Preliminary evidence for medieval Polish diet from carbon and nitrogen stable isotopes

In this pilot study, stable carbon and nitrogen isotopes from bone collagen and apatite of skeletons from the 11th and 12th century cemetery in Giecz, Poland are interpreted. Isotope values from a small number of fish and animal bones from the same archaeological site are also examined. The goal of this research is to provide preliminary evidence of diet for a group of medieval Polish peasants, with particular emphasis on sex-based differences in diet. Results of isotope analyses suggest diet of this early medieval population was omnivorous and terrestrial-based. Fish bones sampled exhibit low δ13C ratios, and in half of the cases are significantly enriched in 15N, indicating they are freshwater species. Human bones do not reflect these signatures, suggesting freshwater fish were not a significant source of dietary protein at Giecz. The 13Ccoll from some human bones is enriched beyond what might be expected from an exclusively C3 diet. Associated mammal bones do not exhibit similarly elevated δ13Ccoll ratios, suggesting enrichment among humans is not due to consumption of animals foddered on C4 plants. Two possible sources of 13Ccoll enrichment are marine fish in diet and direct consumption of a C4 plant, such as millet. The δ13C values obtained from bone apatite of a small subset of humans suggest that millet contributes to 13Ccoll enrichment, although at least three individuals may have also consumed small amounts of marine fish. Sex-based differences in δ15N ratios indicate that men consumed relatively more animal products (meat or dairy) than did women. There is also a correlation between δ13Ccoll and δ15N values in skeletons of men that is absent in women. These carbon and nitrogen isotope data are the first reported for any Polish population and contribute to a more complete picture of dietary adaptation and social organization in medieval Europe.