The stable isotope ratios of carbon and nitrogen (δ13C and δ15N) were measured in composite samples of Japanese food and hair. Three hundred eighty-nine foodstuffs were collected in Tokyo and Gunma Prefecture, Japan, in 2020. The foodstuffs were classified into 15 food categories, prepared as usually consumed, and mixed to make 15 composite samples representing each of the food categories. Similarly prepared samples for foodstuffs collected in 2011 and 2015 were also examined. Composite hair samples were collected from a barber shop in Tokyo and a beauty salon in Gunma in 2019. The δ13C and δ15N values of the food and hair composites were measured by elemental analyzer/isotope ratio mass spectrometry after defatting. The δ13C and δ15N values of the food composite varied from composite to composite and according to year of collection. The whole-diet δ13C values were -21.1, -22.0, and -21.5 ‰ for the 2011, 2015, and 2020 samples, respectively; the δ15N values were 5.0, 4.4, and 4.4 ‰, respectively. Diet-hair offset values of δ13C and δ15N were calculated to be 1.9 and 4.3 ‰ for δ13C and δ15N, respectively. These offset values will be important for dietary analysis and nutritional research using hair isotope ratios.
Keywords: Carbon-13; Japan; diet; foodstuffs; hair; market basket; nitrogen-15.