The role of carbohydrates in the body includes providing energy for working muscles, providing fuel for the central nervous system, enabling fat metabolism, and preventing protein from being used as energy. That said, carbohydrates are the “preferred” source of energy or fuel for muscle contraction and biologic work.
Major food groups that contain carbohydrates are grains, fruits, and milk products. Vegetables have a small amount of carbohydrates, but can contribute to the body’s carbohydrate level, depending upon how much is eaten.
How do carbohydrates really work in the body? After carbohydrates are eaten, they are broken down into smaller units of sugar (glucose, fructose, and galactose) in the stomach and small intestine. These small units are absorbed in the small intestine and then enter the bloodstream where they travel to the liver. Fructose and galactose are further converted to glucose in the liver. Glucose is the form of carbohydrate that is transported by the bloodstream in the various tissues and organs, including the brain, where it is used as energy throughout the body.
The important factors relating to our understanding about the use of carbohydrates in the body, is the that if the body does not need glucose for energy right away, the body will store glucose in the liver and muscles in a form called glycogen. This storage form is used by the body for energy when the body needs more glucose that is readily available in the bloodstream, for example after exercise. The body does have limited storage capacity for glycogen (about 2000 calories), which is why carbohydrates are commonly referred to as a limited fuel for physical performance.
One other factor that you may want to remember about carbohydrates is that it will spare protein as an energy source in the body. This is an important factor for our exercise planning because when carbohydrate consumption is inadequate and protein is broken down, we lose our primary source of building blocks for muscle development. Further, protein breakdown may result in an increased stress on the kidneys, through which protein byproducts are excreted.
Glucose is also an essential for the central nervous system. The brain primarily uses glucose as its energy source, and a lack of glucose can result in weakness, dizziness, and low blood sugar, or hypoglycemia. Reduced blood sugar during exercise decreases performance and could lead to mental, as well as physical fatigue.
These factors, while they play out day after day in our body, need to be remembered when making choices for support foods, before or during exercise, and even for all daily activities, where we want to be at our best.
The carbohydrate levels you maintain in your body will be based on caloric needs for your day; that is, how fast you burn your calories and the physical demands on you for the day’s energy needs. Concentrating on carbohydrate needs being adequate can vary from day to day. Some “normal” days you may need 35% of calories as carbohydrates, and other days you may need more—50-60% of calories—for more intense physical activity. You will learn just by practice how much carbohydrate you need by the way you feel during and after physical activity. And, learning what you need will bring increased satisfaction with your body function and resulting energy usage when needed.
Coming up, we will look at the actual breakdown of carbohydrates in your body and its timing for use, and see if you can plan to eat according to your energy needs at the time!
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Written by Rita Larsen, RDN, CD; Elite Sports Clubs Nutrition Educator & Diet Counselor
Rita is certified in Positive Psychology, University of Penn; has a BS in Dietetics from Kansas State University; and an Internship and Masters at the Indiana University Medical Center.