey, white rice/pasta, bread and most processed foods, are absorbed quickly. High-GI carbs are good during training, and after training they benefit recovery. During high-intensity training your body may have difficulty processing low-GI carbs, so simple sugars provide a quick and ready source of energy. Consuming high-GI carbs within the first 15 minutes to two hours after training is the optimal window in which to replenish depleted muscle glycogen most effectively.
Carbohydrates are the body's main fuel source for exercise, but it's important to choose the right type for optimal performance. Glucose is the main fuel used by the muscles, and the higher the exercise intensity, the greater the reliance on glucose.
Along with the type of carbohydrates, the concentration is also important. Sports nutrition products are specifically designed to provide both simple and complex carbs in optimal concentrations to prevent gastrointestinal distress (cramps), so consuming carbohydrate-containing beverages during exercise is wise.
If carbs aren't available, the body will burn protein instead; a much slower process. And more importantly, burning protein takes protein away from its normal role of building and repairing muscle tissue. So, supplying the body with an appropriate amount of carbohydrates will prevent the unnecessary breakdown of protein (muscle.)
Ilana Katz has a masters degree in dietetics with an emphasis in sports nutrition. She enjoys working with athletes from the elite to recreational. She specializes in body composition and weight management specific to individual goals and needs. Ilana, herself participates in many endurance and team events in order to relate personally to her clientele. Ilana is The Sport Factory's head nutritionist, has worked with many local celebrities, and is the founder of the nutrition program IndiFITualize. You may hear Ilana on the "Bert" radio show (Q100) as well as "Dave FM" in Atlanta