The stable carbon and nitrogen isotope values (δ13C, δ15N) of collagen and the carbon isotope value of structural carbonate in bioapatite were measured in the bones and teeth of Early Classic to Historic period Maya buried at Chau Hiix, Belize. Diet at Chau Hiix comprised a mixture of resources but contained an unusual amount of protein from high trophic levels. There were no differences between the diets of males and females, and there were no consistent changes in diet from birth to age 12. However, children consumed more maize than adults during all time periods. Similarities in general diet and temporal changes at Chau Hiix, Lamanai, and Altun Ha suggest their participation in a regional socioeconomic system. The diets of the highest-status Early Classic individuals at Chau Hiix, Lamanai, and Altun Ha were different from one another and from those of other individuals buried at their respective sites. We suggest that elites created or attempted to create hierarchies of food consumption within sites during the Classic period and that a heterarchy existed among elites from different sites. During the Postclassic period the major protein component of the Chau Hiix diet shifted from terrestrial animal and/or freshwater resources to reef resources, which suggests increased associations with coastal sites. Temporal changes in diet at Chau Hiix closely paralleled changes at Lamanai, but diets at the two sites were distinct during all time periods.