Carbon and nitrogen stable isotope ratios of diet of the Japanese and diet–hair offset values

Abstract

ABSTRACT The stable isotope ratios of carbon and nitrogen (δ 13C and δ 15N) 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 δ 13C and δ 15N values of the food and hair composites were measured by elemental analyzer/isotope ratio mass spectrometry after defatting. The δ 13C and δ 15N values of the food composite varied from composite to composite and according to year of collection. The whole-diet δ 13C values were −21.1, −22.0, and −21.5 ‰ for the 2011, 2015, and 2020 samples, respectively; the δ 15N values were 5.0, 4.4, and 4.4 ‰, respectively. Diet–hair offset values of δ 13C and δ 15N were calculated to be 1.9 and 4.3 ‰ for δ 13C and δ 15N, respectively. These offset values will be important for dietary analysis and nutritional research using hair isotope ratios.