13C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion
Participants
n=9 trained male cyclists.
Protocol
Randomized repeated-measures design. Each trial was preceded by 24 h of high CHO intake (8 g/kg) and a pre-exercise meal (2 g/kg). 180 min cycling at 95% lactate threshold, then an exercise capacity test at 150% lactate threshold, consuming 120 g/h CHO (1:0.8 maltodextrin or glucose : fructose) in four randomized formats:
1
DRINK — fluid
2
GEL — semisolid gel
3
CHEW — solid jelly chew
4
MIX — coingestion of the forms
Key Results
| Format | Peak exo-CHO oxidation (g/min) | Oxidation efficiency | Exercise capacity at 150% LT (s) |
|---|---|---|---|
| DRINK | 1.56 ± 0.16 | 72 ± 8% | 446 ± 350 |
| GEL | 1.58 ± 0.13 | 72 ± 5% | 529 ± 396 |
| CHEW | 1.59 ± 0.08 | 75 ± 5% | 596 ± 416 |
| MIX | 1.66 ± 0.02 | 75 ± 6% | 469 ± 395 |
No significant differences between formats in peak exogenous oxidation, oxidation efficiency or exercise capacity (all P > 0.05)
Minimal GI distress reported in all conditions despite 120 g/h
Peak exogenous oxidation of 1.56-1.66 g/min is roughly 94-100 g/h (arithmetic: g/min × 60) of the 120 g/h ingested
First study to measure exogenous CHO oxidation with stable isotopes under feeding strategies (pre-exercise CHO feeding, mixed forms during exercise) commonly adopted by elite endurance athletes
Practical Application
Delivery form is athlete preference: in 9 trained male cyclists riding 180 min at 95% LT, 120 g/h of 1:0.8 maltodextrin/glucose:fructose gave the same peak exogenous oxidation (1.56-1.66 g/min), the same oxidation efficiency (72-75%) and the same subsequent exercise capacity whether taken as drink, gel, chew or a mix, with minimal GI distress — pick the form the athlete tolerates and will actually eat.
120 g/h in a 1:0.8 ratio is a practically tolerable strategy for high CHO availability and oxidation (authors' conclusion) — in trained males who had eaten a high-CHO day (8 g/kg) and a pre-exercise meal (2 g/kg) beforehand.
Inference, not tested: mixing forms (MIX) is a sensible default for long events because it spreads palatability fatigue; the study did not test palatability or events longer than 3 h, and MIX's numerically highest oxidation was not statistically different from the other forms.
Not from this paper: the base's ratio rule — 1:0.8 maltodextrin (or glucose):fructose rather than 2:1 for intakes ≥90 g/h — is carried by SYNTH-02; this study used 1:0.8 throughout and did not compare ratios.
Limitations
All-male, small sample (n=9)
3 h exercise — ultra-length palatability and tolerance challenges not captured
Every trial followed 24 h of high CHO intake and a pre-exercise meal; tolerance of 120 g/h without that preparation was not tested
Exercise capacity values are highly variable (SDs comparable to means); the "no difference" is a small-sample null
How this entry was checked and changed
Why this level
regraded 2026-09-26 from A: crossover with 13C tracer, n=9
Content correction 2026-09-27
"gut-trained athletes" -> deleted; the abstract says trained males after 24 h high-CHO intake (8 g/kg) and a pre-exercise meal (2 g/kg), added to Protocol.
"1:0.8 preferred over legacy 2:1 for intakes ≥90 g/h" -> relabelled "Not from this paper" (SYNTH-02); the study used 1:0.8 only.
"MIX reduces palatability fatigue over 5-6 h events" -> relabelled inference; palatability and >3 h not tested. "~95-100 g/h" -> stated as arithmetic from 1.56-1.66 g/min.
Added the exercise-capacity result (150% LT test, no difference between forms, all P > 0.05).
Resync 2026-09-28: Duplicate PMID line -> removed.