Psychobiotics is a term used in preliminary research to refer to live bacteria that, when ingested in appropriate amounts, might confer a mental health benefit by affecting microbiota of the host organism. Whether bacteria might play a role in the gut-brain axis is under research. However, as of 2018, there is a paucity of randomized controlled trials testing the effects of live, ingested bacterial strains on clear mental health outcomes, and those that have been done provide inconclusive results when viewed in aggregate.
In experimental probiotic psychobiotics, the bacteria most commonly used are gram-positive bacteria, such as Bifidobacterium and Lactobacillus families, as these do not contain lipopolysaccharide chains, reducing the likelihood of an immunological response. Prebiotics are substances, such as fructans and oligosaccharides, that induce the growth or activity of beneficial microorganisms, such as bacteria on being fermented in the gut. Multiple bacterial species contained in a single probiotic broth is known as a polybiotic.
The field of psychobiotics in humans is nascent, though there have been many studies in rodents demonstrating increased cognitive functioning, decreased anxiety, and decreases in stress related pathology. However, the human literature has yet to catch up with most rodent experiments, and has so far failed to produce a high number of well designed, randomized trials. Several recent reviews have highlighted the fact that there is a need for more diverse human studies, particularly because those that exist are often hard to compare and have contradictory outcomes.
- Lactobacillus helveticus
- Bifidobacterium longum
- Lactobacillus casei
- Lactobacillus plantarum
- Lactobacillus acidophilus
- Lactobacillus delbrueckii subsp. bulgaricus
- Bifidobacterium breve
- Bifidobacterium infantis
- Streptococcus salivarius
- Lactobacillus rhamnosus
- Lactobacillus gasseri
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