A new study published in the journal Nutritional Neuroscience shows that fermented dairy consumption increases the presence of some gut microbiota and improves relational memory (the ability to remember arbitrary associations between objects or events) in healthy adults.
Relying on a known link between the gut microbiome and brain function, researchers at the University of Illinois decided to investigate the effects of a four-week treatment on memory performance, negative mood states, and stress in healthy adults.
The authors of the study stated that the initial hypothesis was that consuming fermented dairy beverages with probiotics would reduce cortisol levels and depressive symptoms by altering intestinal microbiota and improving hippocampal-dependent relational memory.
While understanding of the relationship between the gut-brain axis through the hippocampus has been provided by previous research, researchers noted the scarcity of studies on how probiotic consumption affects cognition and mental health in a healthy population.
Study details
26 participants aged 25-25 years, healthy and free of mental and gastrointestinal illness were divided into two groups. The first group was required to consume eight ounces of fermented dairy products per day with active kefir containing 12 types of probiotics, while the second group consumed eight ounces of 1% low-fat lactose-free milk as a control. After a period of at least two weeks, the groups changed the drinks by experimenting before and after each period.
Researchers evaluated hippocampal-dependent relational memory through a spatial reconstruction task. Participants reported their 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. Moreover, the composition of fecal microbiota was examined using 16S rRNA.
The results showed that the consumption of fermented beverages had nothing to do with microbiota or negative moods
Despite a 235% increase in Lactobacillus probiotics and an improvement in relational memory, the research team found no association between the two. In addition, the study did not show the expected effects on stress, depression, and anxiety (the primary outcome measure of the trial).
In general, the results of the study showed new findings of improvement in memory performance after consuming a fermented beverage containing probiotics. However, fermented beverage consumption had no significant effect on the stress, depression, and anxiety reported by the participants themselves as well as the UFC concentration.
In addition, there was no association between changes in Lactobacillus and changes in outcomes of interest. Thus, while the consumption of fermented dairy beverages benefitted relational memory, these benefits have nothing to do with changes in the gut microbiota.
Researchers say a more comprehensive study with a larger sample and careful assessment through biomarkers related to gastrointestinal health, stress, and hippocampal function is needed.
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