Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h -1 versus 90 g h -1 at different ratios.
Level 2 - randomized trial
Controlled crossover experimental trial in humans
PubMed 35951130 · doi:10.1007/s00421-022-05019-w
What was done
Eleven highly trained male cyclists (VO2peak 62.6 ± 7 mL·kg⁻¹·min⁻¹) completed 4 experimental visits involving 3 hours of cycling at 95% of gas exchange threshold following an overnight fast. Participants ingested fructose and maltodextrin labeled with 13C stable isotopes at either 120 g·h⁻¹ (0.8:1 fructose:maltodextrin ratio) or 90 g·h⁻¹ (1:2 ratio) to measure exogenous and endogenous carbohydrate oxidation rates.
What was found
Exogenous carbohydrate oxidation rates during the final hour (120–180 min) were significantly higher with 120 g·h⁻¹ compared to 90 g·h⁻¹ (1.51 ± 0.22 vs. 1.29 ± 0.16 g·min⁻¹, p = 0.026). Endogenous carbohydrate oxidation rates did not differ significantly between conditions (2.15 ± 0.30 vs. 2.20 ± 0.33 g·min⁻¹, p = 0.786).
Why it matters
High-dose carbohydrate feeding (120 g·h⁻¹) with a higher fructose-to-glucose ratio enables greater absorption and oxidation of ingested carbohydrates during prolonged exercise, but does not provide additional glycogen-sparing benefits compared to standard 90 g·h⁻¹ guidelines.
Limits
The study had a very small sample size (n = 11) limited strictly to trained male cyclists. It measured acute physiological gas exchange and isotope kinetics without assessing gastrointestinal comfort or endurance performance outcomes.
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.