Glucose plus fructose kept its oxidation edge even in underfueled athletes

Eleven cyclists completed four arms of a randomized double blind crossover trial. Before each ride they spent 48 hours on either 100% or 50% of their energy needs, then rode 80 minutes at 62% VO2peak while consuming 80 g of carbohydrate as either glucose alone or a 2:1 glucose to fructose blend, followed by a graded test to failure. Substrate use was measured with indirect calorimetry plus oral 13C isotope tracers.

The blend oxidized more of the carbohydrate that was actually consumed than glucose alone, 0.48 vs 0.39 g/min, p<0.001. That advantage held whether riders were in energy balance or in energy deficit.

The better oxidation did not rescue performance. Time to exhaustion was still shorter after the 50% energy diet, and performance did not differ between the two carbohydrate types.

The numbers

Exogenous carbohydrate oxidation, 2:1 glucose to fructose	0.48 g/min
Exogenous carbohydrate oxidation, glucose alone	0.39 g/min, p<0.001
Carbohydrate dose during exercise	80 g over 80 min at 62% VO2peak
Pre trial diet manipulation	48 h at 100% or 50% of energy needs

What this does not show

That anyone went faster on the blend. The outcome that moved was oxidation of ingested carbohydrate. Performance was unchanged between carbohydrate types.
That better fuel offsets underfueling. Riders who spent 48 hours at half their energy needs still reached exhaustion sooner, whichever carbohydrate they took.
That the numbers apply to women. Nine of the eleven riders were male. The findings should not be generalized to female athletes.
That the edge holds at racing intakes. 80 g over 80 minutes is a moderate rate, well below the 100 to 120 g per hour intakes now discussed in racing.

Caveats worth holding

n=11 and heavily male, so the numbers do not generalize to female athletes.
80 g over 80 minutes is a moderate intake rate, below the 100 to 120 g per hour range used in competitive racing.
The measured outcome is oxidation, not race performance. Performance was unchanged between carbohydrate types.
Time to exhaustion remained shorter after the energy deficit diet regardless of carbohydrate type.
Summarized from the abstract; the digest advises verifying against the full text before citing any claim.