RECONSTRUCTION OF HUMAN DIET FROM DELTA-C-13 AND DELTA-N-15 IN CONTEMPORARY JAPANESE HAIR - A STOCHASTIC METHOD FOR ESTIMATING MULTISOURCE CONTRIBUTION BY DOUBLE ISOTOPIC TRACERS

A stochastic method has been proposed for estimating contributions of multi-sources based on a simultaneous measurement of C and N stable isotope compositions of a mixture. Double isotope tracer analyses essentially allow a determination of the mixing proportion of up to three sources by mass balance calculations. For more than three sources, a stochastic approach may provide a possible range of mixing proportions. In this work, a stochastic method using the Monte Carlo simulation was employed for reconstructing the dietary consumption of contemporary Japanese. The mean delta-C-13 and delta-N-15 values of contemporary Japanese scalp hair were found to be -18.2 +/- 0.4 and 10.3 +/- 0.4 parts per thousand relative to PDB and the atmospheric N2, respectively. A dietary model was constructed by using mean isotope ratios of five major food groups and hair for modern Japanese. Based on this model, a stochastic method was applied to simulate human feeding. A range of dietary patterns, consistent with reasonable energy/protein uptake ratio, was estimated for fitting C and N isotope distributions of hair. The estimated mean dietary pattern has protein contributions of 35, 9, 16, 14, 27% from C3 plants, legumes, C4 plants, land animal products, and fish products, respectively, in good agreement with the observed food consumption in the National Statistics Report. The contribution of C4 type plant was estimated to range from 10 to 20% in protein, indicating much higher consumption than the statistical estimation. Thus, this stochastic method is useful in dietary analysis based on C and N isotope ratios. If the isotopic compositions of source materials are sufficiently different and each source is not isotopically reproducible by mixing of others, the stochastic simulation may indicate accurately the different source contributions. This method is applicable also to many geochemical problems where mixing occurs.