Through many studies, we now know that the ingestion of carbohydrates during exercise longer than 30 minutes enhances exercise capacity – also called endurance capacity – and improves exercise performance. The proposed mechanisms by which this takes place have been reviewed in a previous blog that I encourage you to take a look at if you want to refresh it.
But you may agree with me that knowing about this ergogenic effect of carbohydrates is completely useless if we don’t know how to put it into practice. How do we achieve it? What are the practical guidelines of carbohydrate ingestion during exercise? What is the recommended amount? And does the type of carbohydrate matter?
In this blog I will try to answer all these questions with the most updated research. I will talk about the current carbohydrate recommendations, developed by Asker Jeukendrup in 2014, which gather the most updated knowledge about carbohydrates as an ergogenic tool and includes information about the amount and type of carbohydrate depending on the duration of exercise.
Let’s begin this journey!
What do carbohydrate recommendations depend on?
First of all, let me talk about the factors that may alter the carbohydrate recommendations exposed here.
In the next section, we’ll give recommendations about the amount of carbohydrate ingested during exercise to achieve optimal performance. However, several factors can make the recommended amounts be different and, therefore, they may have to be adjusted either downwards or upwards. The most important factors we should take into account when planning the nutritional strategy during a training session or competition are:
- Intensity of exercise.
- Duration of exercise.
- Personal tolerance.
- Weather and environmental conditions.
It is important to mention that carbohydrate recommendations during exercise do not depend on body weight. This is because it appears to be no correlation between body weight and exogenous carbohydrate oxidation since the limiting factor is carbohydrate absorption, which is largely independent on body weight. You can review how carbohydrates are absorbed in the intestine here.
Now, why don’t we go over each of these factors very quickly to understand them? Follow me!
Intensity of exercise
In a previous blog, we reviewed how the intensity of exercise influences substrate utilization. Very briefly, the higher the intensity of exercise, the greater the reliance on carbohydrates as an energy fuel and, thus, the oxidation rates of carbohydrates.
In line with this, carbohydrate recommendations detailed here are appropriate for those exercise bouts at moderate-to-high intensity (>60-75% VO2 max) during which optimal performance is crucial for maximizing adaptations. If exercise intensity is lower, the following recommendations may have to be adjusted downwards.
Remember that the aim of carbohydrate ingestion during exercise is to achieve optimal performance.
Duration of exercise
At moderate-to-high exercise intensities, glucose is the main energy fuel. In our body, glucose is stored as glycogen in relatively small amounts. Unlike fat, endogenous glycogen stores can be all used up within 90 min of exercise at 75% VO2 max.
Therefore, the longer we exercise, the more carbohydrates we need supply our body with in order to maintain exercise intensity. Otherwise, we will start bonking – term used to describe the dizziness and weakness sensation caused by glycogen depletion – and consuming fat at the expense of carbohydrate as an energy fuel, which will result in reduced exercise performance.
But this would only explain the benefits of carbohydrate ingestion during exercise bouts longer than 60 minutes. However, many studies have shown that carbohydrate ingestion during exercise also benefits athletes who compete in events shorter than 60 minutes, although it seems that 30 minutes is the minimum length to have positive effects.
As always, the principle of individuality is extremely important, not only for training but also in sport nutrition. Some people may tolerate and absorb higher amounts of carbohydrate than others, and therefore the recommended amounts may have to be adjusted for each individual person.
And here it comes into play the famous strategy developed by Asker Jeukendrup commonly known as “Training the Gut”. Very briefly, training the gut refers to a process of adaptations of the gastrointestinal tract to increase the tolerance threshold to food and beverages as well as the absorptive capacity of nutrients, which results in reduced gastrointestinal distress and optimal use of the nutrients ingested. You can read more about it here.
Then, by training the gut, we can increase our personal tolerance and reach the recommended amounts.
Weather and environmental conditions
The weather and the different environmental conditions influence the way our body uses substrates. Depending on the temperature, humidity, radiation, and even altitude, carbohydrate recommendations can change significantly. For example, the glycolytic pathway is accelerated at high altitudes over the sea level, thus increasing the demand for glucose.
Also, the weather and the environmental conditions may alter the nutritional priorities of the athlete, which can limit carbohydrate intake. For example, hydration is the priority when exercising in hot environments, which reduces the amount of carbohydrates we can take in.
Therefore, carbohydrate recommendations should be adjusted to each situation.
Running is not the same than cycling. Have you ever tried to eat an energy bar on the bike, and then do the same while running? If you have, you probably noticed that the impact when running makes it way more difficult to eat and drink than cycling and, thus, recommendations may have to be adjusted downwards for running athletes in order to avoid gastrointestinal distress – at least at the beginning, until they train their gut and become more comfortable with higher amounts of carbohydrates.
Also, the sport we practice may also dictate the amount of carbohydrate we can take in. Some sports allow continuous supply of food and drinks, while others only have several minutes to do so or even do not allow for any exogenous energy supply.
Every sport should have their own carbohydrate recommendations.
Now we know what the guidelines for carbohydrate intake during exercise depend on. Let’s move on and talk about the actual carbohydrate recommendations!
