In this study, to be published in the journal Psychiatry Research in August, US college students were asked about fermented foods in their diet, how worried or neurotic they were in general, and if they suffered social anxiety – an intense fear of humiliation, scrutiny or embarrassment in social situations, which can lead to social withdrawal and isolation.
The fermented foods included yoghurt, kefir, miso soup, sauerkraut, kimchi, fermented soy milk, some dark chocolate, pickles and tempeh. Not all these foods necessarily contain live probiotics – processing tends to kill them off – but the study's authors claim they may still contain the good bacteria.
In addition to fermented foods, the authors also considered the participants' overall diet and amount of exercise.
What the researchers found was that students with high levels of neurotic feelings who also ate more fermented foods reported fewer anxiety symptoms in social situations. Among students with lower background anxiety, the effects were not so pronounced. More exercise was also related to reduced social anxiety.
"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," says Matthew Hilimire, assistant professor of psychology and one of the authors of the paper.
"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," Hilimire says.
More research on humans is in the pipeline.