Glucose‐fructose likely improves gastrointestinal comfort and endurance running performance relative to glucose‐only

This study aimed to determine whether glucose‐fructose ( GF ) ingestion, relative to glucose‐only, would alter performance, metabolism, gastrointestinal ( GI ) symptoms, and psychological affect during prolonged running. On two occasions, 20 runners (14 men) completed a 120‐min submaximal run followed by a 4‐mile time trial ( TT ). Participants consumed glucose‐only (G) or GF (1.2:1 ratio) beverages, which supplied ∼ 1.3 g/min of carbohydrate. Substrate use, blood lactate, psychological affect [Feeling Scale ( FS )], and GI distress were measured. Differences between conditions were assessed using magnitude‐based inferential statistics. Participants completed the TT 1.9% (−1.9; −4.2, 0.4) faster with GF , representing a likely benefit. FS ratings were possibly higher and GI symptoms were possibly‐to‐likely lower with GF during the submaximal period and TT . Effect sizes for GI distress and FS ratings were relatively small ( C ohen's d  = ∼0.2 to 0.4). GF resulted in possibly higher fat oxidation during the submaximal period. No clear differences in lactate were observed. In conclusion, GF ingestion – compared with glucose‐only – likely improves TT performance after 2 h of submaximal running, and GI distress and psychological affect are likely mechanisms. These results apply to runners consuming fluid at 500–600 mL/h and carbohydrate at 1.0–1.3 g/min during running at 60–70% VO 2peak .