The gut-brain axis refers to a bidirectional communication between the central and the enteric nervous system. It has the potential to influence emotional and cognitive centres in the brain directly from the intestinal neurological environment.
Besides neural influence also endocrine, immune and humoral moderators are being identified (e.g. serotonin or gamma-aminobutyric acid). Possible applications of these new insights may include autism, anxiety and depressive disorders, as well as Parkinson and Alzheimer diseases (Dinan & Cryan 2017a, Dinan & Cryan 2017b).
While a lot of the initial research on the use of probiotics to improve mood and/or stress was done on animals, there are more and more studies that show an effect in humans and the term “psychobiotics” has even been coined, referring to possible probiotics that could have an effect on mood and depression (Dinan et al. 2013).
Studies conducted using L. casei Shirota has thus far focused on mood in individuals with chronic fatigue syndrome (Rao et al. 2009) and healthy adults (detailed below). There have also been double-blind placebo-controlled trials conducted in Japan than have shown positive effects of consuming L. casei Shirota for eight weeks prior to an academic exam on stress-induced abdominal dysfunction, stress markers (psychological and physiological), sleep quality and the composition of the gut microbiota (Kato-Kataoka et al. 2016a, Kato-Kataoka et al. 2016b, Takada et al. 2017).
Study: Gut-Brain Axis
Effect on mood and cognition (in healthy adults) - Benton et al. (2007) Eur J Clin Nutr 61:355-361
Method: This double-blind placebo-controlled study conducted in the UK involved 132 healthy adults (mean age: 61.8 yrs) living in the community. Every day for three weeks, the volunteers drank one fermented milk drink containing L. casei Shirota (minimum 6.5 x 109 CFU) or a milk-based placebo of similar colour and taste. Mood and cognition was assessed throughout the drinking period.
Results: After 20 days, the mood in those who were more depressed at baseline (the bottom third of the participants based on the profile of mood states) had significantly improved (P<0.04).