It is still early days in the field of gut microbiome research, and while an assortment of research is beginning to draw compelling connections between our gut bacteria population and our mental health, there are still plenty of unanswered questions. For example, can anxiety disorders be treated by simply altering a person's microbiome? And if so, what is the best way to change one's gut bacteria – simply altering a daily diet or consuming probiotics?

To try and answer some of those questions, a team of a Chinese researchers conducted a meta-study incorporating 21 published studies and over 1,500 subjects. About two thirds of the studies were investigating the effects of probiotics on the microbiome, while the other seven studies looked at non-probiotic microbiome interventions such as dietary changes or non-probiotic supplements. All 21 studies incorporated some kind of metric to measure anxiety symptoms.

The results interestingly found only 36 percent of the probiotic trials were found to successfully reduce symptoms of anxiety, whereas 86 percent of the non-probiotic interventions were effective. The researchers subsequently conclude, "although we can regulate the intestinal flora in two ways, the non-probiotic intervention is significantly better than the probiotic intervention."

The study hypothesizes three possible reasons why non-probiotic microbiome interventions may be more effective than probiotic interventions. First, it is suggested that as gut bacteria is mostly fueled by the food we eat, it is clear that diet can fundamentally regulate the growth of different bacterial populations. Secondly, the researchers note the 14 probiotic studies examined used a diverse array of bacterial species from study to study, resulting in different microbiome effects. Finally, it is hypothesized that the short duration of the majority of the studies, often just one or two months, may be too short for directly imported probiotic bacteria to take hold and significantly alter the microbiome.

The meta-study is undeniably fascinating but its conclusions are in no way definitive, primarily due to the major lack of heterogeneity across the collected studies. Not only did all the examined studies have different research design types but they did not even have consistent measurement metrics. For example, while all studies did include some kind of self-reported anxiety metric, there were over half a dozen different questionnaire scales utilized, making it nearly impossible to generalize a singular measure of anxiety improvement from study to study.

Alongside this problem, the meta-study also blended studies looking at patients with chronic diseases alongside studies focusing on healthy patients. Inflammatory bowel disease, obesity and fibromyalgia were all chronic conditions associated with anxiety symptoms in the studies, however, it is unclear whether an IBS patient with anxiety can be reasonably equated with a healthy subject with anxiety.

Nevertheless, the researchers do reasonably note all the limitations inherent to this particular meta-study, and clearly suggest, "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."

And, despite the need for further clinical work to clear up some of these issues, there is a growing body of research questioning the efficacy and benefits of probiotic supplements. From a recent finding that probiotics can evolve in the gut resulting in a negative influence on its host, to the discovery they can grow out of control in the intestine and cause bloating and brain fogginess, it is fair to suggest that simple, healthy dietary interventions may be the safest and most effective way to nurture a healthy microbiome.

The new research was published in the journal General Psychiatry.

Source: BMJ via EurekAlert