What is already known on this topic
Mounting evidence suggests that diet influences the gut microbiota composition and function, which in turn can affect the immune system and overall health. But it’s unclear whether dietary changes that leverage microbiota-host interactions can improve health.

What this research adds
Researchers enrolled 36 healthy adults in a clinical trial and randomly assigned them to one of two groups: one group followed a 10-week diet that included high-fiber foods, whereas the other followed a 10-week diet that included fermented foods such as yogurt, kombucha tea, kimchi and other fermented vegetables. People who ate fermented foods showed a higher gut microbiota diversity and lower signs of inflammation than did those on a diet rich in high-fiber foods.

Conclusions
The findings suggest that fermented foods can help countering the decreased microbiota diversity and heightened inflammation that characterize industrialized populations.

 

Mounting evidence suggests that diet influences the gut microbiota composition and function, which in turn can affect the immune system and overall health. Now, researchers have found that a diet rich in fermented food such as yogurt, kombucha tea, kimchi and other fermented vegetables can boost the diversity of gut microbes and decrease molecular signs of inflammation.

The results, published in Cell, suggest that fermented foods can help countering the decreased microbiota diversity and heightened inflammation that characterize industrialized populations.

“This is a stunning finding,” says study senior co-author Justin Sonnenburg at Stanford School of Medicine. “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.”

So far, it’s been unclear whether dietary changes that leverage microbiota-host interactions can improve health. Sonnenburg and his colleagues set out to determine how two dietary interventions — high-fiber foods and fermented foods — influence the human microbiota and immune system. High-fiber diets have been linked to lower rates of mortality, and fermented foods diets may decrease the risk of conditions such as diabetes and cardiovascular disease, the researchers say.

Diet effect

The team enrolled 36 healthy adults in a clinical trial and randomly assigned them to one of two groups: one group followed a 10-week diet that included fermented foods, whereas the other followed a 10-week diet that included high-fiber foods such as legumes, whole grains, and nuts. The team collected the participants’ blood and stool samples before, during, and after the dietary intervention.

People who ate fermented foods showed a higher gut microbiota diversity than did those on a diet rich in high-fiber foods. Low microbiota diversity has been linked to obesity and diabetes. 

Trial participants who consumed fermented foods showed decreased activation of four types of immune cells and lower levels of 19 inflammatory proteins in their blood. One of these proteins has been linked to conditions including diabetes and chronic stress. None of these inflammatory proteins decreased in people who consumed a high-fiber diet, the researchers found.

Different responses

In people on a high-fiber diet, the researchers observed altered levels of short-chain fatty acids and increased carbohydrates in stool samples. This suggests that microbes in the gut of these individuals could not completely degrade fiber, which supports the idea that the microbiota of industrialized populations has low levels of fiber-degrading microbes.

The different responses to the two diets could be due to the fact that changes in microbiota diversity induced by fiber take longer to manifest than those induced by fermented food, the researchers say. “It is possible that a longer intervention would have allowed for the microbiota to adequately adapt to the increase in fiber consumption,” says study senior co-author Erica Sonnenburg. “Alternatively, the deliberate introduction of fiber-consuming microbes may be required to increase the microbiota’s capacity to break down the carbohydrates.”

The team now plans to investigate the molecular mechanisms by which different diets alter the microbiota, and whether consuming fermented food reduces inflammation in people with immune and metabolic diseases. “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,” Sonnenburg says.

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Giorgia Guglielmi is a freelance science writer based in Cambridge, Massachusetts. She received a PhD in Biology from the European Molecular Biology Laboratory and a Master’s in Science Writing from the Massachusetts Institute of Technology.