(CNN) — We have a heartbreaking experience, and then we have a clear feeling in our stomach.
Many of us instinctively feel the connection between our gut and our brain. That connection, and how the variety of bacteria that reside in our digestive tract – our microbiome – could help treat mental illness has become a field of interest to scientists in recent years.
A new review of the medical literature suggests that probiotics — foods or supplements that contain microbes that are believed to exert a positive influence on our gut — may help alleviate depression.
“This is good quality research, but it is a review of relatively preliminary data,” Allan Young, professor of mood disorders at King’s Institute of Psychiatry, Psychology and Neuroscience, told the London Science Media Center (SMC). College London.
So while this systematic review of the research literature supports the notion that prebiotics and probiotics may be helpful for people with anxiety and depression, more research is needed. These data justify conducting larger trials, ”said Young, who was not involved in the review.
Researchers from the University of Brighton and Croydon University Hospital in the UK analyzed 71 studies published between 2003 and 2019 that studied how probiotics and prebiotics, compounds that help probiotics to thrive, can help adults with disorders of depression and / or anxiety.
Only seven of those studies were considered robust enough to be included in the systematic review, but all showed “significant improvements” in measuring the effect of taking pre and probiotics compared to not receiving any treatment or taking placebos. While probiotic supplements, alone or in combination with prebiotics, may be linked to measurable reductions in depression, the possible contribution to decreased anxiety was not yet clear, according to the study.
The researchers said their review carried several caveats: none of the included studies lasted long and the number of participants in each case was small.
This made it difficult to draw firm conclusions about the overall effects, how long they lasted and whether there could be unwanted side effects associated with long-term use of probiotics, they said.
David Curtis, a retired consulting psychiatrist and honorary professor at University College London, said probiotics were unlikely to have an effect on mood.
“Although these published studies claim to show some benefits of probiotics in depression, we have no idea if there were other studies that did not show any effects that were not published,” he told the SMC.
“People with depression should seek medical advice and not try to be treated with dietary supplements, which have no proven benefit,” he added.
The review, which was published Monday in the magazine BMJ Nutrition, Prevention & HealthHe said exactly how probiotics could alleviate depression was unknown, but the researchers suggested they could have a dual effect.
First, probiotics can help reduce the production of inflammatory chemicals, such as cytokines, or they can help direct the action of tryptophan, a chemical that is considered important in the gut-brain axis in psychiatric disorders.
Second, people with depression often have other underlying conditions as well, such as impaired insulin production and irritable bowel syndrome, and probiotics can influence how a person experiences depression by alleviating these conditions.
However, the argument in favor of the use of probiotics in the treatment of digestive disorders is unclear.
For most digestive diseases, including conditions such as Crohn’s disease, ulcerative colitis, or irritable bowel syndrome, a review published last month by the American Gastroenterological Association (AGA) said it did not there is sufficient evidence to recommend the use of probiotics.
“We are still learning about the numerous and complex communication pathways between the brain and the intestine. It is certainly plausible that microbiome-targeted therapies can improve aspects of depression and anxiety by alleviating an individual’s gastrointestinal area, ”said Dr. Geoffrey Preidis, spokesperson for the association and pediatric gastroenterologist at the Baylor School of Medicine and Texas Children’s Hospital.
“AGA’s review of the current evidence base found insufficient evidence to recommend probiotics for irritable bowel syndrome at this time. However, future clinical trials will address this knowledge gap, so we must continue to evaluate the rapidly changing evidence in this exciting field, ”he said in an email.
Probiotics have become more popular as researchers have learned more about the role of our gut bacteria, or microbiome, in our gastrointestinal health, and why these supplements promise an effective way to alter the microbiome for our benefit.
The studies in the review looked at 12 probiotic strains, mainly Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium bifidum. One study looked at combined pre and probiotic therapy, while another looked at prebiotic therapy alone.
John Cryan, professor, chair of the Department of Anatomy and Neuroscience and principal investigator at the College of Food Pharmaceutical Center at Cork College University, said it was important to identify which strains had what effect.
“We know that strains really matter, and this review is unable to identify what is going on with specific strains that have beneficial effects,” he told SMC.
“As highlighted in this review, there is a great need for longitudinal studies for different psychobiotic strains and diets, both as independent and complementary therapies in anxiety and depression,” he added.