Building on the known relationship between the gut microbiome and brain function, researchers at the University of Illinois at Urbana-Champaign set out to determine effects of a four-week treatment on negative mood states, stress and memory performance in healthy adults.
“Given the current standing of the literature, we hypothesized that consumption of a fermented dairy beverage with probiotics would alter the gut microbiota, decrease cortisol concentrations and depressive symptoms, and improve hippocampal-dependent relational memory,” the authors of the study stated.
While previous research provides some understanding of communication along the gut-brain axis through the hippocampus, the researchers noted the scarcity of studies on how probiotic consumption affects cognition and mental health in healthy populations.
Twenty-six participants, between the ages of 25 and 45 and free of gastrointestinal and mental illness, were divided into two sub-groups.
Initially, the first sub-group received eight-ounce daily portions of fermented dairy with active kefir cultures containing 12 probiotics (Lactobacillus lactis, L. rhamnosus, Streptococcus diacetylactis, L. plantarum, L. casei, Saccharomyces florentinus, Leuconostoc cremoris, Bifidobacterium longum, B. breve, L. acidophilus, B. lactis, L. reuteri). The second was given eight ounces of lactose-free 1% low-fat milk as control. After a washout period of at least two weeks, the groups switched beverages with testing prior to and after each period.
Researchers evaluated hippocampal-dependent relational memory through a spatial reconstruction task, with misplacement and object-location binding as error metrics. Participants self-reported negative mood states using the Depression Anxiety Stress Scales-42 (DASS-42), while urine samples were analyzed for the presence of urinary-free cortisol (UFC) as a biomarker of stress. Fecal microbiota composition was assessed using 16S rRNA.
No links to microbiota or effects on negative moods
Despite recording a 235% increase in probiotic Lactobacillus and improved relational memory, the research team could establish no correlation between the two. In addition, the trial did not reveal the expected effects on stress, depression and anxiety – the primary outcome measure of the study.
“Our results revealed a novel finding of an improvement in relational memory function following consumption of a fermented beverage containing probiotics,” the study concluded.
“However, there were no significant effects on participants’ self-reported stress, depression, and anxiety scores, or UFC concentrations. Further, the changes in Lactobacillus were not associated with changes in the outcomes of interest. Therefore, while consumption of fermented dairy beverage benefitted relational memory performance, these benefits were unrelated to changes in gut microbiota.”
Looking forward, the authors call for a double-blind study on a larger sample of healthy adults and more sensitive assessments of biomarkers related to stress, gastrointestinal health, and hippocampal function.
Source: Nutritional Neuroscience
Published online ahead of print: doi: 10.1080/1028415X.2022.2046963
“Consumption of a fermented dairy beverage improves hippocampal-dependent relational memory in a randomized, controlled cross-over trial”
Authors: Corinne N. Cannavale et al.