New Study Links PTSD, Mediterranean Diet, and Gut Bacteria

A new study published in Nature Mental Health explored the complex relationship between post-traumatic stress disorder (PTSD) and gut health.

A Second Brain

The concept of the gut as a “second brain” or a “hidden organ” is an emerging focus in scientific research. As Harvard Associate Professor of Medicine, Yang-Yu Liu told Psychiatrist.com, the digestive tract plays a primary role in the enteric nervous system (ENS) found within the gut’s walls. In addition to housing innumerable colonies consisting of trillions of microorganisms, the gut also contains millions of neurons.

“Those neurons communicate with the central nervous system through channels like the vagus nerve which connects the brain to the gut,” he explained. “The gut microbiome has its own influence on the brain as well.”

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In fact, previous work suggests the gut produces about 90 percent of the body’s serotonin. Additionally, the microbiome independently creates its own neurotransmitters and other bioactive molecules that can cross the gut-brain barrier. All this points to an association between the gut and neurological and psychological functions. 

Intriguing Results

To test this theory, the study enrolled 191 women from the Nurses’ Health Study-II (NHS-II), which included the Mind-Body Study (MBS) and the PTSD Substudy. Based on a psychological assessment, researchers assigned participants to one of three groups: probable PTSD, exposed to trauma but no PTSD, and no trauma exposure. All the subjects submitted two sets of four stool samples, once at the beginning of the study and then again six months later. The researchers also compiled a detailed history of participants’ dietary habits. 

Results showed that BMI, depression, and the use of antidepressants had a strong association with the composition of the gut microbiome. A combination of these host factors seemed to interact in complex ways, suggesting  that they worked together to change the structure of the microbiome.

Dietary patterns also showed a correlation to the level and severity of trauma symptoms.

“We found that very interestingly, eating a Mediterranean diet was associated with less PTSD,” noted Liu, who is also a social scientist at Brigham and Women’s Hospital where the research was conducted. “Specifically, reduced consumption of red and processed meats, coupled with an increase in plant-based foods, was linked to lower levels of PTSD.” 

The researchers paid special attention to a particular bacteria species called Eubacterium eligens which stood out for its potentially protective role against PTSD symptoms; higher levels of E. eligens were consistently associated with fewer PTSD symptoms across multiple time points in the study.

The bacteria species also showed a positive relationship with healthier eating patterns commonly found in the Mediterranean diet. For example, eating raw carrots seemed to raise levels of E. eligens while the level of these beneficial bacteria dipped when subjects ate a lot of red or processed meat. 

A Good Start

As Liu explained, the presence of E. eligens seemed to be favorable for both for gut health and for mental health. Thriving colonies of the species were more common in people who ate healthier foods and less common in those with more severe PTSD symptoms. However, he was quick to point out that correlation does not necessarily translate to causation.

“This was an observational study so we can only say that we see gut changes associated with PTSD symptoms. We cannot say from this study that they caused them,” he said. 

The findings are just a start, Liu added. It’s work that opens the door to future research on how diet directly influences the gut microbiome, and in turn the microbiome influences mental health. Although the study’s conclusions require further validation, Liu said they raise the possibility that specific diets could either mitigate the symptoms of PTSD or even avoid its onset altogether following a traumatic event. 

“E. eligens might be a very strong candidate for a probiotic that works for PTSD prevention and arbitration,” he said. His team is already experimenting with animal models to develop a dietary supplement containing bacteria that could prove helpful to mental well-being.