Previous research indicates that the Nanchoc Valley in northern Peru was an important locus of early and middle Holocene human settlement, and that between 9200 and 5500 (14)C yr B.P. the valley inhabitants adopted major crop plants such as squash (Cucurbita moschata), peanuts (Arachis sp.), and cotton (Gossypium barbadense). We report here an examination of starch grains preserved in the calculus of human teeth from these sites that provides direct evidence for the early consumption of cultivated squash and peanuts along with two other major food plants not previously detected. Starch from the seeds of Phaseolus and Inga feuillei, the flesh of Cucurbita moschata fruits, and the nuts of Arachis was routinely present on numerous teeth that date to between 8210 and 6970 (14)C yr B.P. Early plant diets appear to have been diverse and stable through time and were rich in cultivated foods typical of later Andean agriculture. Our data provide early archaeological evidence for Phaseolus beans and I. feuillei, an important tree crop, and indicate that effective food production systems that contributed significant dietary inputs were present in the Nanchoc region by 8000 (14)C yr B.P. Starch grain studies of dental remains document plants and edible parts of them not normally preserved in archaeological records and can assume primary roles as direct indicators of ancient human diets and agriculture.