Characteristics

• Sold refrigerated or frozen, natto typically comes in shallow, single-serving polystyrene boxes along with small packets of seasonings such as hot mustard, wasabi, shiso or soy sauce. Two or three boxes are packaged together. The natto itself is a sticky, slimy mass of whole, sliced or coarsely ground soybeans. Fine, sticky threads form when the beans are pulled apart. Stirring the natto makes the slimy matrix turn foamy. Like many fermented foods, natto has a complex flavor.

Making Natto

• In centuries past, natto was made by packing steamed soybeans in straw and leaving them somewhere warm to ferment. Modern natto production begins with washing, soaking and steaming the natto soybeans, then combining them with a mixture of salt, sugar, yeast and a hay bacteria called Bacillus subtilis natto. After a day of fermentation in a warm environment, a cooling period and a week of aging, the natto is ready for the market.

Eating Natto

• While many eat it straight from the box, natto is most often served with rice. A popular breakfast in Japan is natto over rice with a garnish of thinly sliced green onion, sometimes with a raw egg added. Natto is also served over pasta, in sushi rolls, in rice balls, in miso soup and as an ingredient in the grilled Japanese dish okonomiyaki.

Health Benefits

• Natto is a low-cholesterol, easily digested protein. It promotes the growth of beneficial intestinal microflora and is an excellent dietary source of vitamin K2, which plays a critical role in healthy blood clotting and bone mineralization. It is also rich in isoflavones, although the Linus Pauling Institute's Micronutrient Information Center notes that the hypothesized roles these phytoestrogens play in fighting cancer, osteoporosis, menopausal symptoms and heart disease have not been scientifically established. Most famously, natto is the sole source of nattokinase, an enzyme that is widely marketed as a natural dietary supplement. According to Hsu et al. (2009), nattokinase shows potential not only as a clot-dissolving agent for treating heart disease but also a plaque-degrading agent for combating Alzheimer's disease.

The Natto Craze of 2007

• In January 2007, the Japanese television show "Hakkutsu! Aru Aru Daijiten II" touted natto as a scientifically proven rapid weight loss aid. Other media picked up the story, and a nationwide run on natto followed. The natto dieting craze came to an abrupt halt two weeks later, when broadcasting company Kansai Telecasting (KTV) announced that the program had fabricated the story. KTV issued a public apology and subsequently canceled the show.