Updated: Apr 28, 2021
Carbohydrate is a nutrient that is used primarily for energy during any type of physical activity. Carbohydrates are stored in small amounts in the form of glycogen in the muscles and liver. Glycogen is made up of small glucose units joined together. The liver can store up to approximately 100 g of glycogen (400 kcals), and muscle cells can store up to 400 g of glycogen (1600 kcals). The role of the glycogen in the liver is to keep the blood sugar levels steady. The body allows only a small amount of glucose in the blood (approximately 4 g) to allow the body to function normally. When the blood sugar level is low, the liver will break glycogen down into its basic form (glucose) and release it into the bloodstream. In contrast, the role of muscle glycogen is to provide energy for physical activity.
When liver and muscle storages deplete, athletes must consume carbohydrates to re-stock. Without the required amount of carbohydrates, our body would not be able to perform at its very best and will lead to reduced training intensity and early fatigue. Athletes need to calculate their carbohydrate requirements and plan their nutrition plans accordingly. The more physically active, and the greater the muscle mass is, the higher the carbohydrate needs are.
Older studies used to advocate guidelines based on the percentage of the total diet. However, more recent studies are suggesting that carbohydrate requirements should be based on the person’s body weight. For example, endurance athletes should consume 6-10 g of carbohydrates per kilogram per day (g/ kg/ day), whilst strength athletes should consume 3.9-8.0 g/ kg/ day to ensure the required glycogen stores.
Knowing when to take carbohydrates is equally important. Studies have shown that consuming carbohydrates immediately before and during exercise will help the body refuel depleted glycogen stores, enhancing performance. Consuming carbohydrates immediately after exercise and at set intervals leading to the next workout is important to ensure your body refuels adequate carbohydrate stores for the next workout.
Finally, not all carbohydrates are created equally. The glycaemic index (GI) ranks foods based on the speed food is digested and can raise blood glucose levels. The higher the GI ranking, the higher the speed the food is digested. For example, whole-wheat bread has a GI of 74, whilst a raw apple has a GI of 36. Food with a higher GI index should be consumed immediately after a workout, when glycogen stores need to be replenished. However, when workouts are spaced more than 24 hours apart, the timing of carbohydrates becomes less critical, thus the priority should be choosing more nutrient-dense food.
Remember that the longer and more intense the workout is, the greater the carbohydrate needs will be. The body can store only limited amounts of glycogen stores. When people follow a low-carbohydrate diet, they usually lose quite a lot of weight very quickly which many mistakenly relate to fat loss. However, this weight loss is usually due to reduced glycogen stores and water loss (glycogen stores hold three times their weight in water).
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Thanks for reading, and as always stay fit!
Burke, L. M., Hawley, J. A., Wong, S. H., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of sports sciences, 29(sup1), S17-S27.
Harvard Health Publishing (January 6, 2020) Measuring carbohydrate effects can help glucose management. https://www.health.harvard.edu/diseases-and-conditions/glycemic-index-and-glycemic-load-for-100-foods
Kerksick, C. M., & Kulovitz, M. (2013). Requirements of energy, carbohydrates, proteins and fats for athletes. In Nutrition and enhanced sports performance (pp. 355-366). Academic Press
Oh, R., Gilani, B., & Uppaluri, K. R. (2020). Low carbohydrate diet. StatPearls [Internet].
Wasserman, D. H. (2009). Four grams of glucose. American Journal of Physiology-Endocrinology and Metabolism, 296(1), E11-E21.