The many health benefits of fermented foods

They may be in fashion, but fermented foods didn’t need influencers to make it onto the menu, with the earliest being produced in the Mediterranean region as far back as 14,000 B.C. ¹
Back then, trial and error revealed fermentation to be an excellent way to preserve food. It wasn’t until 1857 that Louis Pasteur discovered the mechanisms underlying the fermentation process and the role of living organisms (yeasts, bacteria and other microscopic organisms).

In the absence of oxygen, enzymes produced by these microorganisms break down components (often sugars) of the food, resulting in the creation of acids (lactic acid in yogurt, cheese, sauerkraut, kimchi, etc.) or alcohol (alcoholic fermentation in wine) in particular.
The acid lowers the pH and repels pathogens, as does alcohol, an antimicrobial agent. ²

Overview of the most common food fermentations

Source: Valentino, 2024 ²

Rich in microorganisms with probiotic effects 

Some fermented foods, such as bread, wine, coffee, or chocolate, no longer contain live microorganisms, since cooking or food processing has eliminated them. ¹
However, many foods are still teeming with live bacteria and yeast when consumed.
This is the case with:

• yogurt
• kefir
• most cheeses
• miso
• nattō
• tempeh
• unheated fermented vegetables such as pickles,
• as well as salami and other unheated sausages. ¹ 

These live microorganisms prevent the growth of pathogens such as the infamous Listeria or Salmonella, which cause food-borne illnesses. 

But the story doesn’t end at the cupboard door. When we consume fermented products containing live bacteria and yeast, we ingest these microorganisms, which pass through our digestive system.
Many perish in the acidic environment of our stomach, but some appear to reach our intestines and alter our microbiota, either temporarily, or long term when the food is consumed regularly. ^1,3,4,5

This is the probiotic (sidenote: Probiotics Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. FAO/OMS, Joint Food and Agriculture Organization of the United Nations/ World Health Organization. Working Group. Report on drafting  guidelines for the evaluation of probiotics in food, 2002. Hill C, Guarner F, Reid G, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014;11(8):506-514. ) effect of uncooked or unpasteurized fermented foods such as kombucha, kefir or kimchi, which enrich our gut flora with microorganisms beneficial to our digestive system (fight pathogens, strengthen our gut barrier, reduce inflammation, etc.) and our overall health. ² 

Rich in prebiotic fiber 

Fermented foods aren’t just a source of bacteria; they also feed these microorganisms.
For example, fruits, vegetables, and bread (especially whole-grain bread) contain dietary fiber, i.e., carbohydrates that our bodies can’t digest. ⁶ These fibers eventually reach our large intestine, where they’re consumed by our bacteria.

Fermentable dietary fibers from fruits, vegetables, and legumes, as well as non-fermentable fibers (such as resistant starch) from grains, all serve as substrates that nourish our gut microbiota ⁶ and function as prebiotics.
Thanks to them, our gut flora stays in top form. 

Rich in postbiotic metabolites 

Fermentation by bacteria—whether in sauerkraut, in cheese, or within our digestive tract—results in the production of numerous metabolites, including short-chain fatty acids (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) (SCFAs).
The most well-known of these is undoubtedly butyrate (sidenote: Butyrate A short-chain fatty acid produced by gut bacteria through fermentation of dietary fiber. ) , which boosts the intestinal barrier function of our digestive system by stimulating the production of protective mucus and proteins that bind together the cells of the intestinal wall.
Butyrate’s effects extend beyond the digestive system, since it enters our bloodstream and helps regulate certain bodily functions, for example, by increasing satiety or reducing inflammation. ⁷
Fermented foods thus have a postbiotic (sidenote: Postbiotics A preparation of inanimate microorganisms and/or their components that confers a health benefit on the host. Salminen S, Collado MC, Endo A, et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nat Rev Gastroenterol Hepatol. 2021 Sep;18(9):649-667. ) effect as well, which contributes to their health benefits! 

But that’s not all.
Microorganisms produce many other compounds beneficial to our health, including:

• vitamin B in fermented dairy products
• vitamins A, B, and C, minerals, and polyphenols in şalgam, a Turkish fermented drink made from black carrots and turnips;
• beneficial antioxidants in kombucha, a sweet, fermented tea;
• and polyphenols in Chinese fermented vegetables or red wine. ^1,3

Easier to digest, in every sense 

Fermented foods are also known to be easier to digest. Certain microorganisms, thanks to their own enzymes, do the hard work of digestion for us, breaking down the large molecules of carbohydrates, proteins, or fats into smaller, more digestible molecules.^1,3
Fermentation can also improve the bioavailability of certain nutrients. For example, in milk-containing products such as yogurt, calcium and potassium are easier to absorb. ² 

Fermentation can also make certain foods “tolerable” to those with intolerances.
The most classic example is lactase, an enzyme which digests lactose during childhood, but which is sometimes lost later in life. Its absence leads to lactose intolerance, which results in bloating at the slightest sip of milk.
Conversely, yogurt and cheese are often well tolerated. Why? Because lactic acid bacteria, thanks to their own lactase, have already broken down a large portion of the lactose, significantly reducing its concentration and the risk of intolerance.^1,2,3
Fermentation is also thought to reduce FODMAPs and gluten, somewhat improving tolerability in sensitive individuals. ⁸ 

Lastly, fermentation can also lower the concentration of antinutritional factors in foods.
In soy, it reduces the level of trypsin inhibitors, which block a pancreatic enzyme necessary for the digestion of proteins. ^1,3
Similarly, the fermentation of grains and legumes lowers the level of phytates, which hinder the absorption of minerals such as zinc, iron, or calcium. ²

Rich in flavor, low in additives 

Fermentation releases numerous compounds that radically transform the organoleptic qualities of fermented foods in terms of: ³ 

• Flavor: the conversion of sugars into organic acids (lactic, acetic, and propionic acids) alters the aromatic profile of foods. For example, propionic acid gives Swiss cheeses (Gruyère, etc.) their characteristic flavor. The fermentation of citrate by certain lactic acid bacteria imparts nutty and buttery hints to products like cottage cheese or Gouda. 
• Smell: fermentation releases unique aromatic compounds (esters, alcohols) that give cheeses, breads, and wine their characteristic smells. 
• Texture and appearance: fermentation can alter physical structure, making yogurt creamy, bread fluffy, and Emmental full of holes thanks to the release of CO2. 

Lastly, fermentation is the art of preservation... without preservatives.
It requires little heavy equipment, eliminates the need for additives (since the acids or alcohol produced by microorganisms keep pathogens at bay), and allows food to be stored at room temperature, avoiding the energy consumption needed for months of refrigeration.  

In sum, there’s no shortage of reasons to put fermented foods on the menu!