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Podlogar, T., Cooper-Smith, N., Gonzalez, J.T. et al. Personalised carbohydrate feeding during exercise based on exogenous glucose oxidation: a proof-of-concept study. Perform. Nutr.1, 2 (2025).
Does every athlete need 90g of carbohydrates per hour? Recent research suggests not.
It’s well established that consuming carbs during exercise is beneficial. Consuming carbs during exercise helps maintain blood sugar, provides energy, and spares liver and muscle glycogen. So, is more fuel always better? It seems the rate at which athletes consume carbs should be very individual.
A recent research study by Tim Podlogar et al. looked to determine the rate of exogenous glucose oxidation (GLUexo) using a high glucose drink (90 g/h) during an exercise trial. Researchers determined the glucose oxidation rate from this initial trial, and then performed a second trial using a personalized glucose dose (PC). The goal in the second trial was to maintain a comparable glucose oxidation rate with lower glucose intake.
Methods
The study examined eleven participants (6 females, 5 males), who regularly engaged in endurance activity. Each participant performed baseline testing, followed by two exercise trials. The trials were a two-and-a-half-hour or steady-state effort on a cycle ergometer at a level equating to 95% of their first lactate threshold (LT1)).
During exercise, participants ingested one of two glucose beverages, enriched with an isotopomer glucose, which allows for the measurement of glucose oxidation. In the first exercise test, participants ingested 90g of glucose drink per hour. Their peak glucose oxidation rates were measured, and these results were used to calculate a personalized glucose dose for each participant. The personalized glucose dose was administered in the second exercise trial.
Dietary intake was kept the same in the twenty-four hours before each trial. Indirect calorimetry measures and blood samples were taken during the exercise trials. Respiratory gas exchanges (V̇O2 and V̇CO2) were measured, and blood samples were obtained every 30 min during exercise. Additionally, heart rate was recorded, perceived exertion was evaluated, and so were ratings of gastrointestinal comfort (GC) and cramping during each of the 30 minute time intervals.
Results
Total carbohydrate oxidation rates did not change significantly over time (p=0.965) or between the two exercise trials. Similarly, fat oxidation rates didn’t change significantly over time (p=0.780) or between exercise trials (p=0.592). As the exercise trials went on, consumed glucose oxidation rates increased over time (p<=.001), but there was no statistically significant difference in this rate increase between the high glucose trial and personalized glucose trial (p=0.473).
Peak glucose oxidation was not statistically significant between the two trials. In the 90 g/h trial, peak glucose oxidation was 0.90±0.15 g/min. In the personalized glucose trial, peak oxidation was 0.91±0.19 g/min.
No significant differences were observed in plasma glucose concentrations between conditions (p=0.996), nor were there differences in plasma lactate concentrations between trials. Heart rate increased significantly over time in both trials (p<0.001).
Heart rate was higher in the 90g/hour trial compared to the personalized glucose trial (p<0.001). Also, ratings of perceived exertion were higher in the 90g/hour trial compared to the personalized glucose trial (p=0.005). Nausea did not differ significantly between the high glucose and personalized glucose trials. Stomach fullness was higher in the 90g/hr glucose trial than in the personalized glucose trial.
The peak glucose oxidation rate varied considerably between participants, with rates ranging from 0.7 to 1.1 g/min (42– 66 g/h). This average oxidation rate was slightly lower than other research where peak exogenous glucose oxidation rates average approximately 1–1.1 g/min (60–66 g/h). The 1.0-1.1 g/min range is the current basis of the recommendations for carb intake during exercise.
The personalized glucose trial produced similar glucose oxidation rates during exercise while providing 28±11% less glucose compared to the 90 g/h trial. This is important, because the personalized glucose trial had lower total carbohydrate intake, resulting in lower ratings of stomach fullness and lower perceived exertion.
Athletes should note that this study was only looking at supplementing with glucose, not a combination of glucose and fructose. A mix of glucose and fructose is recommended when carb intake is greater than 60 g/hr. Future studies should explore the potential to personalize fructose ingestion rates on top of individualized glucose ingestion rates to provide athletes with tailored nutrition recommendations.
What does this mean?
Simply, each athlete should follow an individualized approach when it comes to fueling. Where one athlete may operate well with 90g/carbs per hour, this may be too much for another. Analysis revealed that approximately 68% of the variability in exogenous glucose oxidation rates in this study could be explained by a combination of body height and power output. Meaning that it may be beneficial to consider body size and power output together when determining a fueling plan.
Personalizing carbohydrate intake based on individual needs may help optimize fueling while minimizing the risk of GI distress. Gastrointestinal issues are common during endurance races, and undigested or unabsorbed carbohydrates are thought to contribute to these issues. This is why athletes need to practice their fueling strategies, determining their appropriate intake for their activity. A personalized, well-practiced fueling strategy will be the most effective. Creating a fueling plan appropriate to an athlete’s needs will decrease the likelihood of GI upset, and allow athletes to perform when it matters.
Thank you,
Megan
Reference:
https://performancenutrition.biomedcentral.com/articles/10.1186/s44410-025-00003-9
Podlogar, T., Cooper-Smith, N., Gonzalez, J.T. et al. Personalised carbohydrate feeding during exercise based on exogenous glucose oxidation: a proof-of-concept study. Perform. Nutr.1, 2 (2025). https://doi.org/10.1186/s44410-025-00003-9