Amount of carbohydrate
Recommendations for the amount of carbohydrate during exercise described here are dependent on exercise duration and, as we mentioned above, they assume that exercise will be “all-out”. Let me just point out that there is no scientific evidence supporting beneficial effects of carbohydrates during events that are shorter than 30 minutes. Because of that, carbohydrate recommendations begin at exercise bouts that last 30 minutes and extend to ultradistance events:
- From 30 min to 60 min. Ingesting carbohydrates is not necessary, but a mouth rinse with a carbohydrate solution has been shown to improve performance through the central nervous system. Both practices are equally beneficial although during this type of events it is not always practical to ingest carbohydrates and it may result in gastrointestinal problems. Therefore, it is up to the athlete to swallow the carbohydrate solution or simply rinse their mouth with it.
- From 60 min to 90 min. Ingesting 30 grams per hour is sufficient to achieve beneficial effects during this type of events.
- From 90 min to 2.5 hours. Increasing carbohydrate intakes to 60 grams per hour is recommended.
- Longer than 2.5 hours. Intakes of 90 grams per hour or even higher, as long as gastrointestinal problems don’t arise, are recommended.
Interestingly, there seems to be a dose-response relationship between the amount of carbohydrate ingested and the increase in exercise performance, especially when exercise duration exceeds 2 hours. Because of that, intakes over 90 grams per hour are recommended as long as no gastrointestinal problems appear.
In fact, many world-class athletes such as Kipchoge in track and field (marathon world record), and Chris Froome, Egan Bernal, Tadej Pogačar, Primož Roglič and many other professional cyclists already reach intakes above the recommended 90 grams per hour, even reaching 120 grams per hour, and are obtaining extraordinary results.
Is this the secret of their success?
Type of carbohydrate
When ingesting carbohydrates at a rate lower than 60 gram per hour, any rapidly oxidized carbohydrate will be fine – glucose, sucrose, maltodextrins, and some starches. However, if we are consuming carbohydrates at a higher rate, mixtures of glucose and fructose – multiple transportable carbohydrates – are required.
Let’s see why!
In a previous blog we went over the mechanisms of carbohydrate absorption in the intestine, which is the rate limiting step for exogenous carbohydrate oxidation, as mentioned earlier.
In that article we saw that glucose uses the sodium-dependent transporter 1 (SGLT1), which is thought to become saturated at 1 g/min (60 g/h). In other words, the maximal rate of glucose absorption is about 60 g/h.
Then, how can we achieve carbohydrate intakes higher than 60 g/h? Well, we also mentioned that fructose uses a different transporter (GLUT5), which is thought to become saturated at 0.5 g/min (30 g/h). By combining fructose and glucose – and thus using two different transporters – their maximal rates of absorption add up and intakes of 90 grams per hour can be achieved. It has also been shown that glucose-fructose mixtures reduce gastrointestinal problems compared to glucose only in isocaloric amounts.
Guidelines for carbohydrate ingestion during exercise end here since solid, supportive scientific evidence also ends here. But, in practice, higher absorption rates have been achieved despite the underlying mechanisms for that are not completely understood. It is believed that the glucose transporter GLUT2 – it transports glucose from the enterocyte to the systemic circulation – translocates to the basal membrane in response to high carbohydrate intakes and aids in their absorption from the intestinal lumen. This may explain, at least partially, the extraordinary high carbohydrate intakes seen in many top-level athletes.
Science is destinated to be always behind reality, and there are many phenomena for which we don’t have an explanation yet. We should not limit our possibilities to succeed but seek for explanations and underlying mechanisms for what we see it is possible through science.
As in all cases, the success of any strategy is practice, practice, and practice. Here, specially when somebody is reaching carbohydrate intakes over 30 grams per hour, training the nutritional strategies and getting used to them is crucial. This will reduce gastrointestinal problems as a result of adaptations in the gut, which will result in enhanced exercise performance.
These carbohydrate guidelines can be achieved through either energy bars, gels, chews, carbohydrate-containing drinks and food. Carbohydrate-containing drinks, gels, and chews are the most appropriate carbohydrate sources for most situations. However, when the duration of exercise increases (I would say to 90 minutes or more, although this is merely personal) solid foods like energy bars or the popular “rice cake” are necessary.
Also, as exercise duration increases, so does the relevance of the taste of food. By alternating sweet and savory food we manage to reduce the chances that our athlete becomes saturated of eating and increase his or her ability and desire to eat more, which results in higher carbohydrate intakes and, in turn, greater exercise performance.
Finally, don’t forget that carbohydrate intakes should be balanced with a fluid intake plan.
It is clear that carbohydrate ingestion during exercise increases exercise capacity and, thus, exercise performance. But it is fundamental to know how to implement this strategy during training sessions and competitions.
To achieve such effects, guidelines of carbohydrate ingestion during exercise have been established by gathering all the available information. Not only these carbohydrate recommendations advices about the amount of carbohydrate, but they also give directions regarding the type of carbohydrate that it should ingested in each situation.
I hope you found this blog interesting and useful! See you soon!
- Jeukendrup, Asker. 2014. “A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise.” Sports Medicine 44: 25–33.
- Not all carbs are equal – Jeukendrup A. – Mysportscience