CALIFORNIA — Fermented foods like yoghurt, kimchi, sauerkraut and kombucha have long been dietary staples in many parts of the world. Indeed, for thousands of years, different cultures relied on fermentation to produce bread and cheese, preserve meats and vegetables, and enhance the flavours and textures of many foods.

Now scientists are discovering that fermented foods may have intriguing effects on our gut. Eating these foods may alter the makeup of the trillions of bacteria, viruses and fungi that inhabit our intestinal tracts, collectively known as the gut microbiome.

They may also lead to lower levels of body-wide inflammation, which scientists increasingly link to a range of diseases tied to ageing.

The latest findings come from a study published in the journal Cell that was carried out by researchers at Stanford University. They wanted to see what impact fermented foods might have on the gut and immune system, and how it might compare to eating a relatively healthy diet full of fruits, vegetables, beans, whole grains and other fibre-rich foods.

For the study, the researchers recruited 36 healthy adults and randomly split them into groups. One group was assigned to increase their consumption of fibre-rich plant foods, while a second group was instructed to eat plenty of fermented foods, including yoghurt, sauerkraut, kefir, kombucha and kimchi.

These foods are made by combining milk, vegetables and other raw ingredients with microorganisms like yeast and bacteria. As a result, fermented foods are often teeming with live microorganisms, as well as byproducts of the fermentation process that include various vitamins and lactic and citric acids.

The participants followed the diets for 10 weeks while the researchers tracked markers of inflammation in their blood and looked for changes in their gut microbiomes. By the end of the study, the first group had doubled their fibre intake, from about 22 grams per day to 45 grams daily, which is roughly triple the average American intake.

The second group went from consuming almost no fermented foods to eating about six servings a day. Although six servings might sound like a lot, it does not take much to get there: One cup of yoghurt for breakfast, a 16-ounce bottle of kombucha tea at lunch, and a cup of kimchi at dinner amounts to six daily servings.

After the 10-week period, neither group had significant changes in measures of overall immune health. But the fermented food group showed marked reductions in 19 inflammatory compounds. Among the compounds that showed declines was interleukin-6, an inflammatory protein that tends to be elevated in diseases such as Type Two diabetes and rheumatoid arthritis. The high-fibre group, in contrast, did not show an overall decrease in the same inflammatory compounds.

For people in the fermented foods group, the reductions in inflammatory markers coincided with changes in their guts. They began to harbour a wider and more diverse array of microbes, which is similar to what other recent studies of people who eat a variety of fermented foods have shown.

The new research found that the more fermented foods people ate, the greater the number of microbial species that bloomed in their guts. Yet, surprisingly, just five per cent of the new microbes that were detected in their guts appeared to come directly from the fermented foods that they ate.

“The vast majority came from somewhere else, and we don’t know where,” said Dr Justin Sonnenburg, an author of the new study and a professor of microbiology and immunology at Stanford.

“I think there were either low level microbes below the level of detection that bloomed, or the fermented foods did something that allowed for the rapid recruitment of other microbes into the gut environment.”

The Stanford researchers expected that consuming a high-fibre diet would have a big impact on the makeup of the microbiome. Instead, the high-fibre group tended to show few changes in their microbial diversity.

But when the scientists looked closer, they discovered something striking. People who started out with higher levels of microbial diversity had reductions in inflammation on the high-fibre diet, while those who had the least microbial diversity had slight increases in inflammation when they ate more fibre.

The researchers said they suspect that the people with low microbiome diversity may have lacked the right microbes to digest all the fibre they consumed. One finding that supports this: The high-fibre group had unexpectedly large amounts of carbohydrates in their stool that had not been degraded by their gut microbes.

One possibility is that their guts needed more time to adapt to the high-fibre diet. But ultimately this finding could explain why some people experience bloating and other uncomfortable gastrointestinal issues when they eat a lot of fibre, said Dr Christopher Gardner, another author of the study.

“Maybe the challenges that some people have with fibre is that their microbiomes aren’t prepared for it,” said Gardner, the director of nutrition studies at the Stanford Prevention Research Center.

This article originally appeared in The New York Times.