Carbohydrates Fuel Athletic Performance

By Nancy Brinch, MS, RD, LSW

You've seen the ads touting low carbohydrate diets such as Dr Atkins' New Diet Revolution or Protein Power. Proclaiming that carbs make us fat, these diets shun pasta, bread, potatoes, rice, cereals, and fruit in the name of weight reduction. It's the anecdotal reports of astounding weight loss from proponents of these diets that lures people into following this approach. Their hope is to lose weight while eating unlimited quantities of their favorite foods.

Should athletes follow the low carbohydrate trend?

The issue of incorporating carbohydrates in the diet is especially critical for athletes seeking an edge to improve their performance. Let's start with some basic facts:

•Carbohydrates are the body's main source of energy and the only source of energy for the brain and the nervous system.

•Carbohydrates spare protein so it can be used to build and repair muscles and make enzymes, hormones and antibodies rather than being used to fuel our bodies.

•Carbohydrates are essential for fat metabolism. Without sufficient carbohydrate fat cannot be burned completely.

•Carbohydrates are stored in our muscles and liver to be used as energy between meals and snacks. This storage of carbohydrate is essential for athletic performance.

Because carbohydrate (in the form of glucose) is absolutely essential for the brain and the nervous system, the body goes to great lengths to maintain an adequate blood glucose level. If the blood glucose falls too low we experience signs such as hunger, dizziness, shakiness, weakness, rapid heartbeat, and anxiety. Obviously these symptoms can seriously impair athletic performance. To avoid this, the body stores glucose in the form of glycogen in the liver. This liver glycogen can be broken down to glucose and released into the blood whenever the blood sugar level falls too low. Glycogen is also stored in the muscles to fuel muscle contraction. The amount of glycogen stored in muscles can be a limiting factor for athletic performance. If the muscle glycogen becomes depleted due either to a low carbohydrate intake or exercise, muscles cannot function at peak level. In this scenario protein becomes a source of glucose because some of the building blocks of protein can be converted to glucose. When this occurs lean muscles tissue is lost.

The bottom line:
If you don't have enough carbohydrates in your diet you won't be able to continue doing high intensity activities. What are the best sources of carbohydrates for athletic performance? The answer depends on the timing of carbohydrate intake. During exercise and immediately afterward carbohydrates that are quickly digested and absorbed are the best choices. They provide a source of glucose to fuel exercise and to replenish glycogen stores after exercise. These so-called "high glycemic index" carbohydrates include foods such as most breads (i.e. white bread), most breakfast cereals (i.e. cornflakes), sports drinks, white potatoes, and sodas. Before exercise, eating low or moderate glycemic index carbohydrates provides a sustained level of blood glucose. This even level of blood glucose enhances athletic performance. These carbohydrate foods include juice, most fruits (i.e. apple, orange, banana), rice, yogurt, milk, oatmeal, chickpeas, lentils, kidney beans, most pastas, muffins, crackers and most cookies.

The recommended amount of carbohydrate for athletes is 3 or 4 grams of carbohydrate per pound of body weight per day. Higher levels are required during periods of intensive exercise. Nutrition labels are a good source of information on carbohydrate content of foods. Another source is the USDA National Nutrient Data Base at www.nal.usda.gov/fnic/foodcomp/.