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David E Barney¹, Kimberly N Panik¹, Julia Michalak¹

¹Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, MA, United States; Oak Ridge Institute for Science and Education, Belcamp, MD, United States.

The Journal of Nutrition

|May 14, 2026

Abstract

Background:

When glucose (GLU) is consumed during endurance exercise in an energy deficit state (DEF), exogenous carbohydrate oxidation is lower than in energy balance (BAL). Whether consuming multiple transportable carbohydrates, such as glucose + fructose (GLU+FRU), better maintains exogenous carbohydrate oxidation during DEF is unclear.

Objectives:

This study assessed the effects of consuming GLU + FRU compared with GLU on substrate oxidation and physical performance during BAL and DEF.

Methods:

Eleven participants (sex: n = 2 females, 9 males) completed this double-blind randomized crossover study (clinicaltrials.gov: NCT06394401). Participants completed 4 study arms, each initiated by a bout of cycling followed by 48 h of consuming BAL or DEF diets (100% or 50% energy needs). After each diet, participants consumed 80 g GLU or GLU + FRU (2:1 GLU:FRU; 36.0 g at 0 min and 14.7 g at 20, 40, and 60 min) during 80 min of steady-state cycling (62 ± 4% V̇O₂peak). Participants then completed a graded exercise performance test, cycling under progressive intensity (+30 W every 2 min) until volitional failure. Substrate oxidation (g/min) during steady-state cycling was determined by indirect calorimetry and oral ¹³C isotope tracers. Data were analyzed by linear mixed models and are presented as means ± SDs.

Results:

Independent of carbohydrate treatment, total carbohydrate oxidation was lower (P < 0.001) and fat oxidation was higher (P = 0.003) during DEF than BAL. Exogenous carbohydrate oxidation was higher when consuming GLU + FRU (0.48 ± 0.09) compared with GLU (0.39 ± 0.07, P < 0.001), regardless of energy status. Endogenous carbohydrate oxidation was lower during DEF (1.02 ± 0.40) than BAL (1.14 ± 0.39, P < 0.001) but did not differ between GLU + FRU (1.06 ± 0.38) and GLU (1.11 ± 0.41, P = 0.19). Regardless of treatment, time-to-exhaustion was shorter during DEF (576 ± 138 s) than BAL (599 ± 142, P = 0.043).

Conclusions:

Findings indicate that regardless of energy status, exogenous carbohydrate oxidation is higher when consuming GLU + FRU compared with GLU. However, differences in exogenous carbohydrate oxidation did not prevent the negative effects of DEF on physical performance.

Keywords:

carbohydrate supplementation endurance performance energy deficit multiple transportable carbohydrate substrate oxidation

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