Soybean and various types of soy products, such as natto, tofu, miso, and soy sauce, have long been consumed in Japan. Soybean, a rich source of plant proteins, contains a relatively high amount of calcium as well as being an important source of isoflavones, a group of substances whose chemical structure is similar to that of estrogen. Natto, fermented soybeans, contains vitamin K, which is involved in the activation of osteocalcin. For bone health and osteoporosis prevention in Japanese, it is thus beneficial to consume adequate amounts of soybean and soy products on a daily basis.