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The gut microbiota is composed of the community of bacteria, archaea, fungi, and viruses that live in the human intestine. Dietary components influence the composition and activity of the microbiota. For example, foods high in dietary fiber, such as whole grains and beans, and fermented foods, such as yogurt and sauerkraut, support an abundant and diverse gut microbiota, which is associated with lower disease risk. Authors of a report released this week investigated the effects of high-fiber and fermented foods on the gut microbiota and immune system.

The authors recruited 36 healthy adult participants (average age, 52 years) who consumed little dietary fiber (fewer than 20 grams of fiber per day) and only one serving of fermented foods or less per day. They instructed half of the participants to add 20 grams or more of fiber per day to their baseline consumption. They instructed the other half of participants to consume six servings or more of fermented foods per day. Participants in both groups consumed their assigned diets for 10 weeks and recorded their food and beverage intake to assess adherence to study instructions. Participants also provided blood samples for the assessment of inflammation and fecal samples for the characterization of the gut microbiome at numerous time points throughout the study.

A high-fiber diet did not reduce inflammation, but did alter the composition of the microbiota, increasing the abundance of bacteria known to metabolize dietary fibers, such as the genus Lachnospira. Higher fiber consumption also promoted greater secretion of enzymes associated with fiber metabolism and increased abundance of fiber metabolites, such as short chain fatty acids. A high-fermented food diet steadily increased microbiota diversity over time and decreased multiple markers of inflammation, including interleukin (IL)-6, IL-10, and IL-12b, among others.

These results suggest that probiotics from fermented foods increase microbiota diversity and decrease inflammation. The authors noted that the lack of immunological response in participants consuming the high fiber diet may have been due to the short duration of the intervention.

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