The results of a clinical study conducted by American scientists have shown that fermented foods increase the diversity of intestinal microbes, reduce inflammation and increase immunity. The results of the study are published in the journal Cell.

Scientists from the Stanford School of Medicine decided to test how fermented foods and foods with high fiber content affect the intestinal microbiome and the immune system. To do this, they conducted a clinical study in which 36 healthy adults participated.

The volunteers were randomly divided into two groups. For ten weeks, one group ate fermented foods, including yogurt, kefir, cottage cheese, fermented vegetables, kimchi, pickled drinks, and kombucha, and the other group ate high—fiber foods — legumes, seeds, whole grains, nuts, vegetables, and fruits.

During the three weeks before the start of the study, the entire period of the experiment, and four weeks after it, blood and stool samples were taken from the participants. As a result, it turned out that people from the first group who ate fermented foods increased their overall microbial diversity and decreased the level of inflammatory proteins, including interleukin 6, which is associated with conditions such as rheumatoid arthritis, type 2 diabetes, and chronic stress. In the volunteers from the second group, the composition of the intestinal microbiota remained stable and none of the 19 inflammatory proteins decreased.

“This is an amazing discovery, one of the first examples of how a simple change in diet can replenish the microbiota,” said the head of the study, Dr. Justin Sonnenburg, associate professor of microbiology and immunology, in a press release from the Stanford School of Medicine.

“We expected that a high fiber content would have a more universal positive effect and lead to an increase in the diversity of the microbiota,” continues Erica Sonnenburg, another author of the article, a senior researcher in the field of basic life sciences, microbiology, and immunology at the Stanford School of Medicine. “But the data show that just consuming fiber for a short period of time is not enough to increase microbial diversity.”

It is known that the composition of food largely determines the composition of the intestinal microbiome, which, in turn, affects the immune system and overall health. In particular, the low diversity of intestinal microbes determines the predisposition to diabetes and obesity.

“Microbiota-targeted diets can change the immune status, providing promising opportunities to reduce inflammation in healthy adults,” said Professor Christopher Gardner, director of nutrition research at the Stanford Prevention Center, who participated in the study. — We wanted to test whether food aimed at the microbiota can become a means of combating chronic inflammatory diseases.”

The authors believe that a diet based on fermented foods helps to maintain a normal weight, reduces the risk of diabetes, cancer, and cardiovascular diseases.

The results also showed that a higher intake of fiber leads to an increase in the number of carbohydrates in the stool samples, which indicates incomplete decomposition of fiber by intestinal microbes. These results are consistent with other studies suggesting that the microbiome of people living in the industrialized world is depleted of microbes that destroy fiber.