Plain language summary
Gut microbiota may be able to augment an individual’s mood, brain processing and cognition. Supplements containing live bacteria or a diet high in fibre which act as a substrate for beneficial gut bacteria may be of benefit to individuals with depression or mental illness. This 4-week randomised control trial aimed to determine the effect of a probiotic containing several different gut bacteria species on emotional processing and cognition in people with mild to moderate depression. The results showed that compared to placebo, probiotic intake increased empathy with others and improved some but not all aspects of cognition. Probiotic intake did not affect biological measures of stress but did improve feelings of depression. It was concluded that multispecies probiotics may change the emotional processing of people with depression. This study could be used by healthcare professionals to understand that the use of probiotics may be a good option to reduce the risk of people with mild to moderate depression developing a major depressive disorder.
BACKGROUND The potential antidepressant properties of probiotics have been suggested, but their influence on the emotional processes that may underlie this effect is unclear. METHODS Depressed volunteers (n = 71) were recruited into a randomised double-blind, placebo-controlled study to explore the effects of a daily, 4-week intake of a multispecies probiotic or placebo on emotional processing and cognition. Mood, anxiety, positive and negative affect, sleep, salivary cortisol and serum C-reactive peptide (CRP) were assessed before and after supplementation. RESULTS Compared with placebo, probiotic intake increased accuracy at identifying faces expressing all emotions (+12%, p < 0.05, total n = 51) and vigilance to neutral faces (mean difference between groups = 12.28 ms ± 6.1, p < 0.05, total n = 51). Probiotic supplementation also reduced reward learning (-9%, p < 0.05, total n = 51), and interference word recall on the auditory verbal learning task (-18%, p < 0.05, total n = 50), but did not affect other aspects of cognitive performance. Although actigraphy revealed a significant group × night-time activity interaction, follow up analysis was not significant (p = 0.094). Supplementation did not alter salivary cortisol or circulating CRP concentrations. Probiotic intake significantly reduced (-50% from baseline, p < 0.05, n = 35) depression scores on the Patient Health Questionnaire-9, but these did not correlate with the changes in emotional processing. CONCLUSIONS The impartiality to positive and negative emotional stimuli or reward after probiotic supplementation have not been observed with conventional antidepressant therapies. Further studies are required to elucidate the significance of these changes with regard to the mood-improving action of the current probiotic.