Fermented Foods and Health

Kathryn Adel December 4, 2025 Diabetes, FODMAP, gastrointestinal health, Health, Heart Health, Weight Loss

Fermentation has long been a staple in traditional diets around the world. However, with urbanization, modern preservation techniques, and the rise of ultra-processed foods, the intake of fermented foods has declined in many industrialized countries, including Canada and the United States. Today, an expanding body of research highlights that fermentation not only preserves food but also provides numerous health benefits.

What are fermented foods?

Fermented foods are foods or beverages produced by the action of microorganisms (like bacteria or yeast) that break down food in the absence of oxygen, altering its chemical composition and creating byproducts (e.g., organic acids, alcohol, gas, carbon dioxide, postbiotics). The accumulation of these byproducts creates an environment favorable to beneficial microorganisms, prevents the proliferation of pathogens, and prevents food spoilage. This is why fermented foods last longer and develop tangy, pungent, or effervescent flavors. There are hundreds of fermented foods found in various cultures around the world, including kimchi, sauerkraut, kefir, miso, tempeh, natto, kombucha, and sourdough bread.

Fermentation can generate new beneficial compounds in foods. During fermentation, bacteria synthesize vitamins and other bioactive compounds. For example, the bacteria present in fermented foods can produce B vitamins (such as folate, vitamin B12, and riboflavin) and vitamin K during their growth. Similarly, some fermented vegetables have increased levels of vitamin C. Fermentation also improves the bioavailability of certain nutrients, making them more easily absorbed. For example, the fermentation of sourdough bread breaks down phytates, thus allowing for better absorption of iron, zinc, and magnesium by the intestine. Finally, fermentation can improve the digestibility of certain foods, particularly by reducing their FODMAP* content, which are fermentable sugars. For example, sourdough bread is lower in FODMAPs than regular bread and therefore easier to digest for people with irritable bowel syndrome (IBS).

Postbiotics and “Zombie Probiotics”

Postbiotics are the products that beneficial bacteria (probiotics) produce when they eat and multiply, such as anti-inflammatory metabolites, cell fragments, short-chain fatty acids, and enzymes. Even if cooking or pasteurization destroys the live bacteria, the postbiotics persist. These substances can have beneficial health effects even when the bacteria themselves are no longer alive. But scientists have discovered that even the dead bacteria themselves can be beneficial. These “zombie” probiotics can still modulate the immune system, strengthen the intestinal barrier, and reduce inflammation.

Thus, cooked or pasteurized fermented foods are still beneficial to health. Take sourdough bread, for example. Raw sourdough contains live lactic acid bacteria and yeast. During dough fermentation, the bacteria produce postbiotics such as organic acids, enzymes, vitamins, and metabolites that alter the texture, digestibility, and shelf life. During baking, the bacteria and yeast die, but their cell wall fragments, proteins, peptides, DNA, and other components remain present in the bread. These fragments can still modulate the immune response, have beneficial effects on digestion, and indirectly feed the gut microbiome. In short, dead bacteria remain useful: this is why we figuratively call them “zombie probiotics”.

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Author

Kathryn Adel

Kathryn holds a Bachelor Degree in Nutrition as well as a Bachelor and a Master Degree in Kinesiology, all from Laval University. She is a Registered Dietitian and active member of the Ordre professionnel des Diététistes Nutritionnistes du Québec (ODNQ) and of the American Academy of Nutrition and Dietetics. She holds the Monash University's certification for the FODMAP diet and IBS, and has considerable clinical experience in that area. She is also an accomplished athlete, having ran track and cross-country at a national level. Kathryn specializes in sports nutrition, weight loss, diabetes, as well as heart and gastrointestinal health.