Hey guys! We're back with a topic that I, Gabi, love and I'm sure most people do too: Carbohydrates and exercise!

The importance of carbohydrate as a fuel source for exercise and performance is well established and equally well developed are carbohydrate intake guidelines for those seeking to optimize their performance.

As the subject is quite extensive, I will divide it into some parts and in this post I will talk about pre-exercise carbohydrate recommendations.

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It is known that carbohydrate intake in the days and hours before exercise can influence carbohydrate storage and availability in the body and, consequently, affect the ability to perform resistance exercise. In fact, the “carbo-load” concept is rooted in sports nutritional practice. This is based on research indicating that it is possible to overcompensate muscle glycogen stores by consuming a high-carbohydrate diet before exercise, and higher muscle glycogen stores can extend prolonged endurance capacity. If this overcompensation is desired, athletes are advised to consume carbohydrates in an amount of 10 to 12 g/kg per day for 36 to 48 hours before competition.

Such practices may be conducive to optimizing carbohydrate availability for prolonged or intermittent high-intensity events lasting > 90min.

However, when event durations are <90min, such aggressive dietary carbohydrate intakes may not be necessary.

What do you mean, Gabi?

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For example, a study conducted by Sherman and colleagues (1981) found that although increased dietary carbohydrate intake resulted in elevated pre-exercise muscle glycogen stores, this did not translate into improved half-marathon running performance. Therefore, a more appropriate approach would be to scale dietary carbohydrate intake to ensure that there is sufficient muscle glycogen available according to the demands of the subsequent competition, which, from a practical point of view, could mean a daily carbohydrate intake ranging from 7 at 12 g/kg.

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It is also worth mentioning that water is stored in the glycogen synthesis process and, therefore, excessive carbohydrate intake in relation to the demands or needs of the sport can result in unnecessary gain in body mass before competition, compromising performance.

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General guidelines for pre-exercise nutrition are to consume carbohydrates in amounts ranging from 1 to 4 g/kg during the period 1 to 4 hours before exercise. Interestingly, a recent study found that adding fructose to a high-carb breakfast improves endurance capacity in trained cyclists compared to a high-carb breakfast based on glucose alone (Podlogar et al., 2022). And Z2 gels contain both!

It was also seen that pre-exercise consumption of a glucose-fructose mixture increased liver glycogen content due to preferential metabolism of fructose in the liver, and this sustained extended endurance. While more studies are needed, what this means is that nutritional strategies that target glycogen storage in the liver and muscles will likely represent the ideal approach to carbohydrate intake before competition or intense training sessions.

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In summary, endurance competitions or intense training should be preceded by a daily dietary carbohydrate intake ranging from 7 to 12 g/kg depending on energy demands and consume carbohydrate amounts of 1 to 4 g/kg 1 to 4 h before of exercise is recommended for exercises lasting > 60min; Emphasizing that the combination of glucose and fructose carbohydrate sources can benefit endurance performance.

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In the next post I will talk about carbohydrate intake during and after exercise, stay tuned!

References: Bergstrom, J., and E. Hultman (1967). A study of glycogen metabolism in man. J. Clin. Lab. Invest. 19:218-228.

Podlogar, T., and GA Wallis (2022). New horizons in carbohydrate research and application for endurance athletes. Sports Med. In press

Sherman, W. M., D. L. Costill, W. J. Fink, and J. M. Miller (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int J Sports Med 2:114–118.

Thomas, D. T., K. A. Erdman, and L. M. Burke (2016). Nutrition and athletic performance. Med. Sci. Sports Exercise. 48:543–568.