Macronutrient-based model for dietary carbon routing in bone collagen and bioapatite
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ORIGINAL PAPER
Macronutrient-based model for dietary carbon routing in bone collagen and bioapatite Ricardo Fernandes & Marie-Josée Nadeau & Pieter M. Grootes
Received: 7 May 2012 / Accepted: 21 August 2012 / Published online: 12 September 2012 # Springer-Verlag 2012
Abstract Carbon stable isotope ratios (δ13C), measured in human bone collagen (δ13Ccollagen) and bioapatite (δ13Cbioapatite), are commonly used indicators in ancient human diet reconstruction. The underlying assumption is that human tissues broadly reflect the δ13C signal of dietary food sources (δ13Cdiet) plus an isotopic offset. However, interpretation of results may be confounded by the differentiated routing of macronutrients (energy, that is carbohydrates and lipids, and protein) having associated different isotopic signals (δ13Cenergy, δ13Cprotein). Multiple regression analyses were conducted on data from controlled animal feeding experiments compiled by Froehle et al. (J Archaeol Sci 37:2662–2670, 2010). We derived a simple algebraic macronutrient-based model with δ13Cbioapatite 010.1+ δ13Cdiet (‰) and δ13Ccollagen 04.8+0.74 δ13Cprotein +0.26 δ13Cenergy (‰). While the established relationship for δ13Cbioapatite is similar to previously known results, the model also suggests that δ13Ccollagen signal contributions originate from surprisingly consistent proportions of protein and energy macronutrients. Given that feeding experiments explore extreme variations in the proportion of diet macronutrients, the applicability of the proposed model and its predictions were tested in a variety of well-known, wild animal and human, natural contexts. Possible biochemical mechanisms explaining these empirical results are discussed. R. Fernandes : M.-J. Nadeau : P. M. Grootes Leibniz-Laboratory for Radiometric Dating and Isotope Research, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 11-13, 24118 Kiel, Germany R. Fernandes (*) : M.-J. Nadeau : P. M. Grootes Graduate School “Human Development in Landscapes”, Christian-Albrechts-Universität zu Kiel, Leibnizstr. 3, 24118 Kiel, Germany e-mail: [email protected] R. Fernandes e-mail: [email protected]
Keywords Carbon stable isotopes . Dietary routing . Animal feeding experiments . Macronutrients . Bone collagen . Bioapatite
Introduction The carbon isotopic ratios 13C/12C (which are expressed in the delta notation as δ13C0((13C/12Csample − 13C/12Cstandard)/ (13C/12Cstandard)×1,000‰) of bone collagen (δ13Ccollagen) is one of the most commonly used indicators in ancient human diet reconstruction. The underlying principle is that each food source has a relatively restricted δ13C composition and the corresponding value in human collagen reflects this isotopic ratio plus a (largely kinetic) isotopic enrichment; “You are what you eat (plus a few permil)” (DeNiro and Epstein 1976). The use of human δ13Ccollagen values has proven successful in establishing the transition from a predominately C3 to a C4 (maize) plant-based diet (van der Merwe and Vogel 1978), and is often employed to quantify the contribu
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