What 120 grams per hour truly requires

For most of the history of sports nutrition, 60 grams of carbohydrates per hour was considered the ceiling. Multi-path fueling raised that ceiling to 90. In recent years, some studies have explored 120 grams — and the evidence is more nuanced than headlines suggest.

The 120-gram claim

The idea that athletes can absorb and oxidize 120 grams of carbohydrates per hour comes predominantly from research into highly trained cyclists undertaking very long events. A 2023 review by Podlogar and colleagues looked at carbohydrate oxidation rates at very high intakes in trained cyclists who had undertaken a gut training program. They found that some athletes could achieve exogenous oxidation rates approaching 100–120 grams per hour with a glucose-fructose blend — higher than the typically reported 90.

What sets the ceiling

At the 90-gram per hour intake level, the limiting factors are the transport capacities of the two intestinal pathways: approximately 60 grams per hour for glucose and approximately 30–36 grams per hour for fructose. To reach 120 grams, both pathways must be operating at or above their established limits simultaneously.

Evidence suggests that gut training can upregulate both pathways. But three caveats are important.

The studies reaching 120 grams used very high absolute levels of fructose intake — often 50–60 grams per hour. At this level, the risk of fructose malabsorption increases sharply in athletes who haven’t undertaken extensive gut training.

Inter-individual variability is high. Some athletes will reach 120 grams. Others won’t get over 80 even with gut training.

At 120 grams per hour intake in a six-hour race, you’re taking in 720 grams of carbohydrates. Whether that amount of incoming carbohydrate is practically useful — rather than just theoretically absorbable — hasn’t been fully elucidated.

Practical recommendation

For most trained endurance athletes, 90 grams per hour with an optimized glucose-fructose ratio is the evidence-based practical ceiling. The 120-gram figure is best understood as an aspirational ceiling for elite athletes with extensive gut training — not a starting point for the average ultrarunner or Ironman competitor.

Summary

120 grams of carbohydrates per hour is physiologically possible for some highly trained athletes who have undertaken supporting gut training. The practical recommendation remains 60–90 grams per hour with an optimized ratio, and any progression beyond that should follow a structured gut training program — not guesswork on race day.

References

Podlogar T, Wallis GA. (2023). New horizons in carbohydrate research and application for endurance athletes. Sports Medicine. 53(Suppl 1), S5–S23.

Cox GR, Clark SA, Cox AJ, Halson SL, Hargreaves M, Hawley JA, et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Journal of Applied Physiology. 109(1), 126–134.

Jeukendrup AE. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care. 13(4), 452–457.