In the Know: Fermented Foods

Fermented foods are increasingly recognized for their potential impact on gut health, assumed to stem from their rich content of probiotics, beneficial bacteria and bioactive compounds. These foods can vary widely in their microbial composition, which raises the question: how do different types of fermentation influence our microbiomes? Here, we’ll take a closer look at the science behind fermented foods, examining their possible benefits and limitations. We’ll explore how different fermented foods may interact with your unique gut microbiome, and discuss which options might be most effective depending on your individual needs.

What occurs during fermentation? Fermentation is a process in which bacteria and yeast convert sugars without utilization of oxygen, which can yield organic acids or alcohols. The environment that is thereby created is inhospitable to the typical microorganisms that cause food spoilage, so fermented products can have a generally longer shelf life.

There are a few different ways that fermented foods have been postulated to be beneficial to our health, including: the bioactive compounds generated from the fermentation process, the nutrients provided for other "indigenous" gut microbes, and the capacity of the available organisms from fermented food to survive transit through the stomach – either to contribute to the gut microbiome or compete with the existing organisms. 

Because of this, fermented products come with their own ecosystem of bacteria and yeast. Depending on the food, these organisms will be in a different balance, but common bacteria found in fermented foods include Lactobacillus, a type of bacteria, and brewer’s yeast (Saccharomyces cerevisiae). For example: in the brewing process for kombucha, the bacteria that ferment the sugars team up with the yeast to form a protective film on top of the drink, which serves the dual purpose of exposing some microbes to the oxygen and protecting the liquid from contamination by unwelcome microbes. When the yeast cells in kombucha die, they release nutrients that feed their bacterial teammates.

On a microbial level, depending on the type of fermentation, substrate, and microorganisms involved, the end products may vary. For example, Acetic Acid fermentation, which has Ethanol as a substrate, utilizes Saccharomyces cerevisiae and Zymomonas mobilis to produce Acetic Acid, which is vinegar, giving that distinctive taste you may recognize from some fermented items. Different compounds can be produced depending on the microorganisms present.

In terms of fermented foods, the Lactic Acid pathway is the most prominent, as it acts as the basis of all dairy fermentation and the majority of all pathways including plant and animal products. The lactic acid produced from the fermentation of cheese protects the cheese from degradation and also augments its flavor.

A few studies have been conducted showing the impact of the consumption of fermented foods on the gut microbiome. An observational study saw that there was an increased abundance of Akkermansia muciniphila following fermented foods consumption, known as a “next-generation probiotic” and increase gut barrier function as well as ameliorate poor metabolic symptoms. 

Another study showed that based on stool samples, yogurt consumers also presented higher levels of Akkermansia Muciniphila and increased levels of SCFA’s, such as butyrate and acetate, regulators of important biological processes and metabolism. In yogurt, the traditional cultures are Lactobacillus bulgaricus and Streptococcus thermophilus, known to aid in lactose digestion.

An longitudinal study was also conducted comparing a high-fiber diet vs. fermented diet on the human microbiome and immune system over 17 weeks. The high-fermented-food diet increased microbiome diversity and decreased inflammatory markers. These results suggest that fermented foods may help improve microbiome diversity and reduce inflammation, which is often low in industrialized societies.

On some level, along with genetics, everyone is a product of their environment.

Fermented products aren't one size fits all and although we most commonly see fermented dairy products, there is a whole wide world of other fermented items. Since many people avoid dairy or have other dietary restrictions, alternative options are provided for them. A study looked at the South Korean side dish, kimchi, and its consumption in prediabetic individuals, where it was observed that it lowered insulin resistance and glucose tolerance increased. 

When we get more specific into certain communities of individuals, we can look into a study done with diabetic pregnant women. The women, located in Iran, consumed probiotic yogurt for 9 weeks, where it was observed that the serum insulin levels were maintained, preventing them from developing insulin sensitivity.

Many different areas of the world offer different types of fermented foods, some fermented by various fermentation processes. Here are a few:

Mexico offers a wealth of fermented beverages. One prominent example is Tepache, a fermented drink made from pineapple rind, sweetened with brown sugar and seasoned with cinnamon. Another staple is Pulque, a mildly alcoholic drink derived from the fermented sap of the agave plant. White in color and slightly viscous, pulque’s history stretches back more than 4,000 years to the Otomi civilization in what is now Mexico. In its original context, pulque had ritual importance and was considered a means of communicating with the spiritual world. Today, you can find it in Pulquerías across Mexico City. 

Eastern Europe boasts a rich tradition of fermented foods, with sauerkraut and kefir being particularly noteworthy. Sauerkraut, made from fermented cabbage, is a popular condiment in Germany and Poland, where its briny flavor cuts through heavier meat or starch dishes. Making sauerkraut involves thinly slicing and bruising the cabbage leaves to release their liquid, then allowing them to brine for a few weeks. 

Kefir, a fermented milk drink originating from the Caucasus region, is renowned for its probiotic properties as it’s a good source of Lactobacillus and Bifidobacterium. Kefir is made by introducing grains of bacteria and yeast suspended in a sugar mixture into milk and allowing it to ferment at room temperature. The result is a thick, yogurt-like drink filled with fermentation products like lactate. You can find kefir bottled in many Western grocery stores, or if you’re feeling adventurous, you can buy the grains online and try making it yourself.

Fermented foods and probiotics are both made from microorganisms, however it's important to note that only probiotics are capable of delivering proven health benefits when taken correctly. Fermented foods may or may not contain probiotics, and the term “probiotic” should only be used when there is clear health benefits conferred by characterized live microorganisms. However, evidence for such benefits remain rare and contentious. 

A study involving a clinical trial where participants received a 10-day course of broad-spectrum antibiotics was conducted. These antibiotics significantly reduced gut microbial diversity, with specific bacteria like Bacteroides and Firmicutes decreasing notably. After the antibiotic treatment, some participants were given probiotics to assess their ability to aid recovery. While probiotics helped accelerate the recovery process, the study found they were only partially effective in restoring the microbiome, with strain-specific effects observed. It was concluded that probiotics could support gut health, but they were not sufficient to fully restore pre-antibiotic microbial diversity, emphasizing the need for more targeted probiotic treatments. 

The same study shows that different individuals respond variably to probiotic supplementation in terms of colonization in the gastrointestinal (GI) tract. Probiotics do not always colonize the gut equally across all people. Factors such as an individual's pre-existing gut microbiome, genetics, diet, and overall health can influence how well probiotics establish themselves in the GI tract. While some individuals may experience significant colonization and benefit from probiotic use, others may show little to no effect. These inter-individual differences underline the complexity of probiotic treatments and suggest that a personalized approach may be necessary for optimal outcomes.