Can stable isotope analysis reveal dietary differences among groups with distinct income levels in the city of Piracicaba (southeast region, Brazil)?

BackgroundThe present study aimed to determine whether the C-13 and N-15 of fingernails (C-13(F) and N-15(F), respectively) would exhibit differences between groups from different income levels in the city of Piracicaba, Brazil. MethodsIn 2010, the fingernails of 273 participants belonging to six income groups were analysed to determine isotopic composition. C-13(F) and N-15(F) were compared with the stable isotope of a putative diet (C-13(D) and N-15(D), respectively), which was estimated via an isotopic mass balance using, as a weighting factor, macronutrient intake by the main food items, as obtained by the 2008-2009 household food purchases conducted by the Brazilian Institute of Geography and Statistics. Results(13)C(F) values showed a decreasing trend towards the lower income level groups, in accordance with the C-13(D) values that showed the same trend. This isotopic change was mainly a result of the higher consumption of beef, bread, soft drinks and dairy by the highest income group; and also as a result of the higher consumption of soybean oil, rice and sugar by the lowest income group. The N-15(F) values failed to capture differences in groups between income levels. This outcome was not expected because individuals in a higher income group tend to consume more animal protein and, as a result of the trophic fractionation, have higher N-15 values. ConclusionsThe combination of household purchase surveys and stable isotopic composition in modern humans is found to be a valuable tool, especially with respect to determining the role of C-3 and C-4 plants through the complex modern food chain.