Fermented foods stimulate microbiome diversity and enhance immune responses

A recent study published in the journal Cell suggests that within a few weeks a diet rich in fermented foods improves the diversity of the gut microbiome as well as the immune responses.

Gut bacteria are so important to our health that some consider them to be a full body. They digest our food, neutralize some of the toxic byproducts of the digestive process and protect us from certain diseases. A low microbial diversity in our intestines has in particular been linked to obesity and diabetes. As part of recent work, researchers at Stanford University (United States) investigated how food could or could not influence the composition of this microbiome.

We wanted to conduct a proof-of-concept study that could test whether foods targeted to the microbiota could be a way to fight the overwhelming increase in chronic inflammatory disease.“Says Dr. Christopher Gardner, Director of Nutrition Studies at the Stanford Prevention Research Center.

For this research, the team focused on two diets, one high in fiber, the other high in fermented foods. Note that previous studies have already reported the health benefits of these.

In a clinical trial, researchers recruited thirty-six healthy adults that were randomly assigned to one of the two regimes for ten weeks. Blood and stool tests were then performed. The researchers analyzed blood and stool samples during a three-week pre-test period, during the ten-week study period, and also during a four-week period following each diet.

These two approaches then had different effects on the gut microbiome and the immune system.

Microbial diversity and immune responses

On the one hand, the consumption of fermented foods, such as yogurt, kefir, fermented cottage cheese, kimchi, and other fermented vegetables has resulted in a increase in overall microbial diversity. Also, the larger the servings, the better the effects.

It’s an amazing find“Said Justin Sonnenburg, Associate Professor of Microbiology and Immunology and co-author of this work. “This provides one of the first examples of how a simple change in diet can reproducibly reshape the microbiota in a cohort of healthy adults.“.

In addition, four types of immune cells showed less activation in the group subjected to the fermented diet. Finally, the levels of nineteen inflammatory proteins measured in blood samples have also decreased. One of them, interleukin 6, has already been linked to conditions such as rheumatoid arthritis, type 2 diabetes and chronic stress, the researchers say.

Thus, for Dr. Gardner, diets targeted to the microbiota can therefore “Alter immune status, offering promising pathway to reduce inflammation in healthy adults“.

Kimchi, a traditional Korean dish made with peppers and lacto-fermented vegetables (soaked in brine). Credit: Jeremy Keith

In the short term, no changes to the high fiber diet

Conversely, none of these 19 inflammatory proteins decreased in participants of the high-fiber diet (legumes, seeds, whole grains, nuts, vegetables and fruits). On average, the diversity of their gut microbes also remained stable.

We expected that the high fiber content would have a more universal beneficial effect and increase the diversity of the microbiota.“Said Erica Sonnenburg, co-author of the study. “The data suggest that increasing fiber intake alone over a short period of time is insufficient to increase microbiota diversity ”.

Note that this study was conducted over a very short period of time. Also, a longer exposure to these fibers could allow the microbiota to adapt adequately to the increase in fiber consumption.. Alternatively, notes the researcher, the deliberate introduction of fiber-consuming microbes may be necessary to increase the microbiota’s ability to break them down.“.

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