Can Improved Gut Health Ease Symptoms of Depression?

A small study suggests that people with major depressive disorder can benefit from taking a probiotic as part of their treatment plan.

Scientists believe that gut health can impact mental health. A small pilot study published June 14 in JAMA Psychiatry posed the question: Can improving gut health ease depression? 

The researchers found that people with major depressive disorder (MDD) who took probiotic supplements (containing beneficial bacteria) along with their antidepressant medication had greater improvements in their symptoms than those on placebo. 

The findings of this pilot study are an important step in understanding the role of probiotics in mood and mental health, says the study’s first author, Viktoriya Nikolova, a researcher at the Institute of Psychiatry, Psychology, and Neuroscience at King’s College London. 

“We observed strong effects across both depression and anxiety outcomes. The strongest effect was observed for anxiety scores, which suggests that probiotics may be most beneficial to those people with MDD who also have anxiety — however, this finding needs to be verified in larger trials,” says Nikolova. 

The Gut Is Our ‘Second Brain’

The body has several distinct so-called microbiomes, composed of trillions of bacteria and other microorganisms that are involved in our overall health.

There are microbiomes on the skin and in the mouth, but the most important one is in the digestive system, often called the gut microbiome, according to the University of Chicago.

There is increasing evidence that the dynamic community of microorganisms inhabiting the gut has a role to play in what’s called the gut-brain axis. When something affects the brain, it can also impact the gut, and vice versa. 

Scientists believe that communities of microorganisms in the gut interact with the central nervous system by regulating brain chemistry and influencing hormones related to stress response, anxiety, and memory. 

In fact, the gut is sometimes referred to as a “second brain” because it produces many of the same neurotransmitters the brain does, such as serotonin and dopamine, which both play a key role in regulating mood. According to the American Psychological Association, gut bacteria produce about 95 percent of the body’s serotonin, the chemical messenger that affects mood, sleep, digestion, and sexual desire. 

Study Included 49 Adults With Major Depressive Disorder

The double-blind, randomized, placebo-controlled study was intended as an initial exploration into whether improving gut health through the use of probiotics could act as a new pathway for improving mood and mental health.

Participants were 49 adults who had been diagnosed with major depressive disorder and whose depression wasn’t sufficiently managed with their current prescription antidepressant (92 percent of participants were taking a selective serotonin reuptake inhibitor, or SSRI). The average age was 31 years old, 80 percent were women, and most were white. 

Subjects were randomly divided into two groups: 24 people received four daily capsules of the commercial probiotic supplement Bio-Kult Advanced, containing 14 strains of bacteria. (Note: The manufacturer of Bio-Kult, ADM Protexin, provided funding for this research.) The remainder were given an identical placebo. 

The probiotic blend contains strains from species that had shown psychoactive potential in people with major depressive disorder, as well as efficacy in other conditions affected by the gut-brain axis, including IBS and migraine, says Nikolova.

The probiotic blend was shown to positively impact mood in people with self-reported low mood in a study published in February 2022 in Psychological Medicine

Probiotic Supplements Showed Strongest Benefits in Reducing Anxiety

Over the course of eight weeks, both groups demonstrated improvement in their symptoms, but the probiotic group saw greater improvements beginning at week 4. Meaningful reported improvements in depressive and anxiety symptoms compared with placebo were seen in four different gold-standard rating scales.

About 3 in 5 People With Major Depressive Disorder Don’t Fully Respond to Antidepressants

The pilot study is one of the first trials in a Western population to show that probiotics are well-tolerated, with no side effects, and have positive effects on mental health in adults with depression currently taking antidepressants, according to the authors.

About three in five people with major depressive disorder do not fully respond to first-line treatments, and about one-third continue to have symptoms even with further treatment, they noted. 

Larger Studies Are Needed to Confirm Findings

The number of participants in this clinical trial means it’s not possible to draw any definitive conclusions about the outcome, says Emeran A. Mayer, MD, a distinguished research professor of medicine at UCLA Health, the founding director of the Goodman-Luskin Microbiome Center, and the author of The Mind-Gut Connection.

These findings support earlier studies about the demonstrated benefits of psychobiotics (microbial organisms with a demonstrated mental health benefit), says Dr. Mayer. “Many of these studies have evaluated probiotics on patients with nonclinical depression, and were also underpowered,” he adds.

A larger trial, “like the trials the pharmaceutical industry has to perform to get approval for a pharmacologic treatment of MDD,” is needed to determine if probiotics are an effective intervention, says Mayer. “This would require the enrollment of a minimum of 500 patients,” he says. 

Interested in Taking a Probiotic?

If a person with major depressive disorder is interested in taking a probiotic, should they talk with their doctor? 

“The majority of my patients are already on some probiotic. Some of them feel it is beneficial, a lot of them don’t know,” says Mayer.

Because there are minimal-to-no known side effects, Mayer encourages his patients to continue their probiotic or, preferably, to include fermented foods in their diet that are naturally high in beneficial bacteria.

Top fermented foods include kefir, plain yogurt, fermented vegetables, miso, sauerkraut (choose refrigerated), and kimchi, according to UMass Chan Medical School Center for Applied Nutrition.

“I also recommend an anti-inflammatory diet, like the traditional Mediterranean diet, because there is some evidence for its effectiveness as an adjuvant treatment. As few doctors are experts in this area, I don’t believe a patient needs to consult their doctor about probiotics,” says Mayer.