Dose–Response Oxidation of Ingested Phytoglycogen during Exercise in Endurance-Trained Men

Abstract

ABSTRACT Background Phytoglycogen (PHY; PhytoSpherix; Mirexus Biotechnologies), a highly branched polysaccharide extracted from sweet corn, has considerable potential for exercise oxidation due to its low viscosity in water, high water retention, and exceptional stability. Objectives Using gas chromatography–isotope ratio mass spectrometry, we investigated dose–response oxidation of ingested PHY during prolonged, moderate-intensity exercise. Methods Thirteen men (≥1 y endurance-training experience, ≥6 d·wk−1, ∼1–1.5 h·d−1; age, 25.7 ± 5.5 y; mass, 79.3 ± 10.0 kg;  V̇O2max, 59.9 ± 5.5 mL·kg−1·min−1; means ± SDs) cycled for 150 min (50% maximal watt output) while ingesting PHY concentrations of 0.0% (0.0 g·min−1), 3.6% (0.5 g·min−1), 7.2% (1.0 g·min−1), 10.8% (1.5 g·min−1), or 14.4% (2 g·min−1) in water (2100 mL) (n = 7–10/dose). Substrate oxidation was determined using stable-isotope methods and indirect calorimetry. Results PHY oxidation plateaued between 60 and 150 min of exercise and increased (P < 0.001) from 0.49 to 0.72 g·min−1 with 0.5- and 1.0-g·min−1 doses without further increases (0.76 and 0.73 g·min−1; P > 0.05) with 1.5 or 2 g·min−1. Peak PHY oxidation (0.84 ± 0.04 g·min−1) occurred in the final 30 min of exercise with 2 g·min−1. Exercise blood glucose was greater (5.1 mmol·L−1) with 1.0-, 1.5-, and 2-g·min−1 doses compared with that of 0.5 (4.7 mmol·L−1) or 0.0 g·min−1 (4.2 mmol·L−1) (P < 0.0001). Gastrointestinal distress was minimal except with 2 g·min−1 (P < 0.001). Conclusions In male endurance athletes, PHY oxidation plateaued at 0.72–0.76 g·min−1 during 150 min of cycling at 50% Wmax (peak oxidation of 0.84 g·min−1 occurred during the final 30 min). This trial was registered at clinicaltrials.gov as NCT02909881.