Fermented Food as Probiotics: Health Perceptions and Research
Posted 25th July 2018 by Jane Williams
As a microbiologist in the field of probiotics, I am often asked, “Will probiotics improve my health?” I always give the same answer: studies show specific benefits of probiotics for certain conditions, but there is not conclusive evidence that they will improve health for an already healthy person.
I know this is an unsatisfying answer. It is a careful answer and one that relies on the tenets of scientific research – large samples sizes, causation over correlation and repetition of experimental results. At this point, I cannot say with confidence that research supports the idea that ingesting a certain probiotic can make you a healthier person.
What this answer does not mean is that there are no potential health benefits. There are some real possible benefits to probiotics. Probiotics is a very broad term, but fermented products, which contain rich communities of bacteria, have been gaining popularity. Sales of fermented drinks, including kombucha and apple cider vinegar, were up 37.4% in 2017, and are expected to continue to increase. 
These fermented drinks can be, and often are, produced at home, although, as the numbers above reveal, they also represent an important market in the food industry.
What are Fermented Foods?
Fermentation is a metabolic process by which sugars are broken down by the cell without requiring oxygen. Fermented foods are part of the traditional diet from many different regions of the world and have a long history in many cultures. Beyond the potential as a probiotic, they have the benefit of having vitamins and minerals that make up a healthy diet.
The production of fermented foods is varied. For example, apple cider vinegar may be produced with different types of apples, or kombucha might be prepared with the addition of another product, such as vinegar. These variations in the ingredients and process can influence the makeup of the bacterial community that is eventually ingested. This complicated the study of the health benefits of fermented products. Opening up the possibility of various methods produces novel health benefits that are not seen broadly across a single category of food.
Two of the more popular fermented foods that are consumed and sold include apple cider vinegar and kombucha.
Apple Cider Vinegar
Apple cider vinegar (ACV) is produced by fermenting apples. In this process, the sugars in the apples are broken down and acetic acid is produced, along with a vibrant bacterial community. ACV is more heterogeneous (has a higher diversity of bacterial species) than other vinegars. When looking for a probiotic, this diversity is a plus.  My own lab has confirmed that ACV, along with Kombucha, is more heterogeneous than other tested probiotics, including commercial probiotics. Organic ACV is even more heterogeneous than conventionally produced ACV. 
Vinegar has long been studied and linked to overall health benefits. As far as health benefits specific to ACV, animal studies show that diets that include ACV can improve the health profile of the animal in question. A study using rats indicated that the negative metabolic effects of a high fat diet may be countered by consumption of ACV, although the authors warn these results are preliminary.  Other mouse studies also show an effect on cholesterol and triglyceride levels.  Studies with fish show that a diet that includes ACV along with Lactobacillus casei improves health function as well. 
As with ACV, kombucha is produced via the fermentation process. The literature on kombucha is less extensive than that on vinegar or ACV. However, there is interest in kombucha and its potential health benefits.  One review of the literature does see some promising evidence that kombucha might play a role in preventive health benefits but warns that more research is needed to conclusively link the two. 
Unlike ACV, there is concern about the potential toxicity of kombucha. Sporadic cases of liver toxicity in patients have been connected to the consumption of kombucha, although a study from 2000 reported no toxic effects on rats. 
Positive health effects have been reported by several studies. These include reports that kombucha slows the growth of cancerous cells. Some of the negative metabolic health effects from breast cancer were mitigated by the consumption of ginger-based kombucha in mice.  Other types of kombucha were shown to have varying effects on cells in culture at preventing bacterial infection and slowing proliferation of growth.  Kombucha also exhibited antiviral effects in foot and mouth disease in swine.  Finally, multiple studies in rats have shown that kombucha has the potential to help with diabetes prevention and treatment by protecting liver-kidney function. 
In both ACV and kombucha, studies indicate that health benefits are enhanced when they are taken along with another form of lactobacilli.  Both of these fermented drinks showed similar bacterial profiles. The prominent genera were Acetobacter and Komagataeibacter.  Similar bacterial profiles would indicate that many of the health benefits between the two would overlap.
As sales and homemade production is expected to increase, there is clear need for more research into the potential health benefits of these and other fermented drinks and a further exploration of the conclusions by the studies described above.
Sandra Buerger is a lecturer at Boston University and Massachusetts General Hospital Institute of Health Professions.