If you’ve been scrolling through social media lately, delving into the world of food and nutrition, no doubt you’ve come across many health professionals singing the praises of fermented foods. But what exactly is fermentation? Why are fermented foods good for you? And should you be eating them on the regular?

In this post I’ll talk about the process of fermentation, how fermented foods benefit the body, and examples of every-day fermented foods you can incorporate into your diet.

What is fermentation?

Fermentation is the process by which sugars are broken down by microorganisms (e.g. bacteria) in the absence of oxygen. To explain the process, I’m going to have to get a bit sciencey for a second:

The fermentation process

Cellular respiration is the controlled release of energy from organic compounds (glucose being the main one) in cells to form ATP (the principal molecule for storing and transferring energy in cells).

Glycolysis is the first stage of cellular respiration and involves the breakdown of glucose (a 6 carbon molecule) into two molecules of pyruvate (a 3 carbon molecule). There are two types of cellular respiration, aerobic which involves the presence of oxygen and anaerobic which doesn’t involve oxygen. 

In the presence of oxygen, aerobic respiration uses NADH, an electron carrier molecule, to produce large amounts of ATP, releasing NAD+ which can be reused to form NADH, thus continuing the cycle.

However, in the absence of oxygen, such is the case with anaerobic respiration, the NADH remains idle and cannot be used to release NAD+ (needs oxygen to do this). This means glycolysis cannot continue to occur (no spare NAD+) and no further ATP can be produced. 

Fortunately, there are ways to get around this. The NADH from glycolysis are now used to produce 2 ethanol and 2 carbon dioxide molecules in plants or lactic acid in animals. How does this work?

The two pyruvate molecules are converted into a temporary by-product (lactic acid or ethanol) in a reaction that uses NADH to release NAD+. This allows for low amounts of ATP to be produced via glycolysis as there is now free stock of NAD+.

Lactic acid fermentation is commonly used in the production of foods like yogurt, pickles, and sauerkraut, giving them their classic tangy flavour where ethanol fermentation is used to produce wine and beer, as well as bread. Generally, anything that uses microbes to transform simple ingredients can be regarded as fermented food.

How do fermented foods benefit the body?

While there are a large number of anecdotal claims for the purported health benefits of fermented food, the hard science is lacking (the exception being fermented dairy, where there is ample evidence of health-promoting benefits (1) (2)). That being said, researchers are starting to unravel the ways in which other fermented products are connected to the gut along with health benefits that can ensue.

Microbial diversity is king when it comes to benefiting our guts and the types of food we eat can have a marked influence on the variety of microbial inhabitations. Fermented foods in their raw, unpasteurised form, boost healthy bacterial strains in our body and have been shown to provide beneficial health effects.

A new study conducted by researchers at the Stanford School of Medicine (3) has found that a diet rich in fermented foods could lead to a greater gut microbiome diversity and a reduction in some markers of inflammation, commonly linked with conditions such as type two diabetes, rheumatoid arthritis and chronic stress.

Fibre, a popular choice on the microbial menu, helps our microbes thrive. Processed foods and reduced fibre intake, in contrast, are thought to decrease microbial diversity, dietary features all too common in western societies. The study by the researchers at Stanford also found that while increasing fibre did not impact gut microbiota diversity, it did lead to immune regulating changes through increased production of short-chain fatty acids (SCFAs); a metabolite that plays an important role in boosting immunity (4).

Reductions in inflammation on the high fibre diet were predominantly seen in those who started out with higher levels of microbial diversity compared to those with lower microbial diversity actually had slight increases in inflammation when they consumed more fibre, showing the importance of gut diversity in gaining the full benefits of fibre in the diet.

A final reason why fermented foods may be favourable is that during fermentation, a range of health-promoting compounds such as vitamins and organic acids are produced by the microbes. This means when you eat a fermented food, you’re also consuming all those healthy, microbial-produced nutrients.

Examples of fermented foods

Yogurt: a well known creamy and versatile milk product that has been linked with a reduced risk of breast cancer, colon cancer, type 2 diabetes, and better cardiovascular, bone and gut health (5). Dollop on porridge, add to smoothies, serve with berries, make into a sauce, the choices are endless.

Milk Kefir: a type of fermented dairy product made by adding kefir grains, bacteria and yeast cultures to milk. With a similar taste to yogurt, kefir can be eaten with fruit, poured on cereal / muesli, added to smoothies, or drunk chilled from a glass

Kombucha: a fizzy fermented drink made with black or green tea, sugar, bacteria and yeast. Highly refreshing, kombucha is the perfect drink for a hot summer’s day

Kimchi: a common Korean cuisine, this product is made from fermented vegetables like cabbage and radish

Miso: adding a salty umami flavour to many Japanese dishes, this product is made from fermenting soybeans with salt and koji (a type of mold). Most commonly used as an ingredient in soup, it can also be spread on pizzas or made into a miso butter – great for coating veggies or smearing on toasted bread

Sauerkraut: consumed for thousands of years, this fermented food is made from shredded cabbage, salt and spices. It has a crunchy texture making it the perfect topping on hotdogs or baked potatoes, served with fish or added to a sandwich

Most fermented foods contribute live bacteria that have a potential probiotic effect. For bacteria in fermented foods to have a chance to provide health benefits to the body, they must be able to survive all the way through the gut to the bowel and the colon. Unfortunately, this is not always guaranteed, and the probiotics (good bacteria) need to be eaten regularly and in large numbers to survive the journey.

If they make it all the way to their new home, these microbes play a beneficial role in health, making fermented food yet another useful tool in the diet toolbox.

Is fermented food safe for everyone?

While fermented foods are indeed safe for the majority of people, those who suffer from histamine intolerance may experience unwanted side-effects. Also, those who aren’t used to eating fermented food may want to start off slowly in order to avoid the wind and bloating that can result from the microbes doing their thing. Finally, those who are critically ill, immune-compromised or pregnant should check with a GP or health professional before consuming fermented products.

Conclusion

The fact that small changes to the diet, in the form of incorporating fermented products alongside fibre, can significantly shape the gut microbiome which in turn can affect the immune system is quite exciting. While not a panacea for health on its own, incorporating fermented products into your diet may reduce your risk of developing a number of long-term unhealthy conditions, and, at the very least, adds a delicious little tang to your meal.

Brigid xx

References

(1) González, S et al. “Fermented Dairy Foods: Impact on Intestinal Microbiota and Health-Linked Biomarkers.” Frontiers in microbiology  vol. 10 1046. 24 May. 2019, doi:10.3389/fmicb.2019.01046

(2) Veiga, P., Pons, N., Agrawal, A. et al. Changes of the human gut microbiome induced by a fermented milk product. Sci Rep 4, 6328 (2014). https://doi.org/10.1038/srep06328

(3) Wastyk HC, Fragiadakis GK, Perelman D, Dahan D, Merrill BD, Yu FB, Topf M, Gonzalez CG, Van Treuren W, Han S, Robinson JL, Elias JE, Sonnenburg ED, Gardner CD, Sonnenburg JL. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021 Aug 5;184(16):4137-4153.e14. doi: 10.1016/j.cell.2021.06.019. Epub 2021 Jul 12. PMID: 34256014.

(4) Yamamoto, Shinya et al. “The human microbiome and COVID-19: A systematic review.” PloS one vol. 16,6 e0253293. 23 June. 2021, doi:10.1371/journal.pone.0253293

(5) Savaiano DA, Hutkins RW. Yogurt, cultured fermented milk, and health: a systematic review. Nutr Rev. 2021 Apr 7;79(5):599-614. doi: 10.1093/nutrit/nuaa013. PMID: 32447398; PMCID: PMC8579104