Nuka-daki is Kokura's local fish dish, made by simmering mackerel, sardines or other fish with nuka-doko, a fermented rice-bran bed. Kitakyushu City's report analyzed aged nuka-doko and mackerel nuka-daki from Ajidokoro Yano, including vitamin B1, vitamin B6, magnesium and free GABA.
Look at the sauce as well as the fish
The report measured the fish and the simmering sauce separately. Because many diners enjoy a little sauce with rice, the dish is best understood by considering both the fish and the sauce rather than the fish alone.
Main nutrients identified
Ajidokoro Yano's nuka-daki was found to contain vitamin B1, vitamin B6, magnesium and free GABA. These figures should not be read as health-effect claims. They are evidence for understanding what is present in a local dish that has been passed down as food culture.
Where Yano-style fits
Yano-style nuka-doko is made without soy sauce, sake, mirin or white sugar. In the report's classification, it is close to the traditional style, where the nuka-doko itself functions as the seasoning.
Source: Kitakyushu City, Research Report on Rediscovering the Food-Cultural Value of Kitakyushu's Local Dish Nuka-daki (March 2025).