While fermented foods have a long history of safe use, there is a growing popular consensus that consumption of fermented foods results in positive health effects. Much of this is driven by popular observations that fermented foods in general use unprocessed raw ingredients, contain little or no added preservatives, colors or flavorings, and are made using long-established, sustainable, and in many cases traditional technologies. Consumers may be attracted to the concept that these are “live foods” containing natural and diverse microbiota.

Human Dietary Studies

A number of controlled human dietary studies have recently been undertaken that sustain the popular perceptions of the health benefits of consuming fermented foods.¹ These studies include investigations that revealed strong associations between weight management and consumption of fermented dairy products;² reduced risk of cardiovascular disease, Type 2 diabetes, and mortality associated with consumption of yogurt;^3–6 and enhanced glucose metabolism and reduced muscle soreness following acute resistance exercise as a consequence of consuming fermented milk.⁷ Consumption of kimchi was linked to antidiabetic and antiobesity effects,^8,9 while consumption of different fermented foods was associated with alterations in mood and brain activity^10–12 and in the gut microbiome.¹³ However, reports have identified a lack of sufficient clinical trials, variation in the different fermented foods being investigated, and inconsistencies among ethnic groups, suggesting that more studies need to be undertaken to confirm the potential benefits of fermented food consumption.¹⁴

Transformations in Food Arising from Fermentation

It well established that fermentation can enhance the digestibility of complex carbohydrates and proteins through the breakdown of starch to oligosaccharides and polypeptides to amino acids^.15,16 Fermentation allows for the destabilization of the casein micelle by bacteria present in milk, enhancing milk protein digestibility.^17,18 Fermentation, in particular with respect to cheese, facilitates the concentration of key nutrients through removal of water and enhances the bioavailability of calcium, which is important for skeletal health.¹⁹ Additionally, fermentation can facilitate transformations in raw foods that allow these foods to be tolerated by individuals who are intolerant of the original raw product. A good example of this is the ability of lactose-intolerant individuals to consume fermented dairy products, in particular ripened cheeses such as cheddar. The reason for this is that during fermentation and cheese ripening, the lactic acid bacteria (LAB) metabolize the lactose, significantly reducing the level of lactose in the resulting fermented food product. In addition, the presence of the lactase enzyme produced by bacteria present in the fermented matrix can help to further remove any residual lactose during ingestion and digestion.²⁰ A similar example involves decrease in the concentration of antinutritional components in raw food, such as the partial eradication of harmful trypsin inhibitors during soy bean fermentation.²¹

In addition, bioactive compounds can be produced through protein, lipid, and carbohydrate catabolism during the fermentation process, and can result from the range of microbial metabolites produced during the process.²² Indeed, production of vitamins and antioxidants during food fermentation has been reported for many LAB species, in particular members of the newly-rebranded Lactobacillaceae family.^23–26 Bioactivities linked to lowering of blood pressure and cholesterol, improvement in metabolic syndromes, anticancer effects, and improvement in immune function have all been described.²⁴ Vitamins B7, B11, and B12 are produced in fermented dairy products by Lactobacillaceae (e.g., Lactiplantibacillus plantarum, Lactobacillus delbrueckii, Limosilactobacillus reuteri), Propionibacterium, Bifidobacterium, and several species of Streptococcus.²⁷ Folic acid (B11) is necessary for development and reproduction and prevents against certain disorders, including some cancers and cardiovascular diseases, while many metabolic processes require B12 as a cofactor, including nucleic and amino acid metabolism.²⁸ Non-dairy fermented foods contain microbes that synthesize vitamins.²⁹

Shalgam is a Turkish fermented beverage consisting of black carrots and turnips; its resident microbiota consists predominantly of Lactobacillaceae, along with Leuconostoc and Pediococcus.³⁰ This beverage is an abundant source of vitamins A, B, and C, as well as other minerals and polyphenols.^29,30 Antioxidants exert beneficial functions in food and protect against the damaging effects of free radicals, and are produced in fermented foods by microbial esterases.²³ Kombucha, a fermented sweetened tea, contains many antioxidants with positive effects on health, including antagonistic effects toward progression of neurodegenerative diseases, diabetes, and certain cancers.²⁹ Many other fermented foods have been shown to positively contribute to different aspects of human health, such as kimchi, a fermented cabbage, which is capable of antiatherogenic effects that are triggered by the active compound 3-(4’-hydroxyl-3’,5’-dimethoxyphenyl) propionic acid (HDMPPA).³¹

Production of Exopolysaccharide

Many food fermentation microbes are capable of producing high molecular weight exopolysaccharides (EPS) from simple sugars present in the raw food product. EPS-producing LAB have been found to have a role in immunomodulation, which can be either stimulatory or suppressive, depending on various factors.³² A study was performed on humans with elevated serum cholesterol levels who were fed fermented oat-based products containing an EPS-producing Pediococcus damnosus strain.³³ This study concurrently noted that a statistically significant reduction in total cholesterol was seen in the group who was given the fermented product, along with a significant increase in the relative abundance of fecal Bifidobacterium species (which are beneficial gut microbes) and total fecal bacterial counts.³³ Thus, fermented foods containing EPS can positively influence gut health.

Evidence of Fermented Foods That Modulate the Gut Microbiome

Fermented foods have been shown to have the capacity to modify gut microbiome populations, although it can often be unclear as to how these changes are brought about. While this has been shown in a myriad of different fermented food types, such as fermented milk,^34–36 yogurt,³⁷ camembert,^38,39 kimchi,⁹ sauerkraut,⁴⁰ and fermented raspberry juice,⁴¹ the results cannot be directly compared due to highly variable parameters, including the use of both healthy and disease models and the various methods by which microbes are quantified. Fermented foods may interfere with the gut microbiome through its own microbiome or through the nutrients present in its matrix. Therefore, in an effort to provide objective evidence that clearly demonstrates whether fermented foods can modulate the human gut microbiome, more in-depth and well-defined human feeding studies need to be undertaken. In these studies, the microbiomes of both the fermented food and the human gut need to be established using the most advanced and sensitive tools available in order to permit changes at both the genus and the species level to be determined.

Conclusion

While a number of studies have demonstrated health benefits associated with fermented foods, more such studies are required. The possibility that fermented foods impact the gut microbiome is intriguing, and merits more study and additional efforts to include investigations of the small intestine.

Editor’s note: Please consult with a dietitian, nutritionist, or other qualified healthcare professional to see if incorporating fermented foods into your diet is right for you.

This article was extracted and adapted from: Leeuwendaal NK, Stanton C, O’Toole PW, Beresford TP.  Fermented foods, health and the gut microbiome. Nutrients. 2022;14(7):1527. Copyright © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. (https://creativecommons.org/licenses/by/4.0/). Access full article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9003261/. Minor edits were made to extracted text for grammatical and style consistencies.

Sources

1. Marco ML, Heeney D, Binda S, et al. Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. 2017;44:94–102. 
2. Mozaffarian D, Hao T, Rimm EB, et al. Changes in diet and lifestyle and long-term weight gain in women and men. N Engl J Med. 2011;364:2392–2404. 
3. Chen M, Sun Q, Giovannucci E, et al. Dairy consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. BMC Med. 2014;12:215. 
4. Eussen SJPM, Van Dongen MCJM, Wijckmans N, et al. Consumption of dairy foods in relation to impaired glucose metabolism and type 2 diabetes mellitus: the Maastricht Study. Br J Nutr. 2016;115:1453–1461. 
5. Soedamah-Muthu SS, Masset G, Verberne L, et al. Consumption of dairy products and associations with incident diabetes, CHD and mortality in the Whitehall II study. Br J Nutr. 2013;109:718–726. 
6. Tapsell LC. Fermented dairy food and CVD risk. Br J Nutr. 2015;113:S131–S135. 
7. Iwasa M, Aoi W, Mune K, et al. Fermented milk improves glucose metabolism in exercise-induced muscle damage in young healthy men. Nutr J. 2013;12:83. 
8. An SY, Lee MS, Jeon JY, et al. Beneficial effects of fresh and fermented kimchi in prediabetic individuals. Ann Nutr Metab. 2013;63:111–119. 
9. Han K, Bose S, Wang JH, et al. Contrasting effects of fresh and fermented kimchi consumption on gut microbiota composition and gene expression related to metabolic syndrome in obese Korean women. Mol Nutr Food Res. 2015;59:1004–1008. 
10. Tillisch K, Labus J, Kilpatrick L, et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013;144:1394–1401. 
11. Hilimire MR, DeVylder JE, Forestell CA. Fermented foods, neuroticism, and social anxiety: an interaction model. Psychiatry Res. 2015;228:203–208. 
12. Omagari K, Sakaki M, Tsujimoto Y, et al. Coffee consumption is inversely associated with depressive status in Japanese patients with type 2 diabetes. J Clin Biochem Nutr. 2014;55:135–142. 
13. Taylor BC, Lejzerowicz F, Poirel M, et al. Consumption of fermented foods is associated with systematic differences in the gut microbiome and metabolome. mSystems. 2020;5:901–920. 
14. Sivamaruthi BS, Kesika P, Chaiyasut C. Impact of fermented foods on human cognitive function—a review of outcome of clinical trials. Sci Pharm. 2018;86:22. 
15. Yadav S, Khetarpaul N. Indigenous legume fermentation: effect on some antinutrients and in-vitro digestibility of starch and protein. Food Chem. 1994;50:403–406. 
16. Çabuk B, Nosworthy MG, Stone AK, et al. Effect of fermentation on the protein digestibility and levels of non-nutritive compounds of pea protein concentrate. Food Technol Biotechnol. 2018;56:257–264. 
17. Beermann C, Hartung J. Physiological properties of milk ingredients released by fermentation. Food Funct. 2013;4:185–199. 
18. Jardin J, Mollé D, Piot M, et al. Quantitative proteomic analysis of bacterial enzymes released in cheese during ripening. Int J Food Microbiol. 2012;155:19–28. 
19. Rozenberg S, Body JJ, Bruyere O, et al. Effects of dairy products consumption on health: Benefits and beliefs—a commentary from the Belgian Bone Club and the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases. Calcif Tissue Int. 2015;98:1–17. 
20. Granato D, Branco GF, Nazzaro F, et al. Functional foods and nondairy probiotic food development: Trends, concepts, and products. Compr Rev Food Sci Food Saf. 2010;9:292–302. 
21. Hong K-J, Lee C-H, Kim SW. Aspergillus oryzae GB-107 fermentation improves nutritional quality of food soybeans and feed soybean meals. J Med Food. 2004;7:430–435. 
22. Leroy F, De Vuyst L Fermented food in the context of a healthy diet: how to produce novel functional foods? Curr Opin Clin Nutr Metab Care. 2014;17:574–581. 
23. Kamal-Eldin A. The role of fermentation in providing biologically active compounds for the human organism. In: Metha BM, Kamal-Eldin A, Iwanski RZ, editors. Fermentation: Effects on Food Properties. CRC Press; Boca Raton, FL, USA: 2012;151–168. 
24. Şanlier N, Gökcen BB, Sezgin AC. Health benefits of fermented foods. Crit Rev Food Sci Nutr. 2017;59:506–527. 
25. Samaranayaka AGP, Li-Chan ECY. Food-derived peptidic antioxidants: a review of their production, assessment, and potential applications. J Funct Foods. 2011;3:229–254. 
26. Zheng J, Wittouck S, Salvetti E, et al. A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Int J Syst Evol Microbiol. 2020;70:2782–2858. 
27. Fernández M, Hudson JA, Korpela R, de los Reyes-Gavilán CG. Impact on human health of microorganisms present in fermented dairy products: an overview. BioMed Res Int. 2015;2015:412714. 
28. Stanton C, Ross RP, Fitzgerald GF, Van Sinderen D. Fermented functional foods based on probiotics and their biogenic metabolites. Curr Opin Biotechnol. 2005;16:198–203. 
29. Baschali A, Tsakalidou E, Kyriacou A, et al. Traditional low-alcoholic and non-alcoholic fermented beverages consumed in European countries: a neglected food group. Nutr Res Rev. 2017;30:1–24. 
30. Altay F, Karbancioglu-Güler F, Daskaya-Dikmen C, Heperkan D. A review on traditional Turkish fermented non-alcoholic beverages: microbiota, fermentation process and quality characteristics. Int J Food Microbiol. 2013;167:44–56. 
31. Kim HJ, Noh JS, Song YO. Beneficial effects of kimchi, a Korean fermented vegetable food, on pathophysiological factors related to atherosclerosis. J Med Food. 2017;21:127–137. 
32. Ryan PM, Ross RP, Fitzgerald GF, et al. Sugar-coated: exopolysaccharide producing lactic acid bacteria for food and human health applications. Food Funct. 2015;6:679–693. 
33. Mårtensson O, Biörklund M, Lambo AM, et al. Fermented, ropy, oat-based products reduce cholesterol levels and stimulate the bifidobacteria flora in humans. Nutr Res. 2005;25:429–442. 
34. Veiga P, Pons N, Agrawal A, et al. Changes of the human gut microbiome induced by a fermented milk product. Sci Rep. 2014;4:6328. 
35. Unno T, Choi JH, Hur HG, et al. Changes in human gut microbiota influenced by probiotic fermented milk ingestion. J Dairy Sci. 2015;98:3568–3576. 
36. Yılmaz İ, Enver Dolar M, Özpınar H. Effect of administering kefir on the changes in fecal microbiota and symptoms of inflammatory bowel disease: a randomized controlled trial. Turk J Gastroenterol. 2019;30:242–253. 
37. Lisko D, Johnston G, Johnston C. Effects of dietary yogurt on the healthy human gastrointestinal (GI) microbiome. Microorganisms. 2017;5:6. 
38. Firmesse O, Rabot S, Bermúdez-Humarán LG, et al. Consumption of Camembert cheese stimulates commensal enterococci in healthy human intestinal microbiota. FEMS Microbiol Lett. 2007;276:189–192. 
39. Firmesse O, Alvaro E, Mogenet A, et al. Fate and effects of Camembert cheese micro-organisms in the human colonic microbiota of healthy volunteers after regular Camembert consumption. Int J Food Microbiol. 2008;125:176–181. 
40. Nielsen ES, Garnås E, Jensen KJ, et al. Lacto-fermented sauerkraut improves symptoms in IBS patients independent of product pasteurisation—a pilot study. Food Funct. 2018;9:5323–5335. 
41. Wu T, Chu X, Cheng Y, et al. Modulation of gut microbiota by Lactobacillus casei fermented raspberry juice in vitro and in vivo. Foods. 2021;10:3055.