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Carbohydrates: the Optimal Fuel for Athletic Performance

Updated: Aug 16, 2023

If carbohydrates are not the foundation of your diet, you’re leaving a lot on the table. Here’s why.


Our Bodies Run Best on Carbohydrates

Put simply, carbohydrates, or 'carbs', are the preferred fuel for moderate- to high-intensity exercise, and the central nervous system (including the brain). Every cell in our body uses glucose—which is what all carbohydrates are eventually broken down into—to create energy. This energy, which is technically called ATP (adenosine triphosphate), is our energy currency, powering all daily activities from those on the lower end of the scale (e.g., jogging), to those on the higher end (e.g., sprinting).


While other macronutrients like fat and protein can also create ATP, neither can match the efficiency of carbohydrates. At lower intensities of activity, this is no big deal—fat, and indeed protein (though very rarely), can be used to meet our energy needs. But when it comes to moderate- to high-intensity exercise, i.e., breaking on the counter-attack, or jockeying a speedy winger, carbohydrates are the energy powerhouse.


How Carbohydrates Fuel Optimal Performance

Briefly, there are three main energy systems in the human body:

  • System one (phosphagen system) can provide energy for the quickest of activities (think of Usain Bolt running the 100m; less than 10 seconds)

  • System two (glycolytic system) can provide a lot of energy quickly without the use of oxygen, but the capacity is limited (approximately 2 minutes)

  • System three (oxidative system) can provide a steady, continuous flow of energy (ATP) using oxygen, but at a lesser rate than system two


Carbohydrates (glucose) can be used to create energy in systems two and three, whereas fat can only be used for system three. This partly explains why carbohydrates are so necessary for performance: in order to perform at the highest intensities, you need to be able to tap into system two. While system three is important, it alone cannot fuel the higher intensity activities that are part and parcel of football. Even for system three, carbohydrates are more efficient energy providers than fat, meaning they can give us more ATP for the same amount of oxygen (1), making carbohydrates the go-to macronutrient for athletes.


High-Carbohydrate Diets Perform Best

In a 2013 study, professional footballers performed at a significantly higher level on match day when eating a *high-carbohydrate diet compared to a low-carbohydrate diet in the lead-up (2). Check out the graphs below: the high-carbohydrate diet ensured players covered more total distance (Figure 1), and more distance at every speed (Figure 2), compared to the low-carbohydrate diet. This made the difference: when players ate a high-carbohydrate diet, they won the match; when they ate a low-carbohydrate diet, they lost.


*High-carbohydrate was defined as 8 grams of carbs per kg of body weight; low-carbohydrate was defined as 3 grams of carbs per kg of body weight


Figure showing differences between high- and low-carbohydrate diets for exercise performance.

Figure 1. The black bars indicate the amount of distance covered when the players ate the high-carbohydrate diet, whereas the white bars show the distance covered when they ate the low-carbohydrate diet. Every player ran more total distance (average +1.3 km) when fed a high-carbohydrate diet in the 3.5 days leading up to the match (2).


Figure showing differences between high- and low-carbohydrate diets for exercise performance.

Figure 2. The black bars indicate the amount of distance covered when the players ate the high-carbohydrate diet, whereas the white bars show the distance covered when they ate the low-carbohydrate diet. Every player ran more total distance at every speed when fed a high-carbohydrate diet in the 3.5 days leading up to the match (2).


This is because the carbohydrates we eat are stored in our muscles and liver, to use when needed most. These stores are called glycogen, and are only topped up by ensuring that carbohydrates are central components of the diet.


This study’s findings are consistent with what we know about how carbohydrates work on a cellular level, and are consistent with other studies showing athletes performing better on a high- vs. low-carbohydrate diet (1).


Summary

Main takeaways:

  • Carbohydrates are the optimal fuel for performance

  • Fat and protein can be used to create energy, but are less efficient than carbohydrates

  • Footballers who eat a high-carbohydrate diet perform better than when they eat a low-carbohydrate diet

  • This finding is consistent across the literature, and explains why established nutrition bodies like the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine all agree that carbohydrates are the most energy-efficient macronutrient (1)


Make sure to check out next week’s post, which is part two of the 'Carbohydrates and Performance' series, where we will discuss what foods are rich in carbohydrates, recommended daily intakes for athletes, and how to optimally fuel both before and after your training session or match.


Consider sharing on social media if you enjoyed this article.


Until next week!


Patrick Elliott, BSc, MPH

Health and Nutrition Science Communication Officer at Training121


Health Disclaimer: This article is for informational and educational purposes only, and is not a substitute for professional advice. For health advice, speak to a physician or other qualified health-care professional, and for nutrition advice, speak to a qualified nutrition professional (e.g., registered dietitian). The use of information on this site is solely at your own risk.


References

(1) Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501–28. Available at: https://journals.lww.com/acsm-msse/Fulltext/2016/03000/Nutrition_and_Athletic_Performance.25.aspx


(2) Souglis AG, Chryssanthopoulos CI, Travlos AK, Zorzou AE, Gissis IT, Papadopoulos CN, Sotiropoulos AA. The effect of high vs. low carbohydrate diets on distances covered in soccer. J Strength Cond Res. 2013;27(8):2235–47. Available at: https://journals.lww.com/nsca-jscr/Fulltext/2013/08000/The_Effect_of_High_vs__Low_Carbohydrate_Diets_on.25.aspx


Technical Terms

ATP: The basic unit of energy used by the human body to power all bodily processes. It is the energy currency of the human body.


Glucose: All carbohydrates are broken down into this simple sugar molecule. It is the only sugar molecule that can be used to create energy (ATP) in the human body.


Glycogen: The stored version of glucose. When we eat carbohydrates, most is stored as glycogen in our muscles and liver.


Macronutrients: These are the energy-providing nutrients in the human diet. The most often consumed include protein, carbohydrates, and fat. Alcohol is also technically a macronutrient, as is water. Water does not provide energy (kcal), though, while all other macronutrients do.


Phosphagen system: The simplest of the three energy systems of the human body. This system can only provide energy for quick activities less than 10 seconds in length. It is an anaerobic process, meaning it does not use oxygen. In this system, energy (ATP) is formed from a molecule called phosphocreatine, which is present in our muscle cells.


Glycolytic system: Like the phosphagen system, the glycolytic system is an anaerobic energy system (doesn't use oxygen). This system can provide energy (ATP) for activities lasting approximately 1–2 minutes in length. It can provide a higher rate of energy than the oxidative system, but is limited in its capacity. The world "glycolytic" or "glycolysis" (which it is also known as) refers to the breakdown of glucose, or "glucose splitting" that occurs in the energy-creation process.


Oxidative system: The most complex of all three energy systems. This system is aerobic, meaning it uses oxygen to create energy (ATP). This system can create a lot of energy, powering most daily activities, as well as lower intensity exercise. Fat and carbohydrate (glucose) are both used to create energy in the oxidative system.

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