From field to fish: Tracking changes in diet on entry to two medieval friaries in northern England

Members of religious orders during the later medieval period in Britain were expected to adhere to strict rules governing their daily lives which restricted their consumption of meat. This study aims to investigate whether this switch to a 'religious diet' can be isotopically detected in presumed religious individuals upon their entry into a religious order during adolescence. Secondary aims of this study include: 1) a comparison of the carbon (delta C-13) and nitrogen (delta N-15) stable isotope values between individuals with and without diffuse idiopathic skeletal hyperostosis (DISH); and 2) to compare the mean values of the sites analyzed with geographically and temporally related sites from previously published studies. To achieve these aims, delta C-13 and delta Nd-15 analysis of third molar incremental dentine collagen and bulk rib bone collagen was undertaken on ten presumed religious individuals: five from the Carmelite friary at Priory Close, Northallerton, founded in 1356 CE, and five from the Friars of the Sack-turned-Carmelite friary at Clavering Place, Newcastle-upon-Tyne, founded in 1266 CE. Twelve contemporaneous faunal samples were also analyzed to provide an isotopic baseline. The delta C-13 and delta N-15 profiles of all individuals from both sites in this study increased from the beginning of the formation of the third molar at c. 8.5 years to its completion at c. 23.5 years indicating a shift during adolescence from a largely terrestrial mixed diet to one that contained a significant amount of animal and marine protein. Individuals exhibiting skeletal pathology indicative of DISH were found to have individual delta C-13 and delta N-15 values that were elevated above the means for each site, and the mean rib collagen delta C-13 and delta N-15 values at Priory Close and Clavering Place were in line with published data from other later medieval religious sites in northeastern England. This study provides evidence for a shift in diet experienced by members of religious orders during adolescence and lays the foundation for future studies of dietary changes at different religious institutions.