The use of carbon and nitrogen stable isotope analyses on human and animal bones contributed over the last decades to better comprehending the diet and subsistence strategies of ancient inhabitants of Southern France. Although they represented a part of the alimentation of these past populations, plants were rarely taken into consideration for diet reconstructions based on stable isotope analyses. This could have led to an underestimation of the importance of the vegetal resources in the human past alimentation and to misinterpretations of the data. Indeed, animal bones are usually used to infer the local environmental baseline and plants are considered mainly through a broad range of values coming from modern specimens. However, several studies stressed the impact of the local environment and climate, as well as anthropic practices on the stable isotope ratios of a plant, making it essential to include them in this type of study. As a matter of fact, numerous of these archaeological sites provided archaeobotanical seeds and fruits, sometimes in large quantities, besides human and animal remains. This study aims to shed new light on the previous diet reconstructions by integrating carbon and nitrogen stable isotope analyses done on charred barley, emmer, and millet grains as well as acorns originating from archaeological sites situated in southern France and dated from the Neolithic to the Iron Age period. In order to obtain the best representation of the local environment, the archaeobotanical remains come from the same archaeological site or as close as possible and are dated from the same period as the human bones. First results obtained for Neolithic populations confirmed that some aspects of the alimentation seemed to have been underestimated or not even considered, such as the consumption of wild resources.