Geographical Difference in Sodium and PotassiumConcentrations of Noodle Soups in Japan

Abstract

The concentrations of sodium and potassium in udon (traditional Japanese noodle) soup were assessed to clarify the geographical differences, since, according to annual report of the National Nutrition Survey, Japan, the mean daily salt intake has been high in Tohoku and Kanto chihos or provinces and in prefectures along the Japan Sea. Six hundred and forty noodle (359 kake-udon and 281 zaru-udon) soup samples were collected from udon and/or soba restaurants located in 198 cities or towns in 45 kens (prefectures) except for Hokkaido and Okinawa in Japan. The mean sodium concentrations of kake-udon soup samples was the highest in Shimane, Ishikawa, and Niigata kens, and the lowest in Hyogo, Osaka and Shiga kens. Using the classification by the National Nutrition Survey, the samples from both Kinki I chiho (Kyoto, Osaka and Hyogo kens) and Kinki II chiho (Nara, Wakayama and Shiga kens) had significantly lower sodium con-centration than those from Hokuriku, Chugoku and South Kanto chihos; the samples from Kinki I chiho had significantly lower sodium concentration than those from Tohoku and North Kanto. The mean sodium concentration of kake-udon soup samples from the areas along Seto-naikai (Okayama, Hiroshima, and south Yamaguchi kens) of Chugoku chiho was significantly lower than that from the areas along Japan Sea (Tottori, Shimane, and north Yamaguchi kens). The mean sodium concentration of kake-udon soup samples from West Japan was significantly lower than that from East Japan. The mean sodium concentration of zaru-udon soup samples from Kinki chiho (Kinki I and Kinki II) was significantly lower than that of the samples from the other eight chihos. In contrast, the potassium concentrations of kake- and zaru-udon soup samples showed no significant difference. In short, the mean sodium concentrations of kake-udon soup samples were the lowest in Kinki chiho, the next lowest in areas along the Seto-naikai of Chugoku chiho, Shikoku ana Kyushu chihos, and the highest in Kanto, Hokuriku and Tohoku chihos. The mean sodium concentration of zaru-udon soup was also the lowest in Kinki chiho, with smaller regional differences. A significant positive correlation (r = 0.676) was found between the mean sodium concentration of kake-udon soup samples and that of zaru-udon soup samples from 10 chihos. A significant positive correlation (r = 0.620) was observed between the mean sodium concentration of kake-udon soups and the mean daily salt intake estimated by the National Nutrition Survey in Japan across 11 chihos. It was shown that the habit of seasoning could determine the regional difference of daily salt intake, reflecting the local populations' preference for salty taste.