According to a new study, fermented foods and fiber may help reduce stress.

Foods such as kimchi are great to include in a psychobiotic diet. Credit: Nungning20/ Shutterstock
Foods such as kimchi are great to include in a psychobiotic diet. Credit: Nungning20/ Shutterstock

We're often told that the best ways to deal with stress are to exercise, make time for our favorite activities, or try meditation or mindfulness.

However, according to research published by me and other members of APC Microbiome Ireland, the foods we eat may also be an effective way of dealing with stress. Our most recent study, now published in Molecular Psychiatry, found that eating more fermented foods and fiber on a daily basis had a significant effect on lowering perceived stress levels in just four weeks.

A growing body of research over the last decade has shown that diet can have a significant impact on our mental health. A healthy diet may even lower the risk of developing many common mental illnesses.

The mechanisms underlying the effect of diet on mental health are still unknown. However, one explanation for this connection could be the relationship between our brain and our microbiome (the trillions of bacteria that live in our gut). The gut-brain axis allows the brain and gut to communicate constantly, allowing essential body functions such as digestion and appetite to take place. It also implies that our brain's emotional and cognitive centers are inextricably linked to our gut.

While previous research has linked stress and behavior to our microbiome, it has been unclear whether changing diet (and thus our microbiome) could have a distinct effect on stress levels.

This was the goal of our research. To put this to the test, we gathered 45 healthy people between the ages of 18 and 59 who ate low-fiber diets. More than half of the participants were female. The participants were divided into two groups and randomly assigned a diet to follow for the duration of the four-week study.

Dr. Kirsten Berding, a nutritionist, designed a diet for half of the participants that included more prebiotic and fermented foods. This is referred to as a "psychobiotic" diet because it included foods that have been linked to improved mental health.

At the beginning and halfway through the study, this group received one-on-one education from a dietitian. They were told to aim for 6-8 servings of prebiotic-rich fruits and vegetables per day (such as onions, leeks, cabbage, apples, bananas, and oats), 5-8 servings of grains per day, and 3-4 servings of legumes per week. They were also instructed to consume 2-3 servings of fermented foods per day (such as sauerkraut, kefir and kombucha). Participants on the control diet only received general dietary advice based on the food pyramid for healthy eating.

 Less stress

Surprisingly, those who followed the psychobiotic diet felt less stressed than those who followed the control diet. There was also a link between how strictly participants adhered to the diet and their perceived stress levels, with those who ate more psychobiotic foods during the four-week period reporting the greatest reduction in perceived stress levels.

Interestingly, both groups' sleep quality improved, though those on the psychobiotic diet reported greater improvements. Other research has found that gut microbes are involved in sleep processes, which may explain this link.

The psychobiotic diet only caused minor changes in the composition and function of gut microbes. However, we found that the levels of certain key chemicals produced by these gut microbes changed significantly. Some of these chemicals have been linked to mental health, which may explain why diet participants reported feeling less stressed.

Our findings indicate that certain diets can be used to reduce perceived stress levels. This type of diet may also help to protect mental health in the long run because it targets gut microbes.

While these findings are encouraging, our study has some limitations. First, the sample size is small because the pandemic has limited recruitment. Second, the study's short duration may have limited the changes we observed, and it's unclear how long they would last. As a result, long-term studies will be required.

Third, while participants recorded their daily diet, this method of measurement is prone to error and bias, particularly when estimating food intake. While we did our best to ensure that participants were unaware of their group assignment, they may have been able to guess based on the nutrition advice they were given. This could have influenced their responses at the end of the study. Finally, our study only included people who were already in good health. This means we don't know what effect this diet might have on someone who isn't as healthy.

Nonetheless, our study provides exciting evidence that diet may be an effective way to reduce stress. It will be interesting to see if these findings can be replicated in people with stress-related disorders like anxiety and depression. It also adds to the body of evidence in this field, demonstrating a link between diet, our microbiome, and our mental health.

So, the next time you're feeling particularly stressed, you might want to reconsider what you're going to eat for lunch or dinner. For a few weeks, eating more fiber and fermented foods may help you feel less stressed. 

Journal information: Molecular Psychiatry


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