How can you convince people to eat more natto -- one of the most controversial foods in the Japanese culinary palette? Try hiding it in a sweet circular cake.

Yamanashi-based natto producer Sendaiya has injected the notoriously stinky fermented soybeans with some universal appeal by injecting them into its new line of natto doughnuts. 

"We wanted to find a way for people who dislike natto to enjoy it," says manager Satoshi Nagatsuka. "We’d heard of tofu doughnuts and thought it might be a good idea to do the same thing with natto." 

The baked treats are marketed as a healthy alternative to regular doughnuts, and the response so far has been pretty good. Sendaiya’s Tokyo branch in Ikejiri-Ohashi (Ryuseido Building 1F, Ikejiri 3-20-3, Setagaya-ku, tel. 03 5431 3935, 10:30-9pm, closed Wednesdays) sells around 100 a day, while the Yamanashi branch sees daily sales of over 400.

The doughnuts are surprisingly tasty, and it's hard to believe they actually contain natto. The soybeans are first dried, then ground to a powder and mixed in with the batter so the natto flavor is barely detectable. 

Mildly sweet, with a moist, cake-like consistency, the natto doughnuts come flecked with black sesame seeds, studded with walnuts, plain or glazed with chocolate. Plain is the most popular, but Nagatsuka recommends the nutty kinako-dusted version for wary first-timers.