Gut microbiota influence many aspects of host health including immune, metabolic and gut health. We examined the effect of a putative prebiotic, consumed daily as a fermented whey concentrate (FWC) rich in (L+)-lactic acid in 18 healthy men (n=5) and women (n=13) in free-living conditions. Objective: The aims of this 6-week pilot trial were to (i) identify changes in the gut microbiota composition and faecal short chain fatty acid (SCFA) profile, and (ii) to monitor changes in glucose homeostasis. Results: Total faecal SCFA (mM) concentration remained constant throughout the intervention. Proportionally, there was a significant change in the composition of different SCFAs compared to baseline. Acetate levels were significantly reduced (-6.5%; p<0.01), coupled to a significant increase in the relative amounts of propionate (+2.2%; p<0.01) and butyrate (+4.2%; p<0.01), respectively. No changes in the relative abundance of any specific bacteria were detected. No significant changes were observed in glucose homeostasis in response to an oral glucose tolerance test. Conclusion: Daily consumption of a fermented whey product led to significant changes in detected fecal SCFA metabolite profile, indicating some prebiotic activity. These changes did not result in any detectable differences in microbiota composition. Future work is required to identify the biological mechanisms underlying the observed changes in microbiota activity, and to explore if these processes can be harnessed to favorably impact host health. Clinical trial registration: www.clinicaltrials.gov, identifier NCT03615339; retrospectively registered on 03/08/2018.