Carbohydrates are More Economical than Fat
Carbohydrates are essential fuel for your brain and central nervous system. They can also be used for your working muscles and in a variety of low to very high exercise intensities (1).
Energy production from carbohydrates is quicker and requires less oxygen than fat. This is vital at higher exercise intensities, where efficiency is key. That’s why moderate to high-intensity exercise is mainly powered by carbohydrates and not fat (1-3).
The Size of Carbohydrate Stores in Your Body is Limited
In our body, carbohydrates are stored in the form of glycogen. It is essentially a long, branched chain of glucose molecules that is mainly stored in your liver and muscles (2, 4).
The amount of glycogen in your body is enough to fuel moderate to high-intensity exercise for about 70 to 120 minutes (5). This is in stark contrast to your fat stores which, in theory, could keep you going for several days or longer (2).
This means that you can deplete your glycogen stores quite easily, for example, after a single, long session or when you train for multiple days in a row. That’s why eating enough carbohydrates on a daily basis is a priority for many athletes and for those who lead an active lifestyle (1).
Carbohydrates Enhance Performance During Prolonged Exercise
After about one and a half/two hours of exercise you may find yourself “hitting the wall”. This is because your liver and muscles have run out of glycogen and your blood glucose levels fall. As a result, you slow down, you lose focus and coordination, and your perception of effort starts to go up (1, 6, 7).
Luckily, there is strong evidence to suggest that performance during prolonged exercise is enhanced by consuming carbohydrates (e.g., in the form of a sports drink or gel). This performance-enhancing effect is due to the sparing of your muscle and liver glycogen stores, by providing fuel to your working muscles (1, 3, 6, 8).
Remember to pay attention to your daily carbohydrate intake (before, during and after exercise) so that you have enough of this high-performance fuel in your body when you need to perform at your best.
References
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Hargreaves M, Spriet LL. Skeletal muscle energy metabolism during exercise. Nat Metab. 2020;2(9):817-28.
Burke LM, Hawley JA. Swifter, higher, stronger: What's on the menu? Science. 2018;362(6416):781-7.
Hearris MA, Hammond KM, Fell JM, Morton JP. Regulation of Muscle Glycogen Metabolism during Exercise: Implications for Endurance Performance and Training Adaptations. Nutrients. 2018;10(3).
Fritzen AM, Lundsgaard AM, Kiens B. Dietary Fuels in Athletic Performance. Annu Rev Nutr. 2019;39:45-73.
Cermak NM, van Loon LJ. The use of carbohydrates during exercise as an ergogenic aid. Sports Med. 2013;43(11):1139-55.
Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients. 2019;11(6).
Kerksick CM, Wilborn CD, Roberts MD, Smith-Ryan A, Kleiner SM, Jäger R, et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr. 2018;15(1):38.