Acute Milk-Protein Intake Enhances Pupil-Linked Executive Function and Esports Performance During Prolonged Play

Abstract Prolonged esports play induces cognitive fatigue that is not fully captured by subjective awareness, motivating practical, non-stimulant nutritional strategies supported by objective physiological markers. We here tested whether acute milk protein intake attenuates fatigue-related physiological responses during prolonged esports play and supports subjective state, executive control, and in-game performance. In a randomized, single-blind (assessor-blind), energy-matched controlled crossover study, 15 healthy young adults with esports experience completed two sessions in which they consumed either a milk protein drink or an energy-matched apple juice control before a 3-h virtual soccer task. Physiological measures included pupillometry during gameplay, salivary cortisol, continuous interstitial glucose monitoring, and heart rate. Subjective ratings (VAS) and executive function (flanker task) were assessed across post-ingestion time points, and in-game performance metrics were aggregated within hourly gameplay blocks. Milk protein intake was associated with a coherent pattern of physiological advantages, including larger pupil diameter during gameplay, smoother interstitial glucose dynamics, and lower salivary cortisol, while heart rate showed time-dependent changes without a clear condition effect. These physiological changes co-occurred with higher enjoyment and lower hunger, improved flanker performance, and condition-dependent improvements in in-game performance, most notably higher shot success rate. Additionally, pupil diameter during gameplay was associated with inhibitory-control efficiency on the flanker task. These findings suggest that acute milk protein intake may serve as a practical, non-stimulant nutritional strategy to sustain physiological state and cognitive–behavioral performance during prolonged esports (virtual soccer) play. Highlights – Prolonged esports play models modern digital cognitive activity and cognitive fatigue. – Acute milk protein intake increases pupil diameter during prolonged esports play. – Interstitial glucose dynamics are smoother and salivary cortisol is lower with milk protein. – Enjoyment increases and hunger decreases during 3 h of virtual soccer play. – Executive function and in-game performance improve, most notably shot success rate. Competing Interest Statement This study was funded by the Meiji Co., Ltd. C.O. and K.N. are employees of Meiji Co., Ltd. Authors affiliated with Meiji Co., Ltd. contributed to study design, data interpretation, and manuscript preparation. The funder had no role in data collection, data analysis. The academic authors had full access to all data and take responsibility for the integrity of the data and the accuracy of the analysis.