The different effects of fermented foods and fiber on the immune system
A diet rich in fermented foods improves the diversity of intestinal microbes and decreases the molecular signs of inflammation, according to researchers at Stanford School of Medicine.
In a clinical study, 36 healthy adults were randomly assigned to two groups that followed different diets over ten weeks: one that included fermented foods and one that was high in fiber. The two diets led to different effects on the intestinal microbiota and on the immune system. Here are the most important conclusions.
What happens in your body when you eat a diet with fermented foods?
Consumption of foods such as yogurt, kefir, fermented cottage cheese, kimchi and other fermented vegetables, vegetable drinks with brine or kombucha tea, leads to an increase in general microbial diversity, with stronger effects from larger portions. “This is an amazing finding,” said Justin Sonnenburg, an associate professor of microbiology and immunology. “It’s one of the first examples of how a simple dietary change can reshape a microbiota in a group of healthy adults.”
In addition, four types of immune cells were less active in the group of those who ate fermented foods. Also, the levels of 19 inflammatory proteins measured in blood samples have decreased, and one of these proteins, interleukin 6, is associated with conditions such as rheumatoid arthritis, type 2 diabetes or chronic stress.
“Microbiotic diets can change the immune system, providing a promising way to reduce inflammation in healthy adults,” said Christopher Gardner, a professor of medicine at Stanford University and director of nutrition studies at the Stanford Prevention Research Center. This finding was present among all study participants who were assigned to the group with superior fermented foods.
Increased fiber intake over a short period of time is insufficient to develop microbiota diversity
In the study participants with a high-fiber diet, such as seeds, whole grains, nuts, vegetables and fruits, the diversity of the microbiota did not change and none of the 19 inflammatory proteins decreased.
“We expected a high level of fiber to have a universal beneficial effect and increase the diversity of the microbiota,” said Erica Sonnenburg, a senior researcher in basic life sciences, microbiology and immunology.
The study was published online in July this year on the Cell platform, and Justin and Erica Sonnenburg and Christopher Gardner are senior co-authors. The lead authors are Hannah Wastyk, a doctoral student in bioengineering, and former postdoctoral researcher Gabriela Fragiadakis, now an assistant professor of medicine at the University of California, San Francisco.
A wealth of evidence has shown that diet shapes the gut microbiome, which can affect the immune system and overall health. According to Gardner, the low diversity of microbiomes has been associated with obesity and diabetes.
While high-fiber diets have been associated with lower mortality rates, eating fermented foods can help maintain weight and reduce the risk of diabetes, cancer and cardiovascular disease.
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