Fermented Foods and Soy

Have your clients asked about the impact of fermented foods on health? Fermentation is a process by which bacteria break down carbohydrates into alcohol or organic acids. As a result, fermented foods have a slightly distinct and acidic smell to them. Examples of fermented foods and beverages include cheese, sauerkraut, kimchi, kefir, yogurt, kombucha, sourdough bread, stinky tofu, tempeh, miso, and natto. Fermented foods are considered probiotics because they can increase levels of certain bacteria in the gut.

Some evidence suggests fermented soy foods increase the levels of gut bacteria that have been shown to be beneficial to some individuals, including Bifidobacterium and Lactobacillus. In addition, soybeans and some soy foods contain poorly absorbed oligosaccharides and/or fiber, both of which are fuel for the good bacteria in the gut and support digestive health. Furthermore, fermentation generates bioactive compounds absent in unfermented foods or beverages that may exert health benefits.¹^,²^,³

Here’s an overview of some fermented soy foods, how they’re made, and their good-for-you bacteria:

Tempeh is made by fermenting whole soybeans (whereas tofu is made from soymilk) resulting in a cake-like product. It is a traditional food in Indonesia and has more fiber than tofu and offers a nutty flavor and chewier texture. To make tempeh, soybeans are soaked and cooked, and then inoculated with a mold (often a Rhizopus strain) to hasten the fermentation process.
Soy sauce is made by soaking soybeans in a mixture of water, wheat, and salt. This mixture is then naturally fermented with Aspergillus sojae and Aspergillus oryzae molds.
Miso is a paste produced from fermented soybeans. It is widely associated with Japanese cuisine, but it likely originated in China. It’s made from soybeans, salt, and koji (also a strain of Aspergillus oryzae) and is used as a seasoning in soups, sauces, or main and side dishes.
Stinky tofu is a fermented tofu that’s a popular street food in Taiwan. Like its name suggests, it has a strong, pungent smell. It’s made by soaking tofu in a milky brine made with fermented milk and vegetables. Fermentation leads to the production of equol, a metabolite of the isoflavone daidzein, which may have potential health benefits.⁴
Natto is a popular breakfast dish in Japan. The fermented soybeans have a sticky and stringy texture and are often served with rice. To make natto, soybeans are fermented with Bacillus Subtillis var. natto bacteria, which produces the enzyme nattokinase. This enzyme exhibits the ability to inhibit blood clots⁵ and may help reduce the risk of mortality from cardiovascular disease.⁶

There is a growing body of research suggesting the microorganisms used in the fermentation process, and the fermentation-associated modifications that occur in the food, contribute to a wide range of health benefits. Be sure to educate your clients about the potential benefits of including fermented soy products in their diet.

References

Dimidi E, Cox SR, Rossi M, Whelan K. Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease. Nutrients. 2019;11(8):1806. doi:https://doi.org/10.3390/nu11081806
do Prado FG, Pagnoncelli MGB, de Melo Pereira GV, Karp SG, Soccol CR. Fermented Soy Products and Their Potential Health Benefits: A Review. Microorganisms. 2022;10(8):1606. doi:https://doi.org/10.3390/microorganisms10081606
Leeuwendaal NK, Stanton C, O’Toole PW, Beresford TP. Fermented Foods, Health and the Gut Microbiome. Nutrients. 2022;14(7):1527. doi:https://doi.org/10.3390/nu14071527
Jou HJ, Tsai PJ, Tu JH, Wu WH. Stinky tofu as a rich source of bioavailable S-equol in Asian diets. Journal of Functional Foods. 2013;5(2):651-659. doi:https://doi.org/10.1016/j.jff.2013.01.006
Urano T, Ihara H, Umemura K, Suzuki Y, Oike M, Akita S, Tsukamoto Y, Suzuki I, Takada A. The profibrinolytic enzyme subtilisin NAT purified from Bacillus subtilis Cleaves and inactivates plasminogen activator inhibitor type 1. J Biol Chem 2001;276:24690-6.
Nagata C, Wada K, Tamura T, Konishi K, Goto Y, Koda S, Kawachi T, Tsuji M, Nakamura K. Dietary soy and natto intake and cardiovascular disease mortality in Japanese adults: the Takayama study. Am J Clin Nutr 2017;105:426-31.