Carbohydrates in Sport
There’s hardly any doubt that carbohydrates are the most important energy source for athletes. Yet it’s still often observed that athletes consume too little energy—and specifically, too few carbohydrates. There are various reasons for this: attempts to lose weight, or trying out popularized diets.
To withstand training loads, recover properly, and be able to perform, there’s no way around an adequate intake of carbohydrates in sport.
Consequences of Carbohydrate Deficiency
An energy deficit can have serious consequences (not only) for athletes. If too few carbohydrates are consumed, this can, for example, lead to an increased injury risk, sleep-onset problems during periods of higher load, disruptions to the hormonal balance, and developmental and growth disorders. A drop in performance is also to be expected.
In a scientific study conducted during a simulated eleven-day training camp, researchers examined how diet composition affected athletes’ ability to tolerate training. It became clear that with a high-carbohydrate diet (8.5 grams per kg of body weight), the athletes’ tolerance (measured in running sessions) deteriorated by around 3%. With a lower-carbohydrate diet (5.4 grams per kilogram of body weight), tolerance decreased by about 7%. The risk of overtraining due to training load can therefore increase with insufficient carbohydrate intake.
Beyond a performance drop, other signs of overreaching were evident. Here, too, there were differences between the two diets. A higher intake of carbohydrates appeared to improve the athletes’ general sense of well-being. [1]
How High Is the Carbohydrate Requirement for Athletes?
In principle, carbohydrate needs rise directly in proportion to training duration and intensity. The longer and harder the effort, the more the glycogen stores of muscle and liver are depleted. To refill them, carbohydrates must be consumed.
For someone who is only occasionally active and does relaxed training now and then, it’s sufficient if about 45–55% of daily calories come from carbohydrates. For athletes, intake should be significantly higher: in endurance sports, 55–65% of daily calories should come from carbohydrates. This corresponds to an intake of 5–8 grams of carbohydrates per kilogram of body weight. [2]
Example calculations:
- 75 kilograms → 5 grams/kilogram body weight = 375 grams per day | 8 grams/kilogram body weight = 600 grams per day
- 55 kilograms → 5 grams/kilogram body weight = 275 grams per day | 8 grams/kilogram body weight = 440 grams per day
In intensive training or competition phases, the recommendation rises to 8–10 grams of carbohydrates per kilogram of body weight. [2]
The Right Carbohydrates for Energy Intake
Not all carbohydrates are processed by the body in the same way. When carbohydrates are consumed during exercise, some are used more quickly than others.
Can be used quickly, for example: glucose, sucrose, maltose, lactose, maltodextrin, and amylopectin.
Slower to become available are, for example: fructose, galactose, isomaltulose, or amylose.
Why isn’t fructose, for example, as quickly available to the muscle as glucose?
These so-called “slow carbs” must first be converted in the liver before the muscle can use them. Fructose is processed in the liver into glucose, which is then available to the muscle. This process makes fructose an energy source that is not immediately available to the body.
Carbohydrates consumed during exercise are oxidized at rates of 1 gram/minute. This oxidation rate of 60 g/h can generally not be exceeded by a single carbohydrate source, whether slow or fast. That means: if you were to consume 100 grams of glucose per hour, only 60 g would actually be used. [3]
For long, intensive training sessions, however, amounts of up to 120 grams of carbohydrates per hour are recommended. So is this recommendation wrong? How is that supposed to work if only 60 grams per hour can be oxidized?
The solution: the right carbohydrates have to be combined.
If you want to learn more about carbohydrate ratios and how they influence absorption, you can read about it HERE (link to carb ratios). It’s important to know that above 60 grams per hour, more than one carbohydrate source is required. Various combinations have proved successful, such as maltodextrin:fructose, glucose:fructose, glucose:sucrose:fructose. [4]
A much simpler approach is to rely on pre-formulated blends in specialized sports nutrition products; then intakes of 100 grams or more per hour are possible, provided this is practiced regularly (“train the gut”).
By the way, whether carbohydrates are available quickly or slowly has nothing to do with whether they are “good” or “bad” carbohydrate sources.
Carbohydrate Intake After Training
Carbohydrates after training are at least as important as before or during training. If you miss the window to refill glycogen stores after exercise, you miss a chance to recover faster and better.
This is especially crucial for athletes who have little time to recover between two sessions and need to make the most of that time.
You achieve optimal recovery by combining carbohydrates and proteins. You can find a detailed explanation of how this looks in another article.
References
1. M. Mountjoy et al., “IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update,” Br. J. Sports Med., vol. 52, no. 11, pp. 687–697, 2018, doi: 10.1136/bjsports-2018-099193.
2. L. B. Baker, I. Rollo, K. W. Stein, and A. E. Jeukendrup, Acute effects of carbohydrate supplementation on intermittent sports performance, vol. 7, no. 7. 2015.
3. A. Jeukendrup, “A step towards personalized sports nutrition: Carbohydrate intake during exercise,” Sport. Med., vol. 44, no. SUPPL.1, 2014, doi: 10.1007/s40279-014-0148-z.
4. R. L. P. G. Jentjens, C. Shaw, T. Birtles, R. H. Waring, L. K. Harding, and A. E. Jeukendrup, “Oxidation of combined ingestion of glucose and sucrose during exercise,” Metabolism., vol. 54, no. 5, pp. 610–618, 2005, doi: 10.1016/j.metabol.2004.12.004.