Nutrition, Podcast

Carbohydrate intake in racing – a case for going very high with Aitor Viribay Morales (Astana Pro Team) | EP#269

 January 18, 2021

By  Mikael Eriksson


Aitor Viribay Morales is a performance nutritionist at Astana Proteam (a World Tour cycling team) with a background in science and academia. In this interview we discuss his research findings and practical experience with ingesting really high amounts of carbohydrate (up to 120 g/h) in races, and the effects such high-carb strategies can have.

In this Episode you'll learn about:

  • Aitor's studies in mountain marathon runners on high-carbohydrate (up to 120 g/h) intake during racing and its effects
  • Performance effects, recovery effects, and muscle damage effects of high-carbohydrate intake in races
  • Is there not an absorption rate limit of 90 g/h as we have been told?
  • How to train the gut to absorb 120 g/h of carbohydrate
  • How do the potential benefits of high-carbohydrate intake in racing relate to training?
  • Metabolic flexibility, and the height and width of the fat oxidation curve
  • Practical takeaways

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05:15 -

  • My name is Aitor Viribay Morales and I am a researcher within the field of sports science, physiology and metabolism, particularly focusing on nutritional aspects of these subjects.

    I also work with the Astana Pro Cycling Team as a sports performance consultant.

    In my youth, I was also a professional cyclist myself.

Research study: Pushing the limits of carbohydrate intake in racing

08:05 -

  • It all started as we were observing that athletes who took in plenty of carbohydrates during trail running races seemed to perform better.

    Hence, we wanted to investigate this scientifically and therefore we designed and conducted a study on the topic.
  • We divided a group of runners participating in a trail running race into three sub groups: one group that took in around 60g of carbohydrates per h, one group who took in 90g per h (what is currently consider to be the upper limit of what the body can absorb during exercise) and one final (the experimental) group that took in 120g per h.
  • As outcome parameters we looked at performance between the groups, muscle damage markers (creatinine kinase and lactate dehydrogenase) as well as different kind of recovery measurements (muscle function 24h post race, glycolytic capacity 24h post race).

    We did see a trend towards better performance and significantly less muscle damage and signs of enhanced recovery in the group that had taken in 120g of carbohydrate per h during the race.
  • Even though the results were surprisingly strong, we weren’t too shocked by the outcome since we have witnessed athletes (like cyclists and triathletes) taking in far more than 90g per h with good results previously to the study.

    However, these athletes have all ”trained their gut”, i.e. practicing taking in more than 90g per h during training, quite extensively.

    The study subjects did, however, get a chance to familiarize with taking in over 90g per hour (twice a week during four weeks leading up to the study), but this is actually a rather short period of time and few occasions to train your gut for this kind of ”load”.
  • One needs to point out, however, that a considerable amount of the athletes in the 90 and 120g per h-group were not able to finish the race due to gastro intestinal issues, indicating that it actually is quite taxing for the gut to take in this large amount of carbohydrates during exercise.

    So conclusion wise, one can say that for those who tolerate this amount of carbohydrate intake it appears to be beneficial.

Mechanistic explanations

20:40 -

  • The current recommendation of 90g of carbohydrates per h is based on the knowledge of gastrointestinal glucose and fructose transporters, which are believed to be saturated at around 60g/h (glucose) and 40g/h (fructose).

    Therefore, we have thoroughly discussed potential mechanistic explanations to why plenty of athletes still tend to benefit from taking in higher amounts of carbohydrates than this.

    We have not landed in any concrete theory, but the knowledge about the fructose transporters is generally not as extensive as the one that exists for the glucose transporters, so my guess is that the explanation has something to do with the transport mechanism of fructose.

    Here one must also point out that a high intake of fructose is generally associated with more gastrointestinal distress than a high intake of glucose.

Suppression of adaptive signals when taking in plenty of carbohydrates?

25:10 -

  • As we did find considerably less evidence of muscle damage in the group who took in 120g/h, this may raise the question that a high carbohydrate intake may suppress adaptive signaling, leading to a lower training response.

    However, the plasma levels of creatinine kinase seen in this study were so high that they most certainly were ”non-functioning”, and hence it is less likely that they would generate further physiological adaptions.

Future research

35:35 -

  • In the future I would like to see more research done on how to best train the gut to be able to tolerate a very high intake of carbohydrates.

    I also think that this study may affect the way athlete address food in general, it reinforces the impression of that carbohydrates are very important for being able to perform both in training and racing.

    Additionally, I would also like to see more research done on other supplements that may affect the ability of the gut to absorb carbohydrates.

Practical take home messages from the study

48:25 -

  • I would say that the main take home message from the study is that athletes should really start training the gut to start tolerate and absorb large quantities of carbohydrates during exercise.

    It appears that this ability is very trainable but it can take time and one needs to have a careful approach towards it and take small steps at the time.

Metabolic flexibility

52:40 -

  • Metabolic flexibility basically mean that you are effective at using both fat and carbohydrates as a fuel.

    If an athlete would adapt a very strict low-carb diet, then of course this athlete’s fat metabolism would spike quite high, however, the same athlete’s ability to utilize glucose as a fuel will suffer and hence also the athlete’s ability to do high intensity work.

    By being metabolically flexible, one has a good capacity to utilize fat (however it won’t get equally high as those who adapt a low-carb diet) and a good ability to use carbohydrates as a fuel on the same time, which in most cases is very desirable.
  • To become metabolically flexible, the training is the most important component, one needs to train plenty of volume and rather much high intensity as well in order to give the mitochondria a really good stimulus for them to be effective at oxidizing both fat and glucose.

Rapid fire questions

01:00:40 -

  • What’s your favorite book, blog or resource related to endurance sports? I like several blogs, and in terms of books I am actually more of a ”scientific paper kind of person”, also I think that the best way to learn is to practice yourself!
  • What is a personal habit that has helped you achieve success? Being in contact with nature, exercise outside and spend plenty of time with my best friend, which is my dog.
  • Who is someone you look up to or has inspired you? Inigo San Millan!


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

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