Fermented foods: from age-old tradition to modern health ally
Food fermentation is one age-old practice. Long before refrigeration existed, people from different cultures used this process storing food, improve tasteand even neutralize toxins. Classic examples that are still part of our diet today are sourdough bread, beer, yogurt, sauerkraut and kefir. Thanks to technological advances, hundreds of types of fermented foods are now produced on a global scale.
Simply put, fermentation occurs when microorganisms such as bacteria and yeast convert the starches and sugars in food into alcohol, lactic acid, carbon dioxide and other compounds. The International Scientific Association of Probiotics and Prebiotics (ISAPP) defines fermented foods like “foods made by desirable microbial growth and enzymatic conversions of food components.”
Indoor fermentation: what microbes really do
Understanding what microorganisms do during fermentation helps explain why these foods have attracted scientific interest. Fermentations vary depending on the agents involved in the process and the products that result. Different microorganisms control different processes, leading to different changes, such as the production of acids, alcohols, gases and other metabolites — for example: lactic acid bacteria produce lactic acid, yeasts generate alcohol and carbon dioxide, acetic acid bacteria produce acetic acid, and molds can release ammonia.
In some cases, these microorganisms remain alive at the time of consumption, such as in certain fermented milks; in others, such as sourdough bread and wine, they are eliminated.
The value of fermented foods goes beyond improving the flavors and textures of food these food staples can:
- Be a source of beneficial living and active microorganisms.
- Improve the taste, texture and digestibility of food.
- Increase the concentrations of vitamins and bioactive substances in foods.
- Remove or reduce toxins or antinutrients present in raw foods.
- Inhibit pathogens and microorganisms that spoil food.
- It benefits human health by reducing the risk of certain acute and chronic diseases.
Scientists are actively investigating the potential health benefits of specific fermented foods. The microorganisms themselves, or the components they producecan improve digestibility and absorption of nutrients, compete with pathogens, strengthen the intestinal barrier, support the immune system and reduce intestinal inflammation. The latest findings showed Eating six servings of fermented foods per day, including yogurt, sauerkraut, kefir, kombucha and kimchi, can improve the diversity of the gut microbiome and reduce body-wide inflammation, which is linked to a range of chronic diseases.
Not everything labeled as ‘good for the intestines’ means the same
It is important to note that although fermented foods may contain live and active cultures, this does not mean they meet the definition of a probiotic. In addition, fermented foods can also contain compounds with a prebiotic effect and generate postbiotic compounds. The reality is that fermented foods are a combination of nutrients, beneficial microbes, prebiotics, synbiotics, postbiotics and microbe-derived compounds, while current science does not allow us to know which specific dietary component or combination of components plays a role in the observed health benefits.
Here’s how these terms differ:
- Fermented foods: undergo transformation by microorganisms. They may or may not contain enough living microbes to provide health benefits.
- Prebiotics: fiber and other non-digestible compounds that serve as “food” for beneficial intestinal bacteria, allowing them to grow and flourish (examples: fructooligosaccharides (FOS), galactooligosaccharides (GOS), inulin).
- Probiotics: specific strains of living microorganisms (bacteria or yeast) that, when consumed in adequate doses, have proven health benefits.
- Postbiotics: products with microbial activity, such as short-chain fatty acids or antimicrobial peptides, which can have positive effects even in the absence of living microorganisms.
A common misconception is the assumption that all fermented foods are probiotics. To make sure the fermented food you buy contains probiotics, read the packaging and look for statements like “contains probiotics” or “contains live cultures” or look for the probiotic strains on the label. Keeping fermented foods refrigerated in grocery stores also means they are a source of living, beneficial microbes.
It’s also important to emphasize that fermented foods are not always a healthy option for everyone. For example, kombucha is considered an alcoholic drink and because of the potential for side effects its consumption is contraindicated in pregnant women, infants, children under 4 years of age, patients with renal failure and patients with HIV.
Where science goes next
Interested in fermented foods are on the risecombining cultural tradition with scientific progress. Although many mechanisms remain to be elucidated – such as nutrient bioavailability, the role of bioactive compounds and vitamin production – recent evidence continues to emphasize them potential as allies of nutrition and healthjust as our ancestors intuitively recognized.
At the same time, products containing microorganisms require special attention to safetyespecially when prepared at home (for example, high temperatures and poorly cleaned hands or utensils used to prepare the fermented food mixture allow harmful bacteria to grow, leading to foodborne illness). For this reason, it is essential that scientific progress goes hand in hand with regulation, ensuring clear labeling and good storage practices protect consumer health.
References:
Caffrey EB, Perelman D, Ward CP, Sonnenburg ED, Gardner CD, Sonnenburg JL. Unpacking food fermentation: clinically relevant tools for the identification and consumption of fermented foods. Adv Nutr. 2025;16(5):100412. doi:10.1016/j.advnut.2025.100412
Caffrey EB, Sonnenburg JL, Devkota S. Our extended microbiome: the human-relevant metabolites and biology of fermented foods. Cell Metab. 2024; 36(4):684-701. Two: 10.1016/J.cmet.2024.03.007
Mukherjee A, Breselge S, Dimidi E, Marco ML, Cotter PD. Fermented foods and gastrointestinal health: underlying mechanisms. Nat Rev Gastroenterol Hepatol. 2024;21(4):248-266. doi:10.1038/s41575-023-00869-x
Pyo Y, Kwon KH, Jung YJ. Probiotic functions in fermented foods: antiviral, immunomodulatory, and anticancer benefits. Foods. 2024;13(15):2386. doi:10.3390/foods13152386
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