Greater diversity in the gut microbiome is generally considered a good thing. Studies have linked it to lower rates of obesity, type 2 diabetes, metabolic disorders, and other diseases. People who live in developed nations tend to have less microbial diversity in their stomachs than people who live in more traditional, non-industrialized societies. Some scientists speculate that modern lifestyle factors like Diets high in processed foods, chronic stress, and physical inactivity can suppress the growth of potentially beneficial gut microbes. Others argue that the correlation between diverse microbiomes and good health is exaggerated and that the low level of microbiome diversity typically seen in people in developed countries might be appropriately adapted to a modern world.
One topic that there is little disagreement about among nutritionists is the benefits of a high-fiber diet. In large studies, people who consume more fruits, vegetables, nuts, and other high-fiber foods tend to have lower death rates and fewer chronic illnesses. Fiber is considered good for gut health: microbes in the gut feed on fiber and use it to produce useful by-products like short chain fatty acids that can reduce inflammation. Some studies also suggest that consuming lots of fiber promotes a diverse microbiome.
The Stanford researchers expected that a high-fiber diet would have a huge impact on the composition of the microbiome. Instead, the high-fiber group tended to show few changes in their microbial diversity. But when the scientists took a closer look, they discovered something conspicuous. People who started with higher microbial diversity showed a decrease in inflammation on the high-fiber diet, while those with the lowest microbial diversity had a slight increase in inflammation when they consumed more fiber.
The researchers said they suspect that people with low microbiome diversity may lack the right microbes to digest all of the fiber they consume. One finding that supports this: The high-fiber group had unexpectedly large amounts of carbohydrates in their stool that were not broken down by their gut microbes. One possibility is that her bowels took more time to adjust to the high-fiber diet. But ultimately, this finding could explain why some people experience gas and other uncomfortable gastrointestinal problems when they eat a lot of fiber, said Christopher Gardner, another author on the study.
“Perhaps the challenge some people have with fiber is that their microbiome isn’t prepared for it,” said Dr. Gardner, the director of nutritional studies at the Stanford Prevention Research Center.
One question the researchers want to answer in the future is what would happen if people consumed more fermented foods and more fiber at the same time. Would that increase the variety of microbes in your gut and improve your ability to digest more fiber? Would the two have a synergistic effect on inflammation?
Suzanne Devkota, director of microbiome research at Cedars-Sinai Medical Center in Los Angeles, who wasn’t involved in the new study, said fermented foods had long been believed to have health benefits, but the new research was some of the first provides “hard evidence” that it can affect the gut and inflammation. “We have always been a little reluctant to comment on whether fermented foods are beneficial, especially from an inflammatory point of view, because there really was no data behind it,” she said.