A diet rich in fermented foods and beverages likely to contain probiotics may help curb social anxiety in young adults, especially those who are highly neurotic, new research suggests.

“While our study cannot definitely determine a causal relationship between fermented food consumption and social anxiety, in combination with the preclinical and clinical studies, our findings suggest that eating more fermented foods can decrease social anxiety,” Matthew Hilimire, PhD, an assistant professor in the Department of Psychology, College of William and Mary, Williamsburg, Virginia, told Medscape Medical News.

“Future studies could test potential applications, such as supplementing drug or cognitive-behavioral therapy with fermented foods,” he said.

The study was published in the August 15 issue of Psychiatry Research and is available online.

Gut-Brain Interaction

The study included 710 students enrolled in introductory courses in psychology at the College of William and Mary. The participants completed questionnaires about fermented food consumption, neuroticism, and social anxiety.

The questionnaire asked about a variety of foods, including yogurt; kefir or food or beverages that contain yogurt; soy milk; miso soup; sauerkraut; dark chocolate; juices that contain microalgae; pickles; tempeh; and kimchi.

“Not all of these foods necessarily had active cultures, but they have the potential to contain probiotics and bioactive peptides,” Dr Hilimire said.

In an interaction model that controlled for demographics, general consumption of healthful foods, and frequency of exercise frequency, the researchers found that exercise frequency, neuroticism, and fermented food consumption significantly and independently predicted social anxiety.

Fermented food consumption also interacted with neuroticism in predicting social anxiety. That is, in students with high degrees of neuroticism, a higher frequency of fermented food consumption correlated with fewer symptoms of social anxiety.

These observations are in line with previous preclinical and clinical trials suggesting that probiotics can have an anxiolytic effect, the researchers say. However, this is the first study to examine the relationship between probiotics and social anxiety, they point out.

“Our study was not able to address the mechanisms because it was a survey of normal eating patterns, social anxiety, and personality. However, previous preclinical studies have suggested potential mechanisms,” Dr Hilimire told Medscape Medical News.

“For example, probiotics reduce the permeability of the gut, so harmful substances don’t leak out. Probiotics also reduce inflammation of the gut. Because anxiety is often accompanied by gastrointestinal symptoms, reducing gut inflammation helps alleviate those symptoms,” he explained.

“Probiotics have also been shown to modify the body’s response to stress, and stress response is highly linked to mental health disorders, such as social anxiety. In addition, consumption of fermented milk has been shown to reduce the brain’s response to negative facial expressions. By reducing the brain’s response to negative social stimuli, social anxiety symptoms might be reduced,” Dr Hilimire noted.

Public Health Implications

Commenting on the findings for Medscape Medical News, Bonnie J. Kaplan, PhD, who studies nutrition and mood at the University of Calgary, in Alberta, Canada, said research on the gut microbiome is expanding enormously, as is research on genetic influences on mental disorders.

“This study is interesting in how it ties together several relevant threads of personality, food intake, and exercise -  specifically, personality traits presumed to reflect genetic predisposition, such as neuroticism, a measure of social phobia and anxiety, reported exercise levels, and dietary intake of fermented foods as well as fruits and vegetables.”

“Also of interest is the fact that the information was not collected from a clinical sample of people with diagnosed anxiety disorders…participants were first-year psychology students in an American liberal arts university. This means the results have implications for broad, population health,” said Dr Kaplan.

“The authors interpret their results as indirect evidence that probiotics (assumed to be in the fermented foods) are combating anxiety. This final point is an inference that will need further research,” she added.

As reported previously by Medscape Medical News, Dr Kaplan’s own research has shown a strong link between higher levels of nutrient intake and better mental health -  adding to the growing body of evidence demonstrating the critical role of diet in mood disorders.

The authors and Dr Kaplan report no relevant financial relationships.

Psychiatry Res. 2015;228:203-208. Abstract