In March of this year, researchers showed that a probiotic found in yogurt was able to reverse symptoms of anxiety and depression in mice. Now, in a small study involving 44 adults, investigators at McMaster University in Canada have shown a different probiotic can have the same effect in humans.

Increasingly, scientists are exploring the link between our guts and our brains, and finding that the two are very much linked. Earlier this year, researchers found that they could alter the gut microbiota by beaming people's' brains with magnetism, and last year, a study indicated that certain molecules in the gut can inhibit inflammation it the brain.

The McMaster research focussed on individuals with irritable bowel syndrome (IBS) which, the university says, is the most common gastrointestinal disorder in the world. The study split 44 adults into two groups. One group took the probiotic Bifidobacterium longum every day for ten weeks, while the other group took a placebo.

At six weeks, in the group taking the probiotic, 14 out of 22 participants (64 percent) had a lower depression score than the group taking the placebo. What's more, the researchers saw changes in brain areas associated with depression in the probiotic group when they observed them using functional MRI (fMRI) scans.

"The fMRI study showed decreased activity in the amygdala and other fronto–limbic regions of the brain, which are known to be involved in the control of mood, in the patients taking with probiotics compared to those taking placebo," Premysl Bercik told us. Bercik is an associate professor of medicine at McMaster and senior author on the study.

Of course, one theory is that the symptoms of depression went away in the study subjects taking the probiotic because their IBS symptoms also improved. So we asked Bercik about that, and he said that the effects of the probiotic treatment on mood lasted longer than the effects on the IBS symptoms – longer than the treatment was carried out, in fact.

"You are right," he told us, "the patients on probiotics also reported improvement in their IBS symptoms (adequate relief of symptoms) at the end of the probiotic treatment, but not four weeks later when the beneficial effect on depression was still present. So one can argue that the primary effect of this probiotic is on depression. Also, the amygdala is one of the important centers in processing abdominal pain so if the probiotic altered the function of this brain region, it could also improve the gut symptoms of IBS (the pain is the hallmark symptom of IBS)."

The study, which was carried out in conjunction with scientists from food giant Nestlé, has been published in the journal Gastroenterology.

Source: McMaster University