New research suggests that probiotics may offer an alternative treatment option for depression and other psychiatric disorders, examining the effect of the so called “psychobiotics,”  created as recent studies have begun to explore a possible link between probiotics and behavior.
Several preclinical studies showed a link between specific probiotics and beneficial behavioral effects, overall one in which rats with depressive behaviors resulting from maternal separation displayed normalized behavior and an improved immune response after ingesting the Bifidobacterium infantis probiotic.

We have, in adult age, approximately 1 to 2 kg of bacteria, several in the intestine, capable of producing hundreds of essential chemicals, like  neuroactive substances such as gamma-aminobutyric acid [GABA] and serotonin, which act on the brain-gut axis. Infact in a preclinical studies examined, mice that ingested L rhamnosus showed reduced anxiety scores and “altered central expression” on both the GABA type A and type B receptors. Others authors highlighted the link between immunity and bacteria, through the action of the systemic cytokines that act directly on the brain and suggested that might be an anti-inflammatory mechanism.
Although healthy aging is associated with a diverse range of these organisms, individuals who age in an unhealthy manner have a much less diverse range of bacteria.

These studies suggest that depression is also associated with an alteration in the microbiota. “Psychobiotics” are good bacteria that have the potential to increase microbial diversity and treat the symptoms of depression.
Another study show that a group of volunteers who received Lactobacillus helveticus  plus B longum for 30 days reported significantly lower stress levels than those who received placebo, as well as significantly reduced urinary free cortisol levels. Another study of 124 volunteers (mean age, 61.8 years) showed that those who consumed probiotic-containing yogurt for 3 weeks had significantly improved mood compared with those who received placebo.

An other study show us that in the human group with the chronic fatigue syndrome those who consumed an active strain of L casei 3 times a day had significantly higher improvement scores on anxiety measures than did those who received matching placebo.
The investigators have provided “a comprehensive review of recent compelling research into the microbiome-gut-brain axis and summarized the evidence for the anxiolytic and antidepressant action of Bifidobacteria or Lactobacilli in rodents and humans after their ingestion as live cultures,
The field needs to wait for large-scale, placebo-controlled trials to provide definitive evidence of benefit and to detect which probiotics have “psychobiotic” potential.