Is 120g of carbohydrates per hour or greater optimal for endurance athletes?

Endurance athletes can often struggle to maintain their energy during lengthy workouts or races lasting longer than 2 hours. Subsequently, one recommendation gaining increasing popularity over recent years is consuming 120 grams of carbohydrates per hour with the suggestion that it can boost performance. But is this amount truly effective for everyone involved in endurance sports? This article explores the science of carbohydrate intake and looks into whether this guideline suits all endurance athletes.

Understanding Carbohydrate Needs

Carbohydrates are essential for endurance athletes, serving as their main energy source. During extended exercise, the body depends heavily on glycogen stores from carbohydrates. Some research and anecdotal evidence, particularly from elite athletes, supports the idea that an exogeneous intake of 120 grams per hour can be tolerated and aid performance. For example, one study (Viribay et al., 2020) found that runners who consumed this amount completed a mountain marathon significantly faster than those who consumed either 60 or 90 grams per hour. However, it is important to consider the athletes in this study were elite level runners including 2 world champions.

Nonetheless, each athlete's carbohydrate requirements can vary widely based on factors such as body weight, exercise intensity, and duration. So should we all be coping the elite athletes strategies?

Daniela Ryf grabs refreshments while running through an aid station.

There is no denying that consuming carbohydrates during exercise can lead to better performance. Previously it was believed that the body can absorb carbohydrates at a general rate of about 60 grams per hour. However, newer research now suggests that intakes of up to 90 grams per hour, especially from different carbohydrate sources, can increase efficiency and exercise performance due to unique absorption pathways in the gut. For instance, combining glucose and fructose can allow for higher overall carbohydrate utilization.

However, back to the question of whether we should all be aiming for higher intakes of 120 grams per hour or more, this idea has in part been fuelled by the increasing number of elite athletes reportedly adopting such strategies, but there are a few points to consider before deciding whether to try this for yourself.

Limiting factors

One factor we need to consider is oxidation efficiency, that being the actual amount of ingested carbohydrate that is used for oxidation and energy provision. Whilst some studies and elite athletes have shown that 120 grams per hour or greater can be tolerated, this doesn't mean all of it is being used to aid performance. A study by Dr Tim Podlogar and colleagues compared 90 grams vs 120 grams per hour during three hours of cycling. Their key findings were that only 75% of ingested carbohydrates for the 120 gram trials were oxidised. Therefore, what is happening with the remaining 30 grams? This as present is unknown.

Another finding from this study was that the higher carbohydrate intakes also did not spare glycogen stores for potential use later in events, thus does not have the potential to reduced fatigue and ultimately you woudl end up using similar amounts of glycogen, though it may slow down fat use. However, Podlogar and Co did also state that there may be some potential in using a 120 grams per hour strategy once glycogen stores are fully depleted, but also concluded this still requires further research and any benefits would be relatively small anyway.

Another consideration is time. Generally, elite athletes have the benefit of having more time to spend on practicing their nutrition strategies and the higher intakes during training that most amateur and recreational athletes do not. As with any other muscle the gut requires training to tolerate these high intakes which doesn't happen overnight. However, this process is highly individual and can take several months of practice for some athletes. Additionally, there is currently limited evidence that gut training has a significant effect on how much carbohydrate is actually oxidised, though it does improve gut discomfort.

Lastly, consideration needs to be given to the type of exercise being performed. Much of the current research has been conducted using cycling as a mode of exercise, where unlike during running the gut is less agitated. Therefore, for runners a more conservative approach using up to 80-90 grams per hour may be better, whilst for multisport athletes such as triathletes front loading their carbohydrate intake during the bike leg may be a better strategy to avoid potential gut issues on the run due to the mechanics of running.

Kendal Mint Co. KMC_NRG_Gel. Image credit James Vincent.

Final Thoughts

Whilst 120 grams of carbohydrates per hour can be beneficial for some endurance athletes, it is not a universal recommendation. Individual needs vary based on body weight, exercise intensity, and personal preferences. However, based on current research 90 grams of carbohydrates per hour would appear to a more practical and relevant intake for the majority of endurance athletes.

Likewise, carbohydrate source is also important to consider. For single source carbohydrates such as glucose then up to 60 grams per hour is best, whereas for multi-source carbohydrate combinations (glucose-fructose), which are the preferred type for activities lasting longer than 2 hours, 60-90 grams per hour is best.

If you would like more information on carbohydrate ingestion or need support with your race fuelling get in touch and we will be happy to help.

Dr Howard Hurst.