Dietary protein content and tissue type control 13 C discrimination in mammals: an analytical approach.

Abstract

RationaleCarbon isotope measurements on collagen and other tissues are used in modern and paleodiet studies, and relating these patterns to the dietary protein fraction (fdp) and to δ13C values of dietary protein and energy (lipids and carbohydrates) remains important for determining diets.MethodsCarbon fluxes from dietary protein to tissues in feeding studies of mice, rats, and pigs were estimated to test how tissue δ13C values related to the δ13C values of dietary protein, dietary energy, fdp, or loge fdp. Values of fdp, protein δ13C, and energy δ13C were used in stepwise regressions that estimated the metabolic routing of dietary protein and the 13C enrichment of tissues relative to dietary protein.ResultsThe 13C enrichment of rat collagen and mouse muscle relative to dietary protein depended on loge fdp and the 13C enrichment of dietary protein on energy: urn:x-wiley:09514198:media:rcm7830:rcm7830-math-0001 The collagen (fcp) or muscle (fmp) fractions derived from dietary protein were estimated as: urn:x-wiley:09514198:media:rcm7830:rcm7830-math-0002 The coefficients of loge fdp reflected the higher proportion of non‐essential amino acids in collagen (79%) than in muscle (61%). In rats, dietary protein contributed from 66% (liver) to 85% (hair) whereas, in mice, dietary protein contributed from 76% (liver) to 85% (body protein). In pigs, collagen derived primarily (83 ± 5%) from dietary protein.ConclusionsThese equations provided analytical frameworks to interpret dietary patterns from isotopic measurements. Metabolic routing and 13C enrichment varied with fdp and with the tissue amino acid composition. Thus, fdp and tissue amino acid compositions were key parameters to assess dietary sources from isotopic values. Incorporating these insights will improve our ability to interpret the isotopic paleorecord and modern diet studies. Copyright © 2017 John Wiley & Sons, Ltd.