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Carbohydrates: The Power Nutrient

Carbohydrates: The Power Nutrient

Building Blocks

There is no need to fear the c-word! Carbohydrates are the body’s primary source of energy, and the brain relies exclusively on them. The majority of calories in an athlete’s diet should be coming from healthy sources of carbohydrates. The most important thing is to be able to identify which carbs are healthy and to know when and how much to eat. 

The building blocks of carbohydrates are monosaccharides (glucose, fructose, and galactose) and disaccharides (maltose, lactose and sucrose).  These are commonly referred to as “simple” carbohydrates. “Complex” carbohydrates are formed when three or more glucose molecules combine. Polysaccharides (10 or more glucose molecules) are very common in the diet. Simple and complex carbs have different digestion times, and both types can play a role when incorporated into the athlete’s diet.

Function of Carbohydrates

The primary function of carbohydrates is to supply energy – energy for the brain and working muscles. Along with fat, carbohydrates provide most of the energy for the body to function,  The level, length and intensity of activity determines whether carbohydrate or fat will be used preferentially.  For example at rest, 15-20% of muscle energy comes from fat but during intense exercise (greater than 85% VO2 max) carbs are responsible for the majority of energy production. Ideally, calorie and macronutrient intake are appropriate and what the body needs is readily available for energy production. If intake is falling short and carbohydrate needs are not being met, the body must work harder to convert other nutrients to glucose for ATP production.

When carbohydrates are consumed, some are used immediately, and the rest are stored for later use in the form of glycogen. The two storage sites for glycogen are muscle and liver cells. For a typical sedentary adult, the liver can store approximately 300-400 calories, and the muscle can store 1200-1600 calories. Training can increase these stores, allowing for additional energy storage and under normal conditions, a very small amount of glucose (about 20 calories) can also be found in the blood. When energy is needed, metabolic processes mobilize glycogen to produce ATP and give the body fuel.

Glycogen: Storage form of glucose found in the liver and muscle

Carbs in the Athlete’s Diet

Sources of carbohydrates include fruits, vegetables, grains and sweets. Foods like beans and dairy products also contain some carbohydrates. Fruits, vegetables, whole grains and beans also contain fiber, a form of complex carbohydrate that takes longer to digest.

When making any food choice, athletes need to consider a few basic principles:

  • Taste preference – simply choose foods that are pleasing to personal taste
  • Nutrient density – mostly choose foods with a high amount of nutrients (see section 2)
  • Digestion time – how long will this food take to digest before activity
  • Personal tolerance – individuals digest differently. Athletes need to choose food they know they can digest without a problem (there might be some trial and error involved).

For meals, athletes generally want to choose nutrient-dense carbs like whole grains, fruits and vegetables. Beans and dairy products will also provide some protein along with carbohydrate. Many of these foods tend to be high in fiber as well, which helps keep the digestive system healthy. Some high fiber foods can cause stomach upset, so it is important for athletes to be aware of what they can digest comfortably, being careful not to consume too many high fiber foods when they need to be active.

When and How Much

In the athlete’s diet, approximately 45-65% of total calories should come from carbs, depending on the athlete and type of sport. Linemen, for example, would be on the lower end of that spectrum, while marathon runners would be on the higher end.  Before an activity, carbs are needed to provide energy to fuel the workout and after exercise (along with protein) to replace stores that have been depleted. The Academy of Nutrition and Dietetics recommendation for carb intake ranges from 6 to 10 grams per kilogram body weight (2.7 to 4.5 grams per pound) per day.  If an athlete has 3 to 4 hours before being active, they should plan to have a well-balanced meal with all macronutrients represented. As activity approaches, they want to adjust their intake to fuel properly for the upcoming workout.


One to two hours before activity, athletes want to choose mostly easily digestible carbohydrates. Since carbs are usually digested more quickly than protein and fat, this 60-120 minute window allows enough time for the food to be digested and its energy available to fuel activity. Good choices pre-workout can be fresh or dried fruit, pretzels, crackers, low-fat granola bars, nonfat yogurt and sports drinks.


There may not be a need for fuel during activity. Short workouts and many team sports do not require additional fuel if pre-event nutrition needs have been met. On the other hand, long duration activities such as tournament play and endurance events (marathons, long-distance cycling, triathlons, iron man competitions, etc.) require additional calories. For the most part, athletes want the same type of quick and easily digestible carbs during this time. Sports drinks, gels, or dried fruit are all useful options. 


After exercise glycogen stores need to be replenished and fatigued muscles need to recover. Athletes should start replacing carbohydrate stores within 30 to 60 minutes post-exercise when muscle cells are most sensitive. Carbohydrate intake recommendations are 1.0 to 1.5 grams per kilogram (0.5 to 0.7 grams per pound) body weight during the first 30 minutes and again every two hours for 4 to 6 hours. Depending on the athlete’s schedule, this can be achieved through a series of small meals and snacks. Along with carbohydrate is a need for protein, which will be discussed further in section 4.


  • Carbohydrates are the body’s primary source of energy
  • Sources include whole grains, fruits, vegetables, sweets, beans and dairy
  • Daily needs are 6-10 grams per kilogram body weight
  • Athletes should choose easily digestible carbs before activity
  • Post workout needs for glycogen replenishment and muscle recovery
    • 1 to 1.5 grams per kilogram within 30 minutes and again every 2 hours for 4 to 6 hours along with adequate protein intake.

The NESTA Sports Nutrition Specialist course is designed for personal fitness trainers, strength coaches and nutrition experts who want to learn cutting-edge techniques for increasing sports performance, reducing recovery time, and enhancing the overall well-being of your clients and athletes.

Learn more about nutrition and nutrition for Athletes in the Fitness Nutrition Coach program and the Sports Nutrition Specialist program.