What are carbohydrates and how do they benefit performance?
Carbohydrates are an essential macronutrient that serves as the primary source of energy during exercise, particularly for high-intensity and endurance activities. These nutrients play a vital role in replenishing glycogen stores in muscles and the liver, allowing athletes to sustain performance and delay fatigue. As your workout progresses your body uses glycogen, the stored form of glucose, which is readily mobilized during exercise to meet the increased energy demands, emphasizing the importance of adequate carbohydrate intake. Research has established that consuming carbohydrates before and during prolonged exercise can significantly enhance performance and prolong endurance, highlighting their critical role in sports nutrition [1].
Most common types of intra-workout carbohydrates
Maltodextrin and fructose are both carbohydrates and are amongst most commonly used fast-acting fuel sources during prolonged exercise but differ significantly in their composition and effects on the body. Maltodextrin is a polysaccharide derived from starch and consists of several glucose monomers joined together [2]. Maltodextrin is rapidly digested, providing a quick source of energy that is often used in sports drinks and supplements for immediate fuel during exercise. In contrast, fructose is a simple sugar found naturally in fruits and honey; it is metabolized more slowly and primarily processed in the liver, which can lead to a more sustained energy release but may also contribute to fat storage if consumed in excess. Additionally, maltodextrin has a higher glycemic index, causing faster blood sugar spikes, while fructose has a lower glycemic index, resulting in a more gradual impact on blood sugar levels. These differences make each carbohydrate preferable for different purposes in nutrition and exercise.
The rate of carbohydrate intake
The body can efficiently process up to 90 grams per hour, with some recent studies showing even slightly higher absorption rates of carbohydrates during extended physical activity using various metabolic pathways. Glucose is absorbed through the intestines and transported into the bloodstream via sodium-glucose transporters (SGLT1), where it can be utilized for immediate energy through glycolysis. In contrast, fructose, another simple sugar, is metabolized predominantly in the liver. Through its metabolites, fructose can enter the glycolytic pathway at different points or predominantly convert into glycogen, which is then broken down further into glucose providing an additional, slower-releasing, energy source. This alternate pathway allows athletes to tap into their carbohydrate stores more effectively [3,4].
Combining glucose and fructose during exercise has been shown to improve total carbohydrate oxidation and enhance performance beyond that achievable with glucose alone. Studies indicate that a mixture of glucose and fructose can lead to improved endurance performance due to increased carbohydrate delivery and utilization efficiency. This occurs because the different transport mechanisms for glucose and fructose allow both sugars to be absorbed simultaneously, promoting greater overall carbohydrate availability during exercise [4].
Why the need for carbohydrates during your workout
During about an hour of strenuous exercise, our glycogen stores—primarily found in the muscles and liver—begin to deplete as the body relies on these carbohydrate reserves for energy. As exercise intensity increases, particularly in activities like running or weightlifting, the demand for quick energy rises, leading to the rapid breakdown of glycogen into glucose to fuel muscle contractions. Once glycogen stores are significantly reduced, typically after around 60 minutes of intense activity, performance can decline, resulting in fatigue, decreased strength, and an increased risk of hitting a “wall,” highlighting the importance of proper nutrition and fueling strategies for endurance and athletic performance [5].
In summary, carbohydrates are vital for fuelling physical activity, especially during endurance sports. Understanding their metabolic pathways and developing effective carbohydrate intake strategies can significantly enhance athletic performance and recovery. By optimising carbohydrate consumption before and during exercise, athletes can improve their energy levels and prolong their endurance, reinforcing the importance of these nutrients in sports and exercise regimens.
References:
- Hawley JA, Leckey JJ. Carbohydrate Dependence During Prolonged, Intense Endurance Exercise. Sports Med. 2015;45 Suppl 1(Suppl 1):S5-S12. doi:10.1007/s40279-015-0400-1
- R.S. Chavan, C.D. Khedkar, S. Bhatt,Fat Replacer,Editor(s): Benjamin Caballero, Paul M. Finglas, Fidel Toldrá,Encyclopedia of Food and Health,Academic Press,2016,Pages 589-595,ISBN 9780123849533
- N.L. Keim, P.J. Havel, FRUCTOSE, Editor(s): Benjamin Caballero, Encyclopedia of Human Nutrition (Second Edition), Elsevier, 2005, Pages 351-356, ISBN 9780122266942
- Fuchs CJ, Gonzalez JT, van Loon LJC. Fructose co-ingestion to increase carbohydrate availability in athletes. J Physiol. 2019;597(14):3549-3560. doi:10.1113/JP277116
