In the now hyper-arid desert of the south coast of Peru, the natural desiccation of human remains provides a rare and unique opportunity for detailed study into the dietary practices of the people that once lived there. My research investigates the changing subsistence strategies of four groups from the lower Ica Valley from the Early Horizon to the Late Intermediate Period. This area witnessed a dynamic history over this 1500-year time frame, including the emergence and collapse of the Nasca, the spread of influence by the highland Wari empire and the local development of the Ica-Chincha trading society. Yet very little is known about the daily life of the individuals who inhabited this area. By reconstructing their diets it has been possible to examine the economic and land use practices they used as well as the ways in which they created and maintained social relationships using food. Mummified human remains (bone, teeth, hair and skin) from the four Pre-Columbian groups - Late Ocucaje (c.100 B.C.-200 A.D.), Late Nasca (c.450-650 A.D.), Wari (c.800-1000 A.D.) and Ica-Chincha (c.1200-1400 A.D.) - have been analysed for stable carbon and nitrogen isotopes. The combination of multiple tissues has allowed analysis at the intra-individual as well as the intra- and inter-group levels creating a detailed and nuanced dietary reconstruction that incorporates dietary information about childhood, adulthood and over a short-term (monthly) period. The analysis of multiple tissues from the mummified remains has allowed a critical evaluation of the isotopic relationship between different tissues from the same individuals as well as their use for reconstructing dietary life histories. A review of all tissue isotopic comparisons including the data from this research shows that the relationships are difficult to constrain. The carbon and nitrogen isotope data show that terrestrial resources, both plant and animal, were the mainstay of the diet in all four periods. Maize was of varying importance over the time frame, with its contribution to the diet increasing over time. Marine resources did not contribute significantly to the diet, despite their abundance in the middens. The strongest case for social differentiation using food is from the Middle Horizon results, which show a high diversity between groups in terms of dietary choice and do not conform to the hypothesis based on the rich botanical data from the valley. From the observations from all four periods the existing theories about the socio-economic structure of the south coast have been critically evaluated in light of this new evidence.