Effects of Milk-based Drinks on Gut Microbiome, Sleep and Cardiometabolic Markers

The gut microbiome is recognized as a key regulator of host health, influencing various physiological processes. Dysbiosis of the gut microbiome has been implicated in a range of adverse health outcomes, including disruptions in sleep architecture and impairments in cardiometabolic function. There is growing interest in identifying dietary interventions that can modulate gut microbiota composition and functionality. In particular, the consumption of fermented foods, such as kefir, has emerged as a potential strategy for promoting microbial homeostasis and improving health outcomes This study conforms to a randomised, double-blind 2-arm crossover design. Participants will consume either Kefir (original flavour) or milk. Each arm will involve daily consumption of the drink for 4-weeks with a 4 week washout before crossing over to the opposite condition. Drinks will be administered in a counterbalanced order to minimise potential order effects. The primary outcome of this study is a 5% change in LDL based on a previous study (Bellikci-Koyu et al., 2022). Assuming type I error probability α = 0.05 and power of 80%, and effect size of 0.2 G\*power calculated that 32 participants would need to be recruited. To account for potential drop out and balanced randomization, we will aim to recruit 40 participants. Participants will be recruited through the use of posters around Sheffield Hallam University and the University of Leeds, through emails to staff and students, and contacts at surrounding universities. Potentially eligible participants will be identified through the use of a recruitment questionnaire before being invited to a screening visit for full consideration for the study. All participants will provide written informed consent before participating. A linear mixed model analysis will be used to assess the effect of kefir on outcome parameters.