People who consumed more fermented products over a 10-week study period also had an increase in microbiome diversity and a decrease in immune cell activation. “This is a stunning finding,” said coauthor Justin Sonnenburg, PhD, associate professor of microbiology and immunology at Stanford University School in Palo Alto, California. “These results are one of the first examples of how a simple change in diet can reproducibly remodel the microbiota in a group of healthy adults.”
What Is the Microbiome, And How Does It Impact Our Health?
The gastrointestinal tract is full of bacteria, fungi, and even viruses. The activity and composition of these microorganisms are collectively known as the gut microbiota or microbiome. Probiotics, which are found in fermented foods such as cultured milk and yogurt, tempeh, miso, sauerkraut, and brine drinks, are live microorganisms that experts believe can help improve the diversity of the microbiome, according to the National Institutes of Health. Fiber rich foods, on the other hand, contain prebiotics. These indigestible fibers are found in grains, fruits and vegetables, and also help feed the good bacteria in your gut, according to the UMass Center for Applied Nutrition. So why is diversity in our gut a good thing? For starters, less diversity is associated with chronic inflammatory conditions like obesity and diabetes. When the microbiome is less diverse, it could lead to certain bacteria outgrowing others and potentially secreting enzymes that lead to inflammation and other negative effects, explains C. Scott Mahan, MD, chief of medicine at Charles George VA Medical Center in Asheville, North Carolina, and coauthor of the textbook Clinical Microbiology Made Ridiculously Simple. Dr. Mahan was not involved in the study. “Even our own immune system could react to this imbalance by immune cells secreting enzymes which cause inflammation,” says Mahan.
How the Study Was Conducted
Investigators set out to determine if eating a diet designed to improve gut diversity — either one rich in fiber or one rich in fermentation — could have potential benefits for lowering inflammation and battling chronic inflammatory diseases. In the study, published in July 2021 in the journal Cell, healthy adults were divided into two groups, with 21 people eating high-fiber foods such as fruits, whole grains, legumes, vegetables, nuts, and seeds, and 18 people consuming fermented foods. Stool samples were collected from the subjects during a three-week pretrial period, during the 10 weeks of following the assigned diet, and then for a four-week period after the study, when participants went back to eating whatever they wanted. Blood samples were also taken to measure inflammation and immune function. In addition to increasing the diversity of the gut microbiome, people who ate fermented foods showed less activation for four types of immune cells and the levels of several inflammatory proteins, including interleukin 6, also decreased. Interleukin 6 is elevated in many chronic inflammatory disorders including rheumatoid arthritis (RA), lupus, ankylosing spondylitis (AS) and inflammatory bowel disease (IBD), according to Mayo Clinic Laboratories. The findings were strengthened by a dose dependent relationship- the larger the servings of fermented foods, the greater the effect. These findings should prompt further investigation, says Mahan. “At the very least this suggests that highly fermented foods should be part of a balanced diet,” he adds.
Diversity of Microbiome Not Observed in High Fiber Group
Somewhat surprisingly, the participants who focused on eating fruits, vegetables, and plant-based sources of protein such as whole grains and nuts, did not have an increase in their microbiota diversity. It is possible that the short study wasn’t long enough to show the benefits of fiber in the microbiota, said Erica Sonnenburg, PhD, coauthor and senior scientist at Stanford. It’s also possible that people who have been consuming a typical American diet don’t have the type of bacteria that can break down fiber to unleash the full benefits, the authors speculate. If further research confirms that theory, the right kind of fiber-consuming microbes may need to be deliberately added to the diet in order to fiber to improve diversity.
