Lower oxidation of a high molecular weight glucose polymer vs. glucose during cycling

We previously reported no difference in the oxidation rate of a high molecular weight glucose polymer (GP) vs. maltodextrin (8 kDa) during exercise; however, the ingestion rate (1.8 g·min(-1)) was above the glucose absorption-oxidation maxima (∼1.0 g·min(-1)), possibly masking either faster gastric emptying of the GP and delivery to the circulation observed at rest or physical properties of the GP that might slow intestinal absorption. Therefore, we asked whether GP oxidation could be differentially affected when ingested at a lower rate (0.8 g·min(-1)). Eight cyclists performed three 150-min rides at 50% peak power while ingesting solutions containing 8% GP (500-750 kDa, 21 mosm·kg(-1)), 8% glucose (469 mosm·kg(-1)), or water. The exogenous carbohydrate oxidation rate was determined using stable isotope methodology and indirect calorimetry. Glucose and GP were oxidized on average at 0.54 g·min(-1) (coefficient of variation (CV) 37%) and 0.41 g·min(-1) (CV 60%), respectively, which equated to a moderate (effect size) reduction of 24% (90% confidence limits: ±22%) with GP. The endogenous carbohydrate oxidation rate with glucose (1.04 g·min(-1); CV 68%) was not clearly different from GP (15%; 90% confidence limits: ±24%) and total carbohydrate oxidation rate was not affected. Plasma glucose concentration was 8.3% lower (±7.0%, moderate) and nausea 0.4 units higher (±0.4 units, moderate) with GP vs. glucose. To conclude, the oxidation rate of GP when ingested below the glucose absorption-oxidation maxima is slower than glucose. Further work could determine the physical properties of the carbohydrate and (or) physiological mechanism determining this response. Meanwhile, utility of the glucose polymer over glucose or maltodextrin in energy beverages appears limited.