A diet rich in fermented foods enhances the diversity of gut microbes and decreases molecular signs of inflammation, according to researchers at the Stanford School of Medicine. These researchers conducted a clinical trial with 36 healthy adults. The participants were randomly assigned to a 10-week diet that included either fermented or high-fiber foods. Each type of diet had different effects on the gut microbiome and the immune system.
The study showed that consuming fermented foods like kimchi, kefir, yogurt, vegetable brine drinks, fermented vegetables, and kombucha tea helped increase microbial diversity. Consuming larger portions of fermented foods resulted in stronger effects.
“This is a stunning finding,” said Justin Sonnenburg, Ph.D., an associate professor of microbiology and immunology. “It provides one of the first examples of how a simple change in diet can reproducibly remodel the microbiota across a cohort of healthy adults.”
In addition, certain immune cells showed less activation in the fermented foods group. The levels of 19 inflammatory proteins in the blood also decreased. One of the proteins interleukin 6, has been associated with conditions like rheumatoid arthritis, chronic stress, and Type 2 diabetes.
“Microbiota-targeted diets can change immune status, providing a promising avenue for decreasing inflammation in healthy adults,” said Christopher Gardner, Ph.D., the Rehnborg Farquhar Professor and director of nutrition studies at the Stanford Prevention Research Center. “This finding was consistent across all participants in the study who were assigned to the higher fermented food group.”
Fiber-rich diet produced stable microbe diversity
However, the participants in the high-fiber diet study showed different results. None of the 19 inflammatory proteins decreased for those people, whose diets included fruit and vegetables, whole grains, seeds, legumes, and nuts. The diversity of their microbiome remained stable.
“We expected high fiber to have a more universally beneficial effect and increase microbiota diversity,” said Erica Sonnenburg, Ph.D., a senior research scientist in basic life sciences, microbiology, and immunology. “The data suggest that increased fiber intake alone over a short time period is insufficient to increase microbiota diversity.”
The study was published in Cell in July. Justin and Erica Sonnenburg and Christopher Gardner were co-senior authors. The lead authors were Hannah Wastyk, a Ph.D. student in bioengineering, and former postdoctoral scholar Gabriela Fragiadakis, Ph.D., who is now an assistant professor of medicine at UC-San Francisco.
A growing body of evidence shows that diet has an important impact on the gut microbiome, which in turn affects the immune system and overall well-being. In addition, low microbiome diversity has been linked to diabetes and obesity.
“We wanted to conduct a proof-of-concept study that could test whether microbiota-targeted food could be an avenue for combatting the overwhelming rise in chronic inflammatory diseases,” Gardner said.
The scientists chose fermented foods and high-fiber foods because of previous studies showing their health benefits. Consuming fermented foods may help with maintaining a healthier weight and decrease the risk of cancer, diabetes, and cardiovascular disease. High-fiber diets have been linked with lower rates of mortality.
The researchers analyzed blood and stool samples collected during a three-week pre-trial period, the 10 weeks of the diet, and a four-week period after the diet when the participants ate as they chose.
Their results add insight into how our diets can alter gut microbes and the immune system. Participants who ate higher levels of fermented foods showed results that supported previous research. Their diets influenced their microbiome diversity and inflammatory markers. The results happened quickly. The participants in the high-fiber diet group support findings that the diet has a positive impact on the general resilience of the microbiome over short time periods.
The results also showed that greater fiber intake led to more carbohydrates in stool samples, pointing to incomplete fiber degradation by gut microbes. These findings are consistent with other research suggesting that the microbiome of people living in the industrialized world is depleted of fiber-degrading microbes.
“It is possible that a longer intervention would have allowed for the microbiota to adequately adapt to the increase in fiber consumption,” Erica Sonnenburg said. “Alternatively, the deliberate introduction of fiber-consuming microbes may be required to increase the microbiota’s capacity to break down the carbohydrates.”
The researchers plan to continue investigating these findings by conducting more studies in mice. Their objective is to look into the molecular mechanisms by which diets alter the microbiome and reduce inflammatory proteins. In addition, they will investigate whether fermented and high-fiber foods can work in synergy to improve the microbiome and immune systems in humans. Another goal is to examine whether the consumption of fermented food decreases inflammation or improves other health markers in patients with immunological and metabolic diseases, and in pregnant women and older individuals.
“There are many more ways to target the microbiome with food and supplements, and we hope to continue to investigate how different diets, probiotics, and prebiotics impact the microbiome and health in different groups,” Justin Sonnenburg said.