How fermented foods alter the microbiome and improve health

Fermented foods like yogurt, 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 flavors 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 aging.

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 fiber-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 fiber-rich plant foods, while a second group was instructed to eat plenty of fermented foods, including yogurt, 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 fiber 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 yogurt 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 2 diabetes and rheumatoid arthritis. The high-fiber 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 harbor 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 5 percent of the new microbes that were detected in their guts appeared to come directly from the fermented foods that they ate.

New York Times

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