Fermented foods belong in a gut-friendly diet

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If you haven’t yet jumped on the fermented-food wagon, you might consider adding these foods to your regular diet.

According to researchers from the Stanford School of Medicine, a diet rich in fermented foods – including kefir, kombucha and pickled vegetables – can improve gut health and reduce inflammation.

The study, albeit a small one, is one of the first to demonstrate how a minor change in diet can favourably alter the gut microbiome in healthy adults.

Gut microbiome diversity

Findings from many studies suggest the active microbial community that lives inside our large intestine – our gut microbiome – influences mood, mental health and appetite, as well as the risk for chronic diseases, including inflammatory bowel disease, asthma, Type 2 diabetes, cardiovascular disease and obesity.

It also communicates with our immune system – most of which resides in the gut, and as such influences inflammatory responses in the body. Chronic inflammation is recognized as a major determinant of many serious diseases.

Plenty of evidence has shown that what you eat – and don’t eat – shapes the diversity of the gut microbiome. Having a diverse population of gut microbes has been linked to better health.

Plant-based diets are tied to a richer and more diverse microbiome. Diets high in animal protein, refined carbohydrates and highly processed foods, on the other hand, are associated with reduced microbiome diversity.

Fermented foods vs. fibre

The study, published online last month in the journal Cell, assigned 36 healthy adults to one of two dietary interventions: a high-fermented-foods diet or a high-fibre diet. (High-fibre diets have been associated with a greater microbial diversity in the gut.)

Blood and stool samples were collected from the participants for three weeks leading up to the study, during the 10-week intervention and for four weeks after the study finished.

The high-fermented-food group increased daily intake of fermented foods from one-half of a serving at baseline to six servings by the end of the study. One serving was defined as six ounces of kombucha, yogurt, kefir or buttermilk; one-quarter of a cup of kimchi, unpasteurized sauerkraut or fermented vegetables; or two ounces of vegetable brine drink.

Those in the high-fibre group increased fibre intake throughout the study, from an average of 21 grams per day to 45 grams. Fibre came from whole grains, pulses, seeds, nuts, vegetables and fruits. (For perspective, the average Canadian consumes 16 to 18 grams of fibre per day.)

Eating fermented foods led to an overall increase in microbial diversity – the higher the intake, the greater the diversity. Levels of inflammatory proteins in the blood also decreased. These effects occurred in all participants in the high-fermented-food group.

The diversity of gut microbes remained stable, however, in the high-fibre eaters and their blood inflammatory markers didn’t drop. It’s possible that the study duration was too short for fibre to have an effect on microbial diversity.

Limitations of the study include its small number of participants, brief duration and the lack of a control group to compare each diet group to. Still, it adds important insights into the effect of diet on microbiome diversity and gut immune function.

Positively probiotic

Many, but not all, fermented foods are a source of probiotics – beneficial microbes that can help increase the population of gut microbes. Consuming probiotic-containing fermented foods may also enhance microbial diversity by causing shifts in the community of microbes that live in the gut.

Kefir (a yogurt-like drink sold in the dairy case), kimchi (a Korean side dish of fermented cabbage with seasonings), unpasteurized sauerkraut, vegetables pickled in brine (not vinegar), kombucha (a fermented tea beverage), miso and natto (both made from fermented soybeans) all contain probiotic cultures. Tempeh, also a fermented soy food, does not.

Probiotics aside, fermented foods have other nutritional benefits. During fermentation, microbes release vitamins and minerals from carbohydrates, making them more available for the body to absorb.

Fermented foods are also easier to digest. Fermenting milk, for instance, breaks down lactose – making kefir, yogurt and buttermilk more digestible for people with mild to moderate lactose intolerance.

Leslie Beck, a Toronto-based private-practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD.

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