Fermented foods: from ancient tradition to modern health ally
Food fermentation is an ancient practice. Long before refrigeration existed, people from different cultures used this process to preserve food, enhance flavor, and even neutralize toxins. Classic examples that remain part of our diets today include sourdough bread, beer, yogurt, sauerkraut, and kefir. With 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 transform 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 as “foods made through desired microbial growth and enzymatic conversions of food components.”
Inside fermentation: what microbes really do
Understanding what microorganisms do during fermentation helps explain why these foods have attracted scientific interest. Fermentations vary according to the agents involved in the process and the products that result from it. Different microorganisms drive distinct processes, leading to various 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 fungi may release ammonia.
In some cases, these microorganisms remain alive at the time of consumption, as in certain fermented milks; in others, such as sourdough bread and wine, they are eliminated.
The value of fermented foods goes beyond enhancing the flavors and textures of foods, as these food staples can:
- Be a source of beneficial live and active microorganisms.
- Improve the flavor, texture, and digestibility of foods.
- Increase the concentrations of vitamins and bioactive compounds in foods.
- Remove or reduce toxic substances or antinutrients present in raw foods.
- Inhibit pathogens and microorganisms that spoil food.
- Benefit 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 produce, may improve nutrient digestibility and absorption, compete with pathogens, strengthen the gut barrier, support the immune system, and reduce intestinal inflammation. The latest findings showed eating six servings a day of fermented foods, including yogurt, sauerkraut, kefir, kombucha and kimchi, may 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 gut” means the same thing
It’s 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 may also contain compounds with a prebiotic effect and generate postbiotic compounds. The reality is that a fermented food is a combination of nutrients, beneficial microbes, prebiotics, synbiotics, postbiotics, and microbe-derived compounds, while current science does not allow us to know which specific food component or combination of components are involved for the observed health benefits.
Here’s how these terms differ:
- Fermented foods: undergo transformation by microorganisms. They may or may not contain live microbes in sufficient amounts to bring health benefits.
- Prebiotics: fibers and other non-digestible compounds that serve as “food” for beneficial gut bacteria, helping them grow and thrive (examples: fructooligosaccharides (FOS), galactooligosaccharides (GOS), inulin).
- Probiotics: specific strains of live microorganisms (bacteria or yeasts) that, when consumed in adequate doses, have proven health benefits.
- Postbiotics: products of microbial activity, such as short-chain fatty acids or antimicrobial peptides, which may exert positive effects even in the absence of live microorganisms.
One common misconception is assuming that all fermented foods are probiotics. To ensure the fermented foods you buy contain probiotics, read the packaging and look for statements like “contains probiotics” or “contains live cultures” or look for the probiotic strains on the label. Also, if a fermented food is kept refrigerated at grocery stores means it is a source of live beneficial microbes.
It’s also important to highlight that fermented foods are not always a healthy option for everybody. For instance, kombucha is considered an alcoholic drink and due to the possibility of side effects, its consumption is contraindicated in pregnant women, infants, children under 4-years-old, patients with kidney failure, and patients with HIV.
Where science is headed next
Interest in fermented foods is on the rise, blending cultural tradition with scientific advances. Although many mechanisms still need to be clarified — such as nutrient bioavailability, the role of bioactive compounds, and vitamin production — recent evidence continues to highlight their potential as allies of nutrition and health, just as our ancestors intuitively recognized.
At the same time, products containing microorganisms require special attention to safety, especially when made at home (e.g., high temperatures and poor cleaned hands or utensils to prepare the fermented food blend 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 preservation practices to protect consumer health.
References:
Caffrey EB, Perelman D, Ward CP, Sonnenburg ED, Gardner CD, Sonnenburg JL. Unpacking Food Fermentation: Clinically Relevant Tools for Fermented Food Identification and Consumption. 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. doi: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
