The researchers found that young adults who eat more fermented foods have fewer social anxiety symptoms, with the effect being greatest among those at genetic risk for social anxiety disorder as measured by neuroticism.
Previous studies had looked at the connection between probiotics and anxiety or depression in animal models, but this was the first naturalistic study in humans to look at the connection between non-manipulated food intake, personality and social anxiety, Hilimire, assistant professor of psychology, said:
“It is likely that the probiotics in the fermented foods are favorably changing the environment in the gut, and changes in the gut in turn influence social anxiety. I think that it is absolutely fascinating that the microorganisms in your gut can influence your mind.
These studies with animal models showed that if you give them certain kinds of bacteria, which we call probiotics – the beneficial microorganisms that help our health, like lactobacilli – these animals tend to be less depressed or less anxious.”
Based on those findings, researchers have been able to look at the different mechanisms at play, including decreased gut permeability and inflammation and increased GABA, a neurotransmitter that’s mimicked by anti-anxiety medications like benzodiazepines.
“Giving these animals these probiotics increased GABA, so it’s almost like giving them these drugs but it’s their own bodies producing GABA,” he said. “So your own body is increasing this neurotransmitter that reduces anxiety.”
In addition to the animal studies, a few human trials have been conducted, wherein researchers have isolated probiotics and given them to people, resulting in a reduction of depression and anxiety symptoms. But no studies had specifically looked at social anxiety.
“Given that background, we were interested in doing a naturalistic study,” said Hilimire. “So, we didn’t actually give people probiotics, we just asked them in their day-to-day life how much fermented foods they were eating.”
The researchers designed a questionnaire to be included in a mass testing tool administered in the university’s Introduction to Psychology courses.
“It was an ideal situation to get a good cross-section of the students at William & Mary because many students take Intro to Psych,” said Forestell, associate professor of psychology. “They were not selected based on their social anxiety or the types of foods that they ate. They were pretty representative of the students at William & Mary.”
“Neuroticism is more of a stable personality trait, so it should tap into the underlying way that you interact with the world,” said Hilimire. “And so it’s a continuum where one end is emotional stability and the other end is neuroticism.”
Since the mass testing tool already included ways to measure social anxiety and neuroticism, the researchers added a questionnaire about eating habits, asking the students about their consumption of fermented foods over the previous 30 days, foods such as:
fermented soy milk
The questionnaire also asked about exercise frequency and the average consumption of fruits and vegetables so that the researchers could control for healthy habits outside of fermented food intake, said Hilimire.
“The main finding was that individuals who had consumed more fermented foods had reduced social anxiety but that was qualified by an interaction by neuroticism. What that means is that that relationship was strongest amongst people that were high in neuroticism,” Hilimire said.
“The people that benefitted the most from fermented foods were high in neuroticism. And the secondary finding was that more exercise was related to reduced social anxiety, as well.”
The researchers will also soon create an experimental version of the study, looking specifically at social anxiety and using fermented foods as opposed to probiotic supplements, which lack the bioactive proteins that can also affect the brain.
“If we use a naturally fermented food – we give people yogurt instead of isolated probiotics – it will be among the first experimental studies that use these fermented foods, so they’ll get the benefits of the probiotics but also the peptides, as well,” said Hilimire.
Without that experimental phase, the researches can’t make a causative connection between eating fermented foods and reduced social anxiety.
“However, if we rely on the animal models that have come before us and the human experimental work that has come before us in other anxiety and depression studies, it does seem that there is a causative mechanism,” said Hilimire.
“Assuming similar findings in the experimental follow-up, what it would suggest is that you could augment more traditional therapies (like medications, psychotherapy or a combination of the two) with fermented foods – dietary changes – and exercise, as well.”
As long as a person is healthy enough to exercise, there shouldn’t be any negative consequences of those supplements, Hilimire added.
“So, a young, healthy person should be able to take these without any negative consequences, which can’t be said for things like benzodiazepines, which can be addictive and have potential for overdose.”
The mind-gut connection is still a relatively new concept in the field of psychology. Many of the people currently doing the work are microbiologists or people trained in naturopathic medicine, but studies like this one may be on the forefront of changing conventional wisdom on the topic.
“I think there is some skepticism that there can be such a profound influence, but the data is quite substantial now,” said Hilimire. “I think people would be accepting if they looked at the data, but the connection between the mind and gut is not something you typically think about as a psychologist.”
“Animal models and clinical trials in humans suggest that probiotics can have an anxiolytic effect. However, no studies have examined the relationship between probiotics and social anxiety. Here we employ a cross-sectional approach to determine whether consumption of fermented foods likely to contain probiotics interacts with neuroticism to predict social anxiety symptoms. A sample of young adults (N=710, 445 female) completed self-report measures of fermented food consumption, neuroticism, and social anxiety. An interaction model, controlling for demographics, general consumption of healthful foods, and exercise frequency, showed that exercise frequency, neuroticism, and fermented food consumption significantly and independently predicted social anxiety.
Moreover, fermented food consumption also interacted with neuroticism in predicting social anxiety. Specifically, for those high in neuroticism, higher frequency of fermented food consumption was associated with fewer symptoms of social anxiety. Taken together with previous studies, the results suggest that fermented foods that contain probiotics may have a protective effect against social anxiety symptoms for those at higher genetic risk, as indexed by trait neuroticism. While additional research is necessary to determine the direction of causality, these results suggest that consumption of fermented foods that contain probiotics may serve as a low-risk intervention for reducing social anxiety.”