While many of the numerous health-improvement claims have yet to be supported scientifically, it has been claimed that micro-organisms do exert positive effects in intestinal tracts, particularly when used to counteract the effects of antibiotics, which kill both 'bad' and 'good' bacteria.
Over the past few years, studies have been undertaken to explore the possible impact of probiotics on behaviour. It is within this context that the concept of a psychobiotic has arisen.
Timothy Dinan and his colleagues from University College Cork in Ireland, define a psychobiotic as "a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness."
The gut microbiota, which contains approximately 1 kg of bacteria, can be modulated by diet and many other factors. It is not static and can change from day to day, starting at birth. Evidence has shown that even the form of delivery (vaginal versus cesarean) alters an individual's microbiota.
Dinan and his colleagues review one study that assessed the potential benefits of a specific probiotic, B. infantis, in rats displaying depressive behaviour due to maternal separation. The probiotic treatment normalized both their behaviour and their previously-abnormal immune response.
This preclinical study and others like it strongly support the hypothesis that probiotics have the potential to exert behavioural and immunological effects.
The study is published in Biological Psychiatry.