Extending the limits of paleodietary studies of humans with compound specific carbon isotope analysis of amino acids

Abstract

Stable carbon isotopes in the bone collagen of prehistoric humans are valuable tools for determining human diet. We studied carbon isotopes in individual amino acids (IAA) in plants and collagen from herbivores and humans from North American prehistoric sites in order to determine whether more specific dietary information about Indians could be predicted. The δ 13C of plant amino acids ranged extensively, whereas δ 13C values of each amino acid from the C 3( n=3) and C 4( n=3) plant species were linearly related with a slope of 0.8. Essential amino acids from herbivores had δ 13C values that were completely different from those measured in either C 3or C 4plants, suggesting metabolic resynthesis in the gut by microflora. The δ 13C of essential amino acids from prehistoric North Americans, who had diets ranging from primarily maize-based (C 4) to hunter-gathers (C 3) subsistence, were highly correlated with δ 13C values of herbivore essential amino acids. There was no significant correlation of δ 13C in IAA from humans with those of plants. The δ 13C of nonessential amino acids in human bone collagen can distinguish the presence of maize in the diet, whereas the δ 13C of essential amino acids were transparent to a maize-derived carbon signal. Compound specific isotopic data on IAA distinguish between total carbon intake versus total protein intake and are useful for discerning the extent and nature of omnivory.