4 January 2018
I regularly make my own fermented foods, such as kombucha, sourdough, as well as other plant based experiments; they’ve become something of a hobby of mine, I love their unique flavour and the simple way they extend the shelf-life of fresh produce.
And it seems I’m not alone as fermented foods were cited as one of the one of the key food trends in 2017. New research into their potential health benefits has also been increasing; in the last 40 years scientific publications have increased dramatically (11 in 1977 to 755 in 2017, according to Pubmed). Being an avid fermentation enthusiast I was keen to explore this area further.
What exactly is a fermented food?
Fermentation is the bacterial (or yeast) conversion of sugar and starch to acids and other by-products, including ethanol. The acidity not only prevents growth of food spoilage bacteria -fermentation has been used as a food preservation method for thousands of years - but also creates foods with unique sour, tangy flavours.
Popular fermented products include yogurt, beer and bread. Increasingly found on our supermarket shelves though are fermented foods traditionally consumed in other parts of the world; sauerkraut (‘sour cabbage’) from Germany, kombucha originally from China, kimchi from Korea and kefir from the Caucasian mountains.
Products that are subsequently processed by heat, baking or filtration (e.g. pasteurised sauerkraut, sourdough) inactivate or remove the microbes in fermented foods, and so will not contain live cultures.
A probiotic benefit?
The potential benefits of fermented foods have been widely heralded in the popular media. The main area of research with regards to their health benefits is in the probiotic content; probiotics are defined as live microorganisms that can establish within the gut and confer a benefit to the host. Although there are currently no authorised European health claims for probiotics, there is a growing recognition for the importance of the gut microbiota, both for gut and non-gut health outcomes.
However, the beneficial effects of probiotics are strictly strain-specific and the strain composition and stability of the microbes in fermented foods is not well understood. Experts have concluded that fermented foods with unidentified microbial content cannot be considered probiotics. Furthermore, it is not always possible to clearly distinguish the potential contribution of the microbial content from that of the food matrix - in other words could the health benefit be associated with other aspects of the food, rather than the microbes?
What is the scientific evidence?
A number of in vitro and animal studies, using fermented foods such as sauerkraut and kombucha, report encouraging results. But more detailed reading indicates that researchers often use an extracted fraction of the fermented food or an isolated bacterial strain from them. Furthermore there is only a limited evidence base for fermented foods and health in humans. In cohort studies yogurt and other fermented dairy foods have been associated with health benefits; however no causal links can be drawn from this type of study. A very small number of controlled human trials using kimchi, kefir and other fermented dairy products have reported improvements in some health parameters. Nevertheless, these studies don’t always use a suitable control, are often carried out with small groups of individuals and do not always represent the fermented foods that are available.
The limitations and inconsistencies in the current body of evidence mean that, to date, no definitive conclusions can be drawn about potential health benefits of fermented food.
There are some other interesting areas of research though. For example it is suggested that fermentation can increase the iron bioavailability from cereals by reducing phytic acid content, which can stop your body absorbing iron. Certain bacteria can also synthesise nutritive compounds, including particular B vitamins. However, other bacterial species may utilise these nutrients so overall we don’t know if such changes could be clinically relevant.
Should we all be eating fermented foods?
Fermented foods can be incorporated as part of a balanced, healthy diet, although it should be recognised that some, such as sauerkraut and kimchi, can have a high salt content. For those wanting to ferment at home do ensure you follow food hygiene practices and that you use the correct ingredients, conditions and storage practices for that particular ferment. Although the evidence for specific health benefits is not currently convincing, I am thoroughly convinced of the taste, saving on food waste and fun benefits! And will watch the evidence base with interest.