A diet high in fermented foods increases microbiome diversity, lowers inflammation, and improves immune response, according to researchers at Stanford University’s School of Medicine.The groundbreaking results were published in the journal Cell.
In the clinical trial, healthy individuals were fed for 10 weeks, a diet either high in fermented foods and beverages or high in fiber. The fermented diet — which included yogurt, kefir, cottage cheese, kimchi, kombucha, fermented veggies and fermented veggie broth — led to an increase in overall microbial diversity, with stronger effects from larger servings.
“This is a stunning finding,” says Justin Sonnenburg, PhD, an associate professor of microbiology and immunology at Stanford. “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.”
Researchers were particularly pleased to see participants in the fermented foods diet showed less activation in four types of immune cells. There was a decrease in the levels of 19 inflammatory proteins, including interleukin 6, which is linked to rheumatoid arthritis, Type 2 diabetes and chronic stress.
“Microbiota-targeted diets can change immune status, providing a promising avenue for decreasing inflammation in healthy adults,” says Christopher Gardner, PhD, 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.”
Microbiota Stability vs. Diversity
Continues a press release from Stanford Medicine News Center: By contrast, none of the 19 inflammatory proteins decreased in participants assigned to a high-fiber diet rich in legumes, seeds, whole grains, nuts, vegetables and fruits. On average, the diversity of their gut microbes also remained stable.
“We expected high fiber to have a more universally beneficial effect and increase microbiota diversity,” said Erica Sonnenburg, PhD, a senior research scientist at Stanford 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.”
Justin and Erica Sonnenburg and Christopher Gardner are co-authors of the study. The lead authors are Hannah Wastyk, a PhD student in bioengineering, and former postdoctoral scholar Gabriela Fragiadakis, PhD, now an assistant professor of medicine at UC-San Francisco.
A wide body of evidence has demonstrated that diet shapes the gut microbiome which, in turn, can affect the immune system and overall health. According to Gardner, low microbiome diversity has been linked to obesity and diabetes.
“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 researchers focused on fiber and fermented foods due to previous reports of their potential health benefits. High-fiber diets have been associated with lower rates of mortality. Fermented foods are thought to help with weight maintenance and may decrease the risk of diabetes, cancer and cardiovascular disease.
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.
The findings paint a nuanced picture of the influence of diet on gut microbes and immune status. Those who increased their consumption of fermented foods showed effects consistent with prior research showing that short-term changes in diet can rapidly alter the gut microbiome. The limited changes in the microbiome for the high-fiber group dovetailed with previous reports of the resilience of the human microbiome over short time periods.
Designing a suite of dietary and microbial strategies
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 research suggesting that the microbiome of a person 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.”
In addition to exploring these possibilities, the researchers plan to conduct studies in mice to investigate the molecular mechanisms by which diets alter the microbiome and reduce inflammatory proteins. They also aim to test whether high-fiber and fermented foods synergize to influence the microbiome and immune system of humans. Another goal is to examine whether the consumption of fermented foods decreases inflammation or improves other health markers in patients with immunological and metabolic diseases, in pregnant women, or in 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.
Other Stanford co-authors are Dalia Perelman, health educator; former graduate students Dylan Dahan, PhD, and Carlos Gonzalez, PhD; graduate student Bryan Merrill; former research assistant Madeline Topf; postdoctoral scholars William Van Treuren, PhD, and Shuo Han, PhD; Jennifer Robinson, PhD, administrative director of the Community Health and Prevention Research Master’s Program and program manager of the Nutrition Studies Group; and Joshua Elias, PhD.