Ferments are foods that have been transformed by the growth and metabolic activity of living microorganisms, including bacteria, yeast and even moulds. They include yoghurt, kefir and some cheeses, which are produced as a result of lactic acid bacteria feeding on the lactose and other nutrients in milk.
Many fermented foods are teeming with live microorganisms. Some of these foods, such as fresh kimchi and fresh sauerkraut, are populated by wild microorganisms (like a sourdough culture), while others, such as yoghurt, kefir and kombucha, typically have a culture of microorganisms added to initiate fermentation.
A number of these microorganisms will not survive the hostile environment of the digestive system, but studies show that many do. Survival capabilities and rates vary greatly depending on the strain of microbe. One example is this 2016 study from Gyeongnam National University of Science and Technology, which suggests a link between high kimchi consumption and a healthier composition of microbes.
According to researchers, our gut microbiota play an essential role in fermenting non-digestible fibres. This fermentation supports the growth of other specialist microbes that produce short-chain fatty acids. It is these fatty acids that scientists believe play a key role in the microbiota’s impact on health.
A 2017 review of the health benefits of fermented foods published in Current Opinion in Biotechnology references numerous studies suggesting links between fermented foods and our health. These include an association between consumption of fermented dairy and weight management, and potential anti-diabetic and anti-obesity benefits of kimchi. More work is needed to substantiate these findings.
Fermentation is thought to increase the levels of B vitamins available in foods, as well as the levels of antioxidants, according to a review of the health benefits of fermented foods. It is believed it can result in the removal of toxic or undesirable food constituents too.