For the past 10 years or so scientists have become more interested in how the gut acts an an influence on the brain.
Recent research shows that the bacteria in our digestive system can play a role in our mental health.
Supplements designed to increase the health promoting bacteria may have an anti anxiety effects.
Where as probiotic supplements are the bacteria themselves, prebiotics are the short chain carbohydrates that the ‘good’ bacteria feed on. Supplying these aids in their growth and proliferation.
A recent double blind controlled study looked at 45 healthy adults who took either prebiotics or a placebo (to act as control) every day for three weeks. At the end they were subject using a computerised battery of tests to see how individuals process emotionally charged worlds and facial expressions designed to assess the processing of emotionally salient information. 
The results show that those who took the prebiotics had paid less attention to negative information, and more towards positive information compared to the control group.
Biases in the processing of information, more vigilance to threatening and danger signs is greater in anxious individuals compared to non-anxious. Tests that show this are considered markers for anxiety and even depression.
Reductions in attentiveness to negative information and more towards the positive suggests individuals have become less anxious using this supplement.
Those subjects who took the prebiotic also had less cortisol in their saliva, a stress hormone linked to anxiety and depression.
It’s well known that the brain sends signals to the gut, but this research and others show this its a two way street of information. What happens is signals are sent from the gut to the brain affecting it’s function and therefore our own consciousness. Such a link has be noticed where patients with mental health problem also have issues with their digestive system. Fro example Irritable bowl syndrome, indigestion, coeliac disease and others.
There is now convincing evidence that our mental state is affected by our digestive tract which means what we eat is an important part of our mental health.
It’s something I learned in my nutrition education. That our diet has important and far ranging effects on us beyond the supplying of calories and macro or micronutrients.
It should be noted that the effective prebiotics were the Bimuno®-galactooligosaccharides, (B-GOS), not fructooligosaccharides (FOS).
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- Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers – Springer. [cited 2015 Feb 3]; Available from: http://link.springer.com/article/10.1007/s00213-014-3810-0/fulltext.html#CR12