Effects of continuous isomaltulose-containing gummy intake on interstitial glucose and salivary hormones during an 18-hole golf round: a randomized, double-blind controlled pilot study.
BACKGROUND: Golf is a prolonged, moderate-intensity sport requiring sustained physiological stability to manage cumulative stress and maintain performance. Although carbohydrate intake is commonly used to reduce fatigue, rapidly absorbed sugar-induced rapid blood glucose fluctuations may induce volatile arousal and latent metabolic stress. Isomaltulose, a slow-digesting disaccharide, provides a steadier glucose supply compared with sucrose. This exploratory pilot study examined the effects of isomaltulose intake on physiological stress markers, glycemic dynamics, and subjective responses during a competitive 18-hole golf round. METHODS: Twenty-three male collegiate golfers were randomized to either the isomaltulose group (ISO; n = 12) or the sucrose group (CON; n = 11) in a double-blind controlled trial. Participants consumed gummies containing isomaltulose or sucrose immediately after each hole (12.1 g carbohydrate per hole; total carbohydrate intake: 217.5 g). Primary outcomes were salivary stress markers [cortisol, testosterone, and dehydroepiandrosterone sulfate (DHEAS)] levels. Secondary outcomes included interstitial glucose concentration measured via continuous glucose monitoring, subjective assessments (i.e. sleepiness, relaxation, and concentration), and golf performance (18-hole score). Between-group comparisons at each time point were conducted using planned Welch's t-tests. RESULTS: No significant between-group differences were observed for 18-hole score (p = 0.38) or mean interstitial glucose concentration (p = 0.20). However, exploratory analyses revealed distinct hormonal variations; salivary DHEAS and testosterone levels were higher in the ISO group during the latter half of the round (p < 0.05), whereas both declined in the CON group. Regarding glycemic variability, the ISO group demonstrated a more stable glucose profile with a medium effect size for lower standard deviation (ISO: 14.7 ± 1.9 vs. CON: 16.7 ± 4.6 mg/dL; d = 0.58), although this difference was not significant. Conversely, subjective outcomes diverged; the CON group reported significantly greater subjective arousal (wakefulness and relaxation) (p < 0.01) relative to the ISO group. CONCLUSIONS: In conclusion, continuous intake of isomaltulose-containing gummies during an 18-hole golf round was associated with differences in selected physiological markers, including DHEAS and testosterone concentrations. However, these findings were not accompanied by improvements in objective golf performance outcomes compared with sucrose-containing gummies. Isomaltulose may influence glycemic dynamics and hormonal responses during prolonged golf play; however, the practical significance of these effects remains exploratory. Further studies with larger sample sizes and appropriate repeated-measures frameworks are needed to determine whether such physiological changes translate into meaningful performance or recovery benefits.