Objectives The diet and subsistence in Iron‐Age Öland is debated as earlier studies and different archaeological sources seemingly provide conflicting interpretations. The objectives of this study are therefore to: (i) add new insights on diet and (ii) investigate the chronological variation in detail. It is common in studies of diet to investigate differences between datasets defined by archaeological periods (determined by artefact typology), but it is rare to explore whether these dietary changes are, in fact, well correlated with these temporal categories or not. Materials and methods Stable isotope analysis of 108 individuals and 25 animals was used to