From Metabolism to Medals: Contemporary Perspectives and Revisiting Carbohydrate Guidelines for Fueling Endurance Athletes during Exercise.
Level 5 - mechanism / opinion, no new human data
Narrative review and expert opinion synthesizing mechanistic and performance literature without systematic review methodology.
PubMed 41759826 · doi:10.1016/j.tjnut.2026.101442
What was done
This narrative review synthesizes historical and contemporary research on carbohydrate metabolism, exogenous carbohydrate oxidation rates, and sport-specific performance demands during prolonged endurance exercise (>2.5–3 h). The authors evaluate 2016 American College of Sports Medicine guidelines against emerging field practices and outline a personalized fueling model.
What was found
The abstract reports no quantitative trial data or pooled statistics. It states that while 2016 guidelines recommend carbohydrate intake ≤90 g/h, contemporary evidence indicates that trained athletes can increase exogenous and whole-body carbohydrate oxidation at intakes up to 120 g/h. Ingesting higher doses (120–200 g/h) currently lacks scientific substantiation.
Why it matters
This paper proposes revising standard sports nutrition practice by raising the recommended upper limit of intra-exercise carbohydrate fueling from 90 g/h to 120 g/h for trained endurance competitors.
Limits
This is a narrative review incorporating practitioner insights rather than a systematic review or randomized trial. The abstract provides no sample sizes or effect sizes. Doses exceeding 120 g/h remain unsubstantiated, and the authors note a scarcity of research in female athletes and ecologically valid settings.
Cited by
- contradicts Consuming 120 grams of carbohydrates per hour during prolonged strenuous exercise suppresses fat metabolism to approximately 10% of total energy expenditure and shifts over 85% of fuel utilization to glucose, primarily from muscle glycogen.
- supports Studies published in JAMA in 1924 and 1925 by Gordon and Levine showed that low blood glucose caused glycopenia and early onset fatigue in Boston Marathon runners.