A. Judith C. Thalheimer, RD, LDN, managing editor of Tufts Health & Nutrition Letter answers: “There is not enough information to know conclusively if eating natto, a popular Japanese dish of soybeans fermented with Bacillus subtilis, can help prevent blood clots. Natto contains an enzyme (called nattokinase) that is very good at dissolving blood clots in laboratory studies. One study found this enzyme to be effective at dissolving blood clots in rats. There is some limited data that nattokinase supplementation in humans enhances markers of anticoagulation, but this is not definitive, and the amounts administered were higher than one would get by simply eating natto.
“Natto has an unusual smell, texture, and taste some people find objectionable. If you enjoy this traditional soy food, it can be a healthy addition to your dietary pattern, but it should not replace medications to prevent blood clots. To be on the safe side, if you are on anticoagulants you should inform your doctor if you eat natto regularly.”