α-Cyclodextrin supplementation improves endurance exercise performance and reduces post-exercise fatigue in human males: a randomized, double-blind, placebo-controlled, parallel-group study

α-Cyclodextrin (αCD), a cyclic hexasaccharide composed of six glucose units, is not digested in the small intestine but is completely fermented by gut microbes. Recently, we have reported that αCD supplementation for nonathlete men improved their 10 km biking times. However, the beneficial effects of αCD on exercise are not yet fully understood. Therefore, we conducted a randomized, double-blind, placebo-controlled, parallel-group study to confirm the reproducibility and obtain additional data, employing a larger sample size and a greater αCD dose than that used in our previous study. Age, body mass index, estimated V̇O₂ max, and <i>Bacteroides uniformis</i> cell number in feces were used as stratifying factors. Eighty-one healthy nonathlete men aged 20 to 49 years who had exercise habits received a placebo (n=42) or αCD (1 g/day; n=39) for 9 weeks. Similar to our previous study, αCD supplementation significantly improved endurance exercise performance (10 km biking time trial) compared with the placebo (placebo=1,126.4 ± 133.6 s, αCD=1,073.2 ± 116.7 s, p=0.016). In addition, we observed a significantly reduced visual analog scale score for post-exercise fatigue (placebo=59.0 [46.3-54.3] mm, αCD=48.8 [37.0-50.3] mm, p=0.043). The heart rate increase was lower in the αCD group than in the placebo group during exercise (placebo=152.3 ± 11.1 bpm, αCD=144.2 ± 16.3 bpm, p=0.016). These results indicate that αCD supplementation improves endurance exercise performance and reduces post-exercise fatigue in nonathlete men.