Dietary practice during the transition from Early Intermediate Period (200 BC-AD 600) to the Middle Horizon (AD 600-1000) is crucial to understanding Pre-Hispanic life on the southern coast of Peru. The Cerro Del Oro material was excavated in 1925 by Alfred Kroeber and since been biochemically unstudied for almost ninety years; left dormant at The Field Museum in Chicago. Through bioarchaeological reconstruction of diet and health at the site of Cerro Del Oro from a cemetery sample (N=35) in the Cañete Valley, the effects of demographic and subsistence changes can be examined through a combined analysis of osteological and light isotopic data. Stable carbon (¹³C/¹²C, or δ¹³C) and oxygen (¹⁸O/¹⁶O, or δ¹⁸O) isotopic values from tooth enamel carbonate are utilized to reconstruct diet during early childhood of each individual. Results indicate that the majority of the population were consuming a moderately variable terrestrial protein or C₃ diet. This is significant due to the close proximity to marine resources.