All Articles
All Articles Sport Nutrition Fueling Guides In the News Athletes & Partners Diversity Uncategorized Videos

Why Carbohydrate is King for Endurance Performance


Carbohydrate comes in a variety of forms. Sugars, including glucose, sucrose and fructose are all carbohydrates that you may have heard of. While they contain similar calories, they are all metabolized differently, thus affecting our performance output. Maltodextrin is broken down into glucose, which is the base of SiS GO Energy products. SiS GO Isotonic Energy gels, have been shown to get working in 15 minutes (1).


The digestion of carbohydrates for fuel begins when it first enters your mouth until it is absorbed into the bloodstream from the small intestines. The first organ to receive the broken down carbohydrates (glucose, fructose and galactose) is the liver. Here, glucose is either stored (as glycogen) or leaves the liver to be delivered by bloodstream to the muscles so that it may be used for energy . However, the type of carbohydrate that is ingested can determine the speed at which your muscles can use it for energy.


  • Must be converted into glucose in the liver before they can be metabolized (2)
  • Is oxidized at a much lower rate during exercise (2)
  • May cause gastrointestinal issues (stomach cramps/ sickness)
  • Sucrose

    • Also known as table sugar
    • A chemical combination of glucose and fructose
    • Has been shown to digest quickly (3)
    • Maltodextrin

      • Made up of chains of glucose molecules and has a high glycemic index (GI), meaning that energy is available quickly
      • Digested quickly during exercise (2)
      • Reduce the risk of developing gastrointestinal complaints during prolonged exercise (2)
      • At SIS, we use a type of maltodextrin with a particular size of molecule, known as its’ molecular weight. This allows us to balance the amount of energy delivered versus how quickly it empties from the stomach. This means that you will feel the performance benefits of taking on a SiS GO Isotonic Energy gel far more quickly than when a non-isotonic gel is consumed. The risk of upsetting your stomach is also much less. Energy gels with an osmolality close to the gastric content (i.e. isotonic) may promote high carbohydrate delivery to the small intestine compared to thick, concentrated hypertonic gels (4).


        It is common knowledge that some athletes and individuals claim to be “fat adapted” where they can completely use fat as a fuel source during endurance exercise. However, carbohydrate is the fuel for high intensity and prolonged endurance exercise. Although fat may provide more energy, it is used slowly. Carbohydrate yields more energy per litet of oxygen consumed and is a more efficient fuel, providing energy quickly to be used by the working muscles. Although an athlete can enhance the way they use fat a fuel source, potentially sparing muscle glycogen stores (5), race-winning performance is fueled by carbohydrates. As shown in the intensity vs. substrate use graph below, the body is always using a mixture of fuels for energy but this depends on the intensity of the exercise.



        Related Articles:

        • Which Gel, When?
        • The Only Isotonic Energy Gel
        • The role of protein for endurance athletes


          1. Patterson, S. D., & Gray, S. C. (2007). Carbohydrate-gel supplementation and endurance performance during intermittent high-intensity shuttle running. International Journal of Sport Nutrition and Exercise Metabolism, 17(5), 445-455.
          2. Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20(7), 669-677.
          3. Gonzalez, J. T., Fuchs, C. J., Smith, F. E., Thelwall, P. E., Taylor, R., Stevenson, E. J., & van Loon, L. J. (2015). Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists. American Journal of Physiology-Endocrinology and Metabolism, 309(12), 1032-1039.
          4. Zhang, X., O’Kennedy, N., & Morton, J. P. (2015). Extreme variation of nutritional composition and osmolality of commercially available carbohydrate energy gels. International Journal of Sport Nutrition and Exercise Metabolism, 25(5), 504-509.
          5. Impey, S. G., Hammond, K. M., Shepherd, S. O., Sharples, A. P., Stewart, C., Limb, M., & Close, G. L. (2016). Fuel for the work required: a practical approach to amalgamating train‐low paradigms for endurance athletes. Physiological Reports, 4(10), e12803.
          Written By

          Ted Munson (Performance Nutritionist)

          Ted is a Performance Nutritionist here at Science in Sport.