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Carbohydrates for Endurance Athletes

Why are carbohydrates so important for endurance athletes?


         Recently, carbohydrates have received a bad rap for no good reason! Yes, consuming large amounts of highly processed carbohydrates is not recommended. Refined carbohydrates have been stripped of most of their nutrients and have very little to offer the body in terms of health benefits. However, that doesn’t mean carbohydrate sources, such as whole grains, fruits, and vegetables are unhealthy. Most whole food carbohydrates also contain many vitamins and minerals, crucial for many physiological processes in the body. Fruits, vegetables, and whole grains also contain fiber, an important nutrient for intestinal health and satiety following a meal.

         The problem, and reason why carbohydrates are often labeled unhealthy, is that the majority of carbohydrates consumed by Americans is in the form of highly processed foods. Theses energy-dense food sources , such as soda, pre-packaged cookies and crackers, pastries, etc, offer little to the body besides calories. Thus, they are sometimes referred to as empty calories. Also, pre-packaged foods are often high in saturated fat, making them an even more undesirable choice to consume in large quantities.


So why consume carbohydrates then?


         During exercise, carbohydrates are the body’s main source of fuel. At higher intensities, the energy demand by the muscles significantly increases and reliance on carbohydrates becomes even greater.  

Also, research studies have consistently shown improved performance when carbohydrate is consumed both before and during endurance competitions (Cox et al., 2010; Rodriguez et al., 2009).

         Post-exercise, carbohydrates are also important to consume because they help promote recovery. During exercise, muscle glycogen (body’s storage form of carbohydrate) is broken down and used to fuel muscle contractions. Post-exercise, re-synthesis of glycogen is important for recovery and priming the body for future sessions or competitions. If adequate carbohydrate is available, glycogen re-synthesis is rapid and recovery in enhanced. If carbohydrate is not available, glycogen re-synthesis is delayed and recovery is hindered. This can affect future exercise sessions, and result in a vicious cycle of lowered glycogen followed by incomplete glycogen re-synthesis. Chronically, this cause fatigue and can lead to overtraining syndrome.

         Also, the brain requires 130g carbohydrates each day as a minimum to stay alive! If carbohydrates are not available, the body can convert fat and protein to produce ketone bodies, a form of energy the brain is able to use. Keytone bodies can serve as a temporary energy source, but can induce a state of ketosis, lowering the pH of the blood. For endurance athletes, chronic use of ketone bodies is not advised because it can be detrimental to performance, especially at higher intensities.



So why then do some people recommend limiting carbohydrates?


         For the average American, reducing the total amount of energy consumed each day is important for weight loss and lowering risk for chronic diseases. Pre-packaged carbohydrate sources are readily available, and many Americans over consume these highly processed, energy dense, foods. Since there is little nutritional value associated with foods such as soda and packaged snacks, and most are high in calories, sugar, and saturated fat; limiting these types of carbohydrates is recommended.

         The goals, however, of an individual trying to lose weight and an athlete trying to improve fitness are very different. Weight loss and improving fitness are at opposite ends of the spectrum. For weight loss to occur, energy intake must be lower than energy expenditure. To improve athletic performance and fitness, energy intake should equal energy expenditure. In a way, an athlete must be much more conscious of food intake to ensure they get enough of each nutrient to improve fitness and enhance recovery. 

         There will always be people who claim they have discovered the ‘optimal food’ or ‘magic diet’ that will improve performance or enhance weight loss. These claims however, are rarely backed up by scientific evidence. Often times the results of a scientific study are taken out of context, and recommendations don’t match the evidence. Unfortunately, these claims often receive a lot of media attention, leaving the consumer to determine the validity of such information. As a consumer it can be confusing to determine the truth when conflicting information is presented. The best approach to take is to critically examine the information. Where is it coming from? What’s the scientific evidence? Is this a reliable source? Does it sound too good to be true? In the words of a recent scientific letter addressing a controversial statement made by a couple authors:

“Turning consensus into controversy does NOT enhance science…..”

         -B Murrary, Br J Sports Med 2007;41:106-7.



Want to learn more? Check out these sources:


Cox GR, Clark SA, Cox, AJ, Halson SL, Hargreaves M, Hawley JA, Jeacocke N, Snow RJ, Yeo WK, Burke LM. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance exercise. J Appl Physiol 2010;109(1):126-34.


Murray B. Manufactured arguments: turning consensus into controversy does not advance science. Br J Sports Med 2007;41:106-7.


Perrot AA, Clifton P, Brauns F. Low-carbohydrate diets: nutritional and physiological aspects. Obesity Rev 2006;7(1):49-58.


Rodriguez NR, DiMarco NM, Langley S. Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Am Diet Assoc 2009;109(3):509-27.