Jars of various sizes full of fermented foods such as sauerkraut and kimchiShare on Pinterest
Adding fermented foods to your diet could have many health benefits. Rene de Haan/Stocksy
  • The foods we eat have an impact on our overall health.
  • A new study from APC Microbiome Ireland suggests that eating a diet rich in prebiotic and fermented foods can help people feel less stressed.
  • The researchers further found that such a “psychobiotic” diet also improved a person’s sleep quality.

We’ve all heard the old adage “you are what you eat.” Over the years, researchers have proved that to be true, showing the food a person chooses to eat can have a profound impact on their overall health.

Now, researchers from APC Microbiome Ireland at the University College Cork (UCC) in Ireland say changing to a diet high in prebiotic and fermented foods can help lower a person’s perceived stress levels and improve sleep quality.

This study was recently published in the journal Molecular Psychiatry.

According to Dr. John F. Cryan, professor and chair of the Department of Anatomy and Neuroscience and principal investigator in the APC Microbiome Institute at University College Cork, Ireland, and lead author of this study, the research team has been working on the relationship between stress and the gut microbiome for over 15 years since they discovered that animals that were stressed in early life had an altered microbiome.

“Mice that grow up without microbes have an exaggerated stress response, and certain strains of bacteria can alleviate stress in mice models,” Dr. Cryan explained to Medical News Today.

“While previous research has shown stress and behavior are also linked to our microbiome, it has been unclear until now whether changing diet — and therefore our microbiome — could have a distinct effect on stress levels. This is what our study set out to do,” he said.

MNT also spoke with Lauren Pelehach Sepe, a clinical nutritionist at the Kellman Wellness Center in New York, who further elaborated on the link between stress and the gut microbiome.

“The microbiome is comprised of an entire community of microorganisms that are living within our body. This includes both beneficial bacteria and pathogenic microorganisms, which if not kept in check, can be detrimental to our health.”

“The digestive tract contains its own neural network called the enteric nervous system, which allows for direct communication with the brain or the ‘gut-brain axis.’ The gut-brain axis is essential to our ability to manage stress — when the gut is imbalanced, it impairs our ability to manage stress appropriately.”
— Lauren Pelehach Sepe

Additionally, Sepe mentioned the vagus nerve — known as the 10th cranial nerve — which directly links the gut to the brain.

“In fact, damage to the vagus nerve has been shown to directly impact digestion by slowing the emptying of the stomach. This is also why people often have GI symptoms when under stress,” she continued.

“Although more research is needed, consensus research has shown that there is a link between GI dysfunction and stress-related conditions such as anxiety, depression, and irritable bowel syndrome,” she added.

For this study, participants ate foods high in prebiotic and fermented foods. Researchers call this a “psychobiotic” diet, which is a term Dr. Cryan said his research team coined in 2013 to refer to microbiota-targeted interventions that support mental health. The psychobiotic diet was later the subject of his team’s book, The Psychobiotic Revolution.

For this study, Dr. Cryan and his team enlisted 45 people with relatively low fiber diets, ages 18-59 years, from the Cork area. Researchers directed the participants in the psychobiotic diet group to eat daily:

  • 6-8 servings a day of fruits and vegetables high in prebiotic fibers, including onions, leeks, cabbage, apples, bananas, and oats
  • 5-8 servings a day of grains
  • 2-3 servings a day of fermented foods, including sauerkraut, kefir, or kombucha
  • 3-4 servings per week of legumes

Meanwhile, researchers told participants in the control group to eat according to the food pyramid. And participants in both groups received counseling from a registered dietician.

At the conclusion of the study, researchers found those on the psychobiotic diet reduced their perceived stress — their feelings about how much stress they are currently under. Additionally, scientists found the more a person adhered to the psychobiotic diet, the more they reduced their feelings of stress.

“This was what we anticipated, but we were not sure whether the relatively short time window for testing would be sufficient to induce an effect,” Dr. Cryan said.

After reviewing the study, Sepe said the psychobiotic diet includes foods that are naturally rich in prebiotics — typically fiber-rich foods, which are the best food sources for the beneficial gut microbes — and fermented foods, which are naturally rich in probiotics, the beneficial bacteria that populate our gut.

“These foods help to promote a balanced and healthy gut microbiome, which given the link between gut health and our stress response, may help us to better manage stress,” she said.

Researchers also found sleep quality improved in both the psychobiotic diet and control groups.

Sepe says there are several ways in which diet can impact sleep. For starters, the gut and its microbes are responsible for producing serotonin — the precursor for melatonin, the hormone that regulates circadian rhythm and sleep.

“If we do not produce enough serotonin due to an imbalanced gut microbiome, we will have decreased melatonin production, resulting in impaired sleep patterns,” she explained.

Additionally, Sepe said, the gut microbiome has a role in producing gamma-aminobutyric acid (GABA) — a neurotransmitter that promotes calming and aids with sleep.

“Therefore, by having a diet that supports a healthy gut microbiome, we ensure that we are producing enough of these crucial neurotransmitters,” she detailed.

“[T]here have been studies that have shown that there is a link between gut microbiome composition, diversity, and sleep. Therefore, eating a diet that supports the gut microbiome and ensuring its diversity also impacts healthy sleep patterns.”
— Lauren Pelehach Sepe

For the next steps of this research, Dr. Cryan said he and his research team will try to understand which is the more important component of the diet — fiber or fermented foods.

“Also, these were relatively healthy young participants — it will be important to see how the diet translates to those with stress-related disorders such as anxiety or depression,” he added.

Sepe mentioned diet and nutrition studies are notoriously difficult to run as they rely on participants keeping food diaries and self-reporting, which is prone to errors.

“People generally have difficulty sticking to diets, so it is hard to know for sure if people truly are staying within the parameters of diet,” she explained.

“Although this is not an easy option, rather than leaving people to prepare their own meals, it would be interesting to see a study like this done where maybe some sort of meal delivery service was used, which may allow for a more consistent diet and make it easier for people to comply with it,” she added.