Psychobiotics - gut bacteria changing our brains?

Walking through the aisles of my local health food store, the Williamson Street Co-op, I’ve often been tempted by the claims of exotic yoghurts and “probiotic” drinks like Kefir, that contain strains of Lactobacillus and a number of other “good” bacteria. It turns out a number of these bugs produce and release into our gut neuroactive compounds such as GABA, an inhibitory neurotransmitter, and serotonin, a mood regulator. Dinan et al. do a review article on what they term psychobiotics (organisms that alleviate psychiatric illness)

Here, we define a psychobiotic as a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness. As a class of probiotic, these bacteria are capable of producing and delivering neuroactive substances such as gamma-aminobutyric acid and serotonin, which act on the brain-gut axis. Preclinical evaluation in rodents suggests that certain psychobiotics possess antidepressant or anxiolytic activity. Effects may be mediated via the vagus nerve, spinal cord, or neuroendocrine systems. So far, psychobiotics have been most extensively studied in a liaison psychiatric setting in patients with irritable bowel syndrome, where positive benefits have been reported for a number of organisms including Bifidobacterium infantis. Evidence is emerging of benefits in alleviating symptoms of depression and in chronic fatigue syndrome. Such benefits may be related to the anti-inflammatory actions of certain psychobiotics and a capacity to reduce hypothalamic-pituitary-adrenal axis activity. Results from large scale placebo-controlled studies are awaited.