Feeding mice a mixture of different prebiotic ingredients led to less stress and anxiety. This could shed light on how different foods might alter the gut microbiome in humans.

There is no topic hotter in nutrition research at the moment than the gut microbiome. The microbiome is made up of all the resident bacteria, viruses and microbes that have colonised our gastrointestinal tract. Research teams are now looking into the link between gut microbiota and the brain and how this plays a role in regulating brain functions, particularly emotional processing and behaviour.

Coming out of the University College Cork in Ireland, a three week study in mice observed how two prebiotics in the diet can affect the growth of gut bacteria linked to stress, mood and behaviour. Prebiotics are the foods that feed beneficial gut bacteria. They love fibre – and lots of it.

Eating a mixture of different foods with different types of prebiotics in them can influence which bacteria are most active in the gastrointestinal tract. These bacteria in turn produce a range of different substances, some of which are linked to lowering stress and anxiety. One such substance is serotonin, the ‘feel-good’ neurotransmitter.

Serotonin is not just found in our brain. Over half the serotonin in our body is made in the intestinal tract. There is more than a passing connection between the gut and brain and the system of hormones and immune activity in the intestines is now recognised as an important regulatory system. Our gut can rightly be called our ‘second brain’.

Keeping mice happy with prebiotics

In this new study, the team fed mice two promising prebiotic ingredients called FOS (fructo-oligosaccharide) and GOS (galacto-oligosaccharide). FOS and GOS are non­digestible carbohydrates which reach the colon intact and are fermented by the colonic bacterial microflora. FOS and GOS are found naturally in a range of foods high in fibre such green vegetables, legumes, beans and Jerusalem artichokes.

Healthy mice fed a combination of the two prebiotics had measurable improvements in anxiety, cognition and stress-related behaviours when exposed to stressful conditions. There was more going on below the surface. Gene expression changed in key parts of the brain also. Finally, prebiotic-fed mice had lower levels of stress-induced hormones and immune factors. The team is planning to run human trials soon to see if prebiotics can produce similar stress-reducing results.

Melding together the fields of prebiotics, probiotics and mental health, a new research field is emerging: psychobiotics. A psychobiotic is a live organism that, when ingested in adequate amounts, produces a health benefit in people suffering from mental health issues.


Having the right mix of prebiotics and probiotics in the diet may be one way to support our mental health. The new research presented here strengthens the rationale of targeting gut microbiota for psychologicaL disorders. The best thing about the research is that foods high in prebiotics are already what are recommended for us to be eating lots more of for overall health. Improved mental health may be another benefit to add to the list.

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