Epidemiological and animal studies have shown that consumption of fermented soy paste miso, despite its high salt content, does not increase blood pressure and can alleviate metabolic disorders such as obesity. Recently, in addition to normal short-chain peptides, isomerized peptides in which the Asp residue at the amino terminus is in the L/D-α/β form, pyroglutamyl peptides, and cyclic dipeptides referred to as diketopiperazines have been found to exist in miso and soy sauce (shoyu). When a water extract of miso was administered to rats, normal peptides did not increase significantly in the small-intestinal lumen or blood, but some modified peptides increased significantly not only in the lumen but also in the blood. Among the pyroglutamyl peptides in miso, pyroGlu-Leu increased the secretion of host antimicrobial peptides (Rattusin) from the ileum, and ameliorated high-fat diet-induced disruption of the gut microbiota and obesity. The modified peptides that were increased in the blood also inhibited angiotensin-converting enzyme 1. These findings suggest that the functions of these highly bioavailable modified peptides are responsible for the beneficial functions of miso.

Vinegar is an indispensable seasoning, used not only as food but also for medical purposes. Black vinegar is a type of amber rice vinegar and can be classified into two types based on the method of manufacture: fermentation outdoors in a jar, or production in large-scale facilities. Kurozu is a form of black vinegar produced in outdoor environments by filling a pottery jar with steamed rice, water, and rice malt. The empirically recognized health benefits of kurozu have been scientifically verified. Kurozu contains abundant nitrogen compounds in comparison with other vinegars, whereas it contains few carbohydrates. Most of the nitrogen compounds in kurozu are amino acids, but it also contains peptides formed by binding of amino acids and amino acid derivatives. Besides acetic acid, it contains trace amounts of organic acids such as lactic acid, which contribute to its unique flavor and taste. Kurozu also contains polyphenols and fatty acids, and it is estimated that trace amounts of these substances are responsible for its functionality. The benefits of Kurozu have been reported to include not only the blood pressure-lowering and fatigue-relief effects of acetic acid, but also antioxidant effects, antitumor effects, and improvements in lipid and carbohydrate metabolism as well as circulatory function.

Fermented milk has been consumed since ancient times not only for its preservation properties and palatability, but also its health benefits, which have gained increasing attention in recent years. Fermentation of milk or dairy products with lactic acid bacteria (LAB) or yeast yields various foods, yogurt being the most common example. A wide variety of LAB are involved in the fermentation process, and certain strains are known to have specific health-promoting benefits, including regulation of intestinal function, immunomodulation, antihypertensive effects, and improvement of sleep quality. These functions are often strain-dependent, requiring individual scientific evaluation. In recent years, plant-based alternatives to dairy milk have also been developed for fermentation, gaining attention as functional fermented foods that cater to vegan and allergy-conscious consumers, while also addressing environmental concerns. This review provides an overview of fermented milk and LAB, emphasizing their functional properties and introducing recent advances in the application of plant-based milk for fermentation.

Natto is a traditional Japanese fermented food made from soybeans, and various health benefits have been attributed to its fermentation-derived metabolites, such as nattokinase and vitamin K₂. Cohort studies conducted in Japan have reported associations between natto consumption and reduced risks of various diseases, such as cardiovascular disease, osteoporosis, and dementia. We have investigated the effects of natto and natto-derived peptides on cognitive function using mouse models exhibiting cognitive decline. This review outlines the compositional changes occurring in natto during fermentation, the physiological functions of the bioactive components, and the findings of research on cognitive function, thereby exploring the potential contribution of natto consumption to health maintenance and disease prevention.