Why we avoid it:

It’s stinky, stringy, slimy, and sticky. Kind of like snot. Natto is made by soaking and steaming soybeans, mixed with Bacillus subtilis and aged in a warm spot until fermented. YouTube is full of people gagging on, or gamely choking down, natto as a challenge.

Why we should eat it:

It’s worth trying to acquire a taste for natto. Eating fermented soy is the traditional, healthy way of eating soy, not the unfermented stuff that we find in grocery stores. Things like soy milk, soy cheese, soy burgers and soy ice creams are not traditional and not healthy. Among the many health benefits attributed to natto, the most important may be its vitamin K2 content. Natto is by far the best food source to get this essential nutrient.

Vitamin K was discovered in 1929 and identified as an important factor in blood clotting. There are three types of vitamin K, one being a synthetic variant we should stay away from, one that occurs in green leafy vegetables and one that occurs in meats and fermented food products. The latter is vitamin K2, called menaquinone, which has distinct physiological actions and benefits from the more common vitamin K1 that directs blood clotting. While most of us obtain adequate vitamin K1, some experts estimate that as high as 99% of the U.S. population might be deficient in vitamin K2. Since the vitamin is soluble in fat, those who are on low-fat diets or eating poorly are probably missing out. So are those with digestive issues that would interfere with absorption.

Vitamin K2 is crucial in maintaining bone mineralization and preventing osteoporosis. Research suggests that K2 might also be good for cardiovascular health by preventing and reversing arterial calcification. Other research is looking at K2 as a therapy for rheumatoid arthritis and prostate cancer. A study published by the European Prospective Investigation into Cancer and Nutrition (EPIC) found that increased intake of K2 reduced the risk of prostate cancer by 35%. The authors note that the effect was more pronounced for advanced prostate cancer and that vitamin K1 did not offer any prostate benefits at all. Such studies add to a small but rapidly growing body of knowledge supporting the health benefits of K2 for bone, cardiovascular, skin, brain and prostate health. Get ready to hear a lot more about this noble vitamin. Head to your nearest Japanese restaurant or market and take the natto challenge. And be sure to film yourself trying it for the first time.