Insular lizards usually consume a large proportion of plant material compared to mainland ones, which is frequently attributed to a low prey availability on islands. In the present study, we analyze the diets of six populations (three insular and three continental) of the omnivorous lizard Tropidurus torquatus on the eastern Brazilian coast, to assess the extent which the insular and continental lizards differ in feeding habits, especially in the consumption of plant material. The degree of plant consumption varied greatly among areas, with the volumetric proportion of plant food in lizard diets ranging from 5% to 67%, but there was no tendency for insular lizards to consume more plant food than mainland ones. Moreover, insular lizards tended to eat more and larger prey items than those of the mainland, and estimated prey availability was not reduced on the islands compared to the mainland. The results of this study suggest that plant ingestion by T. torquatus is not related directly to insularity, but may be related to prey availability in the habitat. Therefore, the idea that populations of omnivorous lizards invariably tend to consume more plant food on islands than on the mainland must consider whether animal food is limited on a particular island.