Personalised carbohydrate feeding during exercise based on exogenous glucose oxidation: a proof-of-concept study

Carbohydrate (CHO) feeding during prolonged exercise is well-established for its ergogenic effects primarily by maintaining glycemia and carbohydrate oxidation. Current CHO intake guidelines propose broad intake recommendations based on exercise duration. Recent evidence demonstrating individual differences in exogenous CHO oxidation suggests a need for personalised approaches. This study aimed to determine whether exogenous glucose oxidation (GLUexo) rates achieved with a high glucose dose (90 g/h) could inform a personalised glucose dose (PC) that maintains comparable GLUexo with reduced intake. Eleven endurance-trained participants (6 females, 5 males; V̇O2 peak: 59.2 ± 7.3 mL/kg/min) completed two 150-min cycling exercise bouts at 95% of the intensity corresponding to the first lactate threshold with different glucose intakes: a high glucose dose (90 g/h) and a PC dose. Drinks were enriched with U-13C glucose allowing for estimation of GLUexo rates. Peak GLUexo was first determined with the high glucose dose. The PC dose was calculated assuming the peak GLUexo would represent an oxidation efficiency of 80%. The PC dose provided 28 ± 11% less glucose (mean: 65 ± 10 g/h) compared to 90 g/h, yet peak GLUexo was not any lower with PC (0.91 ± 0.19 g/min) vs. 90 g/h (0.90 ± 0.15 g/min; p = 0.977). Bland–Altman analysis showed good agreement between trials (mean bias: 0.00 g/min; limits of agreement: ± 0.20 g/min). Differences in plasma glucose, lactate concentrations, or endogenous CHO oxidation rates between conditions were not statistically significant or biologically meaningful. Ratings of perceived exertion and stomach fullness were lower with PC compared to 90 g/h (p < 0.05). Personalised glucose feeding strategies based on direct measurement of individual GLUexo rates can optimise glucose provision during exercise by achieving comparable oxidation rates with reduced glucose intake, whilst simultaneously minimising perception of effort and gastrointestinal discomfort.