Carbohydrate Intake in Ultra-Endurance: Which Dosage: 60, 90, 120g...?
Train Low, Race High Approach
Currently, sports nutrition companies associate ultra-endurance athletes' performances with the amount of carbohydrates consumed during the event. A few years ago, the goal was to consume 90 g/h, but more recently, higher doses of over 120 g/h have been promoted.
This messaging may lead athletes to believe that performance in ultra-endurance depends more on carbohydrate consumption than on the quality of training conducted before the competition. But is it really necessary to consume such a high dose of carbohydrates during an ultra-endurance event (>4 hours of effort) to perform well?
Personally, I was an advocate of HighCarb between 2012 and 2023, using up to 120 g/h with the athletes in my group. However, over time, I noticed that most athletes showed intolerance to these high doses: nausea, vomiting, and diarrhea were common by the end of the event, despite significant intestinal preparation beforehand to improve carbohydrate absorption.
I also noted that an athlete could tolerate HighCarb for one or two years before gradually developing an intolerance, even with a base of 60 g/h of carbohydrates.
This difficulty in absorbing carbohydrates during competition, while being well tolerated during training, may be related to exercise intensity. Indeed, as intensity increases, gastric emptying decreases. The stress of competition may also play a significant role in gastric emptying.
FRUCTOSE: A POTENTIAL CULPRIT?
Carbohydrate absorption in the small intestine is limited by the capacity of specific transporters:
Glucose: Mainly absorbed via the SGLT1 transporter, which can be saturated at around 60 g/h.
Fructose: Absorbed by the GLUT5 transporter, allowing increased total absorption in addition to glucose. Ratios of 2:1 (glucose: fructose) can achieve carbohydrate oxidation rates greater than 90 g/h.
By combining glucose and fructose, it is possible to increase total carbohydrate absorption beyond 60 g/h. Studies have shown that ratios such as 2:1 (glucose: fructose) can reach carbohydrate oxidation rates of up to 90 g/h or more. Therefore, if an athlete wants to follow a HighCarb strategy (90 to 120 g/h of carbohydrates), they will need to consume energy products containing both glucose and fructose.
However, fructose presents potential health problems:
Liver disease: Excessive fructose consumption has been associated with liver diseases, including non-alcoholic fatty liver disease.
Insulin resistance: High fructose intake can contribute to insulin resistance, a precursor to type 2 diabetes.
Inflammation: Excessive fructose ingestion is linked to increased inflammation in the body.
Cancer: Some studies suggest an association between high fructose consumption and an increased risk of certain types of cancer.
It is important to note that these negative effects are mainly observed with high fructose intakes, often from added sugars in processed foods. Fructose naturally present in fruits and vegetables, consumed as part of a balanced diet, is generally not associated with these risks.
Consuming fructose can lead to intolerance to this sugar and may cause intestinal inflammation during exercise, which can lead to gastrointestinal issues. Thus, to use a HighCarb strategy, athletes expose themselves to additional gastrointestinal problems during the event and long-term health concerns.
CARBOHYDRATE OXIDATION DURING EXERCISE
Another point worth discussing about the massive use of carbohydrates during exercise is the rate of carbohydrate oxidation during the effort.
A recent study provides interesting insights:
Carbohydrates Consumed per Hour and Body Size: A recently published article challenges the idea that all athletes have similar absorption capacities, regardless of their size. The results show that:
Taller athletes (190 ± 10 cm) oxidize, on average, 13 g/h more than shorter athletes (178 ± 9 cm). This suggests that a taller athlete could increase their intake to optimize performance.
Carbohydrate Oxidation Rate: The study reveals that despite consuming 90 g/h of carbohydrates:
Shorter athletes oxidize 33 ± 8 g/h.
Taller athletes oxidize 45 ± 13 g/h.
A legitimate question arises: what happens to the 45 to 57 g/h of carbohydrates that are not oxidized?
This raises questions about their potential role:
Storage as glycogen (muscle or liver)
Conversion to lactate
Or simply as an unused surplus, with possible implications for digestive comfort
These observations highlight the importance of a personalized and non-standardized approach to race nutrition, and especially, why consume 90 g/h of carbohydrates if a significant portion is not used?
REVISION OF THE HIGHCARB STRATEGY
After more than ten years of using HighCarb, I began to move away from it. The trigger was a course reconnaissance for EmbrunMan 2023 at specific intensity. During this day, which included 2 km of swimming at EmbrunMan pace, then the 185 km bike loop at 30 km/h average speed (similar average speed during EmbrunMan), and finishing with 14 km of running, including 13 km at Tempo at 4'20''/km (4'15''/km during EmbrunMan), I measured blood lactate levels to refine the nutritional strategy to be used on race day.
Lactate is an indicator of substrate utilization: a low level (<2 mmol/L) reflects predominant fat oxidation, while a high level (>4 mmol/L) indicates a strong dependence on carbohydrates.
During the reconnaissance, lactate levels remained low, except for a peak at 4.7 mmol/L at the top of the Col d'Izoard. During the run, it remained stable at 1.5 mmol/L, indicating preferential fat utilization. These data showed that the energy supply was mainly covered by fats.
Another interesting fact was the performance of Steven GALIBERT, who finished 16th in the EmbrunMan 2023 with the 2nd fastest marathon time of 2:51:50, averaging 4'04''/km (2'39'' behind the best time by Arthur HORSEAU, who dominated the race) with an intake of 60 g/h, compared to approximately 120 g/h during his 2:36:18 marathon at the Girona Full Distance Triathlon 2023. These two performances were relatively similar despite a lower carbohydrate intake, considering different conditions:
Marathon course profile: EmbrunMan (D+450m) vs. Girona (D+100m)
Temperature: ~35°C during the EmbrunMan marathon vs. ~23°C during the Girona Full
These observations led me to question the HighCarb nutritional strategy. Is it really necessary to consume 90 to 120 g/h of carbohydrates to be performant, when nothing shows that this approach is required for ultra-endurance competitions? The recent difficulties of Norwegian triathletes Kristian BLUMENFELT and Gustav IDEN during the Ironman Hawaii, with gastrointestinal issues, also raise questions about the validity of the "more carbohydrates" strategy.
Through three case studies, Louis RICHARD at EmbrunMan 2024, Steven GALIBERT at IM Nice 2024, and Kilian JORNET during his victory at UTMB 2023, I will show you that another path is "potentially" possible.