The gut microbiome is the community of microorganisms that lives in the digestive tract.
Diet is one of the factors that can influence this complex ecosystem. Fermented foods are particularly interesting because microorganisms have already transformed the food before we eat it.
But different fermented foods may interact with the gut microbiome in different ways.
Some fermented foods contain live microorganisms
Natural yogurt is produced using bacterial cultures and may contain live microorganisms when consumed.
Kefir is produced through a different fermentation process, traditionally involving a diverse community of bacteria and yeasts.
Other cultured dairy foods include Greek yogurt, skyr and cultured buttermilk — maślanka. Their microbial composition depends on the cultures used and how the final product is processed.
Importantly, a fermented food containing live microorganisms is not automatically probiotic.
Probiotics are specific live microorganisms that have demonstrated a health benefit when consumed in an adequate amount.
How can fermented foods interact with the gut microbiome?
Live microorganisms from some fermented foods can pass through the digestive tract and interact with microorganisms already living there.
They do not necessarily become permanent residents of the gut.
Fermentation can also change the food itself.
Microorganisms produce organic acids and other biologically active compounds as they transform food. Some of these compounds remain in the final product and may interact with the gut environment.
This means that fermented foods can differ in both the microorganisms they contain and the compounds created during fermentation.
What does human research show?
Human intervention research suggests that a diet rich in a variety of fermented foods can influence the gut microbiome and immune activity.
In one clinical study, increasing fermented food intake was associated with increased microbiome diversity and changes in markers of immune activity.
However, this does not establish that yogurt, kefir, skyr or another individual fermented food produces the same effect.
The response may depend on the food, the microorganisms involved, the amount consumed and the individual’s existing gut microbiome.
Fermented foods are also only one part of a microbiome-supportive diet.
Vegetables, fruits, legumes, whole grains, nuts and seeds provide different types of fiber that can be used by microorganisms already living in the gut.
