There is a growing body of research surrounding the role of diet and gut health including the role of fermented foods, such as yoghurt, in promoting a healthy digestive system.
Growing research supports the role of gut health in overall health and wellbeing. The gut microbiome (the collective term for microorganisms and their genetic material that live in the digestive system) plays an important role in digesting food and absorbing nutrients [i]. In recent years, the gut microbiome has been linked to the development of conditions such as obesity [ii] and inflammatory bowel disease [iii].
The foods we eat play an essential role in maintaining the diversity and proper functioning of our gut [iv]. There is a growing body of research around the role of diet and gut health, and this includes the role of fermented foods in promoting a healthy digestive system.
What is it about fermented foods that contribute to health?
Historically, fermentation has been used as a traditional method of preserving food. This process involves the conversion of raw foods via the metabolic activity of microorganisms. For example, live cultures (a blend of one type or several strains of microorganisms) help transform milk into yoghurt.
As the ‘good’ bacteria multiply, they produce compounds that change the characteristics of the product including flavour, texture and nutrients. The fermentation process can also alter the nutritive and bioactive properties of foods that can benefit health [v].
Some fermented foods contain probiotics; active bacterial cultures with unique characteristics that allow them to survive in the gastrointestinal tract. When consumed in adequate amounts, they provide a health benefit [vi] and have the potential to maintain the natural balance of the gut microbiota.
What foods contain probiotics?
Nowadays, probiotics are easily incorporated into the daily diet. Fermented dairy products such as yoghurt, culture drinks and kefir are some of the most common and easily available sources of probiotics. Other fermented foods and drinks include kombucha, sauerkraut and kimchi.
Fermented dairy foods are a common vehicle for probiotics as the composition of milk (which includes protein and fat) acts as a protective matrix to help the survival of probiotics from the digestive system through to the gut, including the adverse conditions of the stomach [vii].
Not all fermented products however have demonstrated beneficial effects on health. It will depend on the presence of living ferment and the type of ferments provided by the products, together with the ability to survive the acidic conditions of the stomach and reach the intestines alive. Particular strains of probiotics may also have different beneficial effects in the body.
What's the science around dairy and gut health
The most commonly studied fermented dairy product in relation to gut health is yoghurt.
To see a benefit on the gut microbiome, a key measure of its effectiveness is that the beneficial bacteria must be able to survive the transit through the gastrointestinal system. Studies have investigated the viability of probiotics in yoghurt and fermented milk, reporting increased recovery of bacteria in fecal samples [viii],[ix].
Following yoghurt consumption, another study has reported a slight increase in microbial diversity in some individuals [x], while increases in beneficial gut bacteria (Bifidobacteria and Lactobacilli) have also been observed with several different types of probiotics [xi]. Daily consumption of a probiotic yoghurt is also thought to decrease pathogens in the gut [xii].
Some have argued that probiotics in yoghurt are unlikely to have any health effect as it has not yet been determined whether they colonise in the gut. There are still many knowledge gaps in relation to the way dairy products might affect the composition of the intestinal microbiota and we are learning more about the role of diet and gut health.
One of the most scientifically recognised health benefits related to dairy and gut health is yoghurt's role in managing lactose maldigestion. It appears yoghurt is better tolerated when compared with milk, and this is a likely consequence of the live bacteria within the product [xiii]. In addition, the unique yoghurt matrix results in a longer gastrointestinal transit time than that for milk, helping with the absorption of nutrients and reducing gastrointestinal upsets [xiv].