The New Rules of Carb Loading with Sport Scientist Jonah Rosner

Glucose & Fructose

Understanding the balance of glucose and fructose intake during races is crucial for optimal performance. Jonah Rosner explains that while the glucose transport system in the stomach maxes out at 60 grams per hour, fructose can be absorbed through a different pathway, allowing for additional carbohydrate intake. This dual transport system not only enhances energy availability but also reduces gastrointestinal stress by distributing the carbohydrate load across different transporters 1.

By using different transport systems in your stomach via glucose and fructose, we actually see that it can help with stomach or GI stress by spreading out the carbs to those different transporters.

--- Jonah Rosner

Rosner emphasizes the importance of incorporating fructose into pre-race meals to replenish liver glycogen, which is crucial for maintaining energy levels during the race 2.

   

Fueling Strategies

Jonah Rosner and Jason Fitzgerald share their personal strategies for in-race fueling, highlighting the importance of carbohydrate intake. Rosner aims for 90 grams of carbohydrates per hour, using a 2:1 fructose to glucose ratio, and starts consuming gels from the beginning of the race to spare liver glycogen 3. This approach ensures a steady supply of energy and helps maintain performance levels throughout the race.

I'll be having a gel from the start, because I think we see, based on the latest literature, that's going to help give your body extra source of carbs from the start of the race, which is important.

--- Jonah Rosner

Fitzgerald notes that slower marathoners might need more carbohydrates due to longer race durations, as they burn through more muscle glycogen over time 4.