Pre-sleep alpha-lactalbumin and dietary protein interactions on sleep, mood, and cognition in athletes with sleep difficulties: a protocol for a factorial crossover randomised controlled trial

Abstract Background Athletes are often subjected to sleep disruptions due to factors including extensive training load and training hours. Insufficient sleep impairs several physiological and psychomotor functions essential for optimal recovery, performance, and injury prevention in athletes. With growing interest towards whole-food nutritional strategies, alpha-lactalbumin (ALAC), a whey protein from cow’s milk, presents promising potential for sleep improvements. ALAC contains high amounts of the amino acid tryptophan which promotes its availability to the brain and positively influences endogenous melatonin production. However, little is known about the effect of ALAC on sleep improvement in poor sleepers. Additionally, most previous interventions implemented a low-protein antecedent meal, posing potential concerns regarding its practical application. The present study aims to investigate whether ALAC supplementation improves sleep, mood, and cognition in athletes with sleep difficulties. In addition, this study will explore the effect of dietary protein interactions on the efficacy of ALAC. Methods This study protocol details a factorial crossover randomised controlled study recruiting twenty-four participants. Participants will be randomised into two-arms based on their diet allocations – habitual protein diet and lower-than-recommended protein diet. The study will be conducted as a field-based study, with participants visiting the laboratory for cognitive function tests at baseline and post-intervention. In a crossover manner, participants will consume both; ALAC and a placebo supplement, in a random order, while following their assigned diet. Primary outcomes include objective sleep quality measures. Secondary outcomes include urinary 6-sulfatoxymelatonin levels, mood, and cognitive function. Linear mixed models with fixed effects will be performed to analyse between treatments and diet group effects. Discussion The strengths of the present study include the primary focus of exploring ALAC supplementation for improving sleep in athletes with existing sleep difficulties. The implementation of a crossover design limits inter-individual variability and improves the efficiency of between treatment comparisons. Findings from the study will strengthen the current body of literature and provide further insights into the therapeutic potential of ALAC. Being a field-based study, compliance towards the study tasks might be lower compared to a controlled lab-based setting. Registry Australian New Zealand Clinical Trial Registry (ANZCTR), TRN: ACTRN12625001246471, Registration date: 10 November 2025.