This paper presents the results of isotopic analysis of prehistoric diet in the Arica region. Using delta C-13 and delta N-15 values obtained from human collagen we evaluate changes in dietary patterns from the early agricultural period (Formative 3500-1500 BP) through to Inka occupation (Late period 550-400 BP). In particular, we examine the impact of maize consumption in the area during periods of major social interaction with the political centres of the Andean highlands. Our results show the continuation of broad-spectrum and marine resource use, rather than a shift to maize-reliance during prehistory. In addition, we compare and contrast our data with previously published work from other Andean regions. We demonstrate biogeographical variation in resource use, probably influenced by the political centres of Wari, Tiwanaku and later the Inka Empire. Contrastingly, results from incremental isotopic analysis of dentine collagen from the Arica infant populations indicate that maize was an important resource for infant-weaning, and comprises a more obvious portion of childhood diet than that of adults.