<b>Metabolic and Endurance Responses to Highly Branched Cyclic Dextrin with or without Protein During Soccer-Specific Intermittent Exercise</b>(data and figure)

Abstract Background: Soccer match play progressively increases reliance on rapid carbohydrate turnover, while opportunities to ingest fluid and nutrients are largely confined to brief periods before kick-off and during the half-time interval. Highly branched cyclic dextrin (HBCD), a low-osmolality carbohydrate, may improve gastrointestinal tolerance and sustain exogenous carbohydrate delivery, and co-ingested protein (PRO) could further modulate metabolic regulation and fatigue. Methods: Eight male soccer players registered with the Korea Football Association completed a single-blind, randomized crossover trial with three conditions: placebo (PLA; water), HBCD alone (CHO), and isocaloric HBCD plus whey protein isolate (CHOP). Beverages (500 mL) were consumed in two equal doses before exercise and at half-time. Participants performed a treadmill-based, soccer-specific intermittent running protocol (six 15-min cycles) followed by a run-to-fatigue (RTF) bout at 80% V̇max. Respiratory exchange ratio (RER), carbohydrate and fat oxidation, heart rate (HR), rating of perceived exertion (RPE), digestive symptoms (DS), running time, and running distance were assessed using repeated-measures ANOVA with Tukey-adjusted pairwise comparisons. Results: Versus PLA, CHO produced higher RER and carbohydrate oxidation and lower fat oxidation in Cycle 6 (p < 0.05), indicating greater late-exercise carbohydrate reliance, but did not significantly improve RTF. CHOP lengthened time to exhaustion by ~120 sec compared with PLA (p < 0.05), with a similar, non-significant trend for running distance (p = 0.080), despite only modest differences in substrate use. HR, RPE, and DS were comparable among conditions, and gastrointestinal complaints remained low. Conclusion: A moderate HBCD dose before exercise and at half-time shifted substrate use toward greater carbohydrate dependence in the later stages of high-intensity intermittent running without additional cardiovascular or gastrointestinal strain, while co-ingestion of a small whey protein dose with isocaloric HBCD was associated with improved fatigue resistance in this soccer-specific setting.