Natto, a traditional Japanese food often used in sushi, may be the next soy option for Americans. This fermented soyfood, practically unknown in the United States, is created when the bacteria Bacillus natto is added to lightly cooked soybeans. The result: Natto has five times the amount of genistein (the isoflavone thought responsible for soy's anticancer benefits) than either tofu or soy milk.
Food and Chemical Toxicology, 1996, vol. 34