Gut bacteria regulation a target for easing anxiety, suggests review

A team of Chinese scientists found that over half of the studies, which featured probiotic and non-probiotic interventions could regulate the intestinal microbiota and in turn anxiety symptoms.

Further analysis found non-probiotic interventions to be more effective than probiotic interventions as the authors suggest a changing diet (a diverse energy source) as having more of an impact on gut bacteria growth than introducing specific types of bacteria in a probiotic supplement.

“For patients with somatic diseases who are not suitable for the application of psychiatric drugs for anxiety treatment, probiotic methods and/or non-probiotic ways like low FODMAPs can be applied flexibly according to clinical conditions,”​ said the team from Shanghai Jiao Tong University School of Medicine.

“However, there are still some studies showing that the effect of regulating intestinal flora to improve anxiety symptoms is limited. ​

“Therefore, more relevant clinical intervention studies should be carried out with the unified anxiety assessment scales and statistical methods being used to clarify the relationship between intestinal flora adjustment and improvement of anxiety symptoms.”​

Gut-brain axis​

A number of studies have shown that intestinal flora can control communication between the gut and the brain via the gut-brain axis, which includes the nervous, immune and endocrine system.

When intestinal flora is affected, a series of changes in physical and/or mental symptoms can occur.

Despite a number of animal studies demonstrating that germ-free mice pretended to have anxiety-related behaviours that were changeable via gut microbiota regulation, there is no agreement on whether anxiety symptoms can be improved by regulating gut microbiota.

The University team shortlisted 21 studies that altogether looked at 1,503 people. From this selection 14 studies selected probiotics as interventions to manage the intestinal microbiota (IRIFs) environment. Additionally, seven studies used non-probiotic ways, such as adjusting daily diets.

The research team discovered that probiotic supplements used in seven of the studies contained only one type of probiotic.

Two studies used products that contained two kinds of probiotics, and the supplements used in the other five studies included at least three kinds.

In total 11 of the 21 studies resulted in a positive effect on anxiety symptoms. This meant just over half (52%) of the studies investigated suggested this approach had a meaningful impact.

Additionally, out of the 14 studies that included probiotics, over a third (36%) found them helpful in reducing anxiety symptoms.

Those six studies out of the remaining seven that included a non-probiotic as an intervention found an 86% effectiveness rate.

Finally, non-probiotic interventions were also more effective in the studies that used interventions to regulate intestinal microbiota (IRIF) alone.

Analysis of the studies that used using IRIF, found 80% of those to be effective when using non-probiotic interventions. In total 45% of studies were effective when using probiotic ways.

Survival of the fittest ​

Along with a switch in energy source via a diet change, the research team highlighted studies that used probiotic interventions as ones where “the probiotic species were diverse and there were survival competitions in implanted flora and primitive flora, which may lead to not all the imported probiotics being effectively implanted.” ​

“Most intervention times of included studies were 4–8 weeks. This might be too short to significantly increase the abundance of the imported microbiota, so that the subjects’ original intestinal flora could not be effectively adjusted,”​ the team added.

Positive outcomes were balanced out with the review’s limitations that included differences in the research design types, subjects, interventions and anxiety assessment scales of the 21 articles included,

“Fifty per cent of the 10 studies on IBS showed that the interventions were effective,”​ the study said.

“Therefore, for patients with IBS, more studies are needed to verify whether it is possible to clinically treat the anxiety symptoms of patients with IBS by regulating intestinal flora.”​

Source: BMJ (General Psychiatry)​

Published online: doi.org/10.1136/gpsych-2019-100056​​

“​Effects of regulating intestinal microbiota on anxiety symptoms: A systematic review.”​

Authors: Beibei Yang, Jinbao Wei, Peijun Ju and Jinghong Chen