Fiber foods

A microbiome study of a fermented diet versus a high-fiber diet shows surprising results

By studying the relationship between diet, gut bacteria and systemic inflammation, a team of Stanford University researchers found that just weeks after eating a diet high in fermented foods can lead to improvements in diversity. microbiome and reductions in inflammatory biomarkers.

The new research pitted a high-fiber diet against a diet high in fermented foods. Thirty-six healthy adults were recruited and randomly assigned to one of two diets for 10 weeks.

“We wanted to conduct a proof-of-concept study that could test whether microbiota-targeted foods could be a way to combat the overwhelming rise in chronic inflammatory diseases,” says Christopher Gardner, co-lead author of the new study.

Blood and stool samples were taken before, during and after the dietary intervention. During the trial, researchers saw levels of 19 inflammatory proteins drop in the fermented food cohort. This was accompanied by increased microbial diversity in the gut and reduced activity in four types of immune cells.

Perhaps more importantly, these changes were not detected in the group instructed to follow a high-fiber diet. Erica Sonnenburg, another co-lead author of the study, says this discordance between the two cohorts was unexpected.

“We expected that high fiber content would have a more universal beneficial effect and increase microbiota diversity,” she says. “The data suggest that increasing fiber intake over a short period of time is insufficient to increase microbiota diversity.”

One hypothesis raised in the study to explain the different responses to the two diets is that fiber-induced increases in microbiota diversity may take longer to manifest than changes induced by fermented foods. Several biomarker changes were noted in the high-fiber diet cohort, including altered short-chain fatty acid production and increased microbial protein density in the stool. The researchers note that these are indications that high-fiber diets may reshape gut microbial populations, but potentially at a slower rate than fermented foods.

“It’s possible that a longer intervention would have allowed the microbiota to adequately adapt to the increased fiber intake,” Sonnenburg notes. “Alternatively, the deliberate introduction of fiber-consuming microbes may be necessary to increase the microbiota’s ability to break down carbohydrates.”

Perhaps the greatest benefit of this new study is the rapid immune system and microbiome changes induced by the fermented diet and the consistency of responses across the cohort. Justin Sonnenburg, another researcher working on the project, called the results an “astonishing” demonstration of how a small dietary change in healthy adults can influence microbial diversity and resultant immune activity.

The next step for researchers will be to move to animal studies and explore the specific mechanisms involved in these diet-induced changes. Additionally, researchers are also curious whether a combination high-fiber and fermented diet improves these responses.

“There are many other ways to target the microbiome with foods and supplements, and we hope to continue to study the impact of different diets, probiotics and prebiotics on the microbiome and health in different groups,” says Justin Sonnenburg.

The new study has been published in the journal Cell.

Source: Stanford Medicine