Natto is a traditional Japanese food made from soybeans fermented with Bacillus subtilis. It is popular especially as a breakfast food. As a rich source of protein, natto and the soybean paste miso formed a vital source of nutrition in feudal Japan. Natto can be an acquired taste because of its powerful smell, strong flavor, and slippery texture. In Japan natto is most popular in the eastern regions, including Kanto, Tohoku, and Hokkaido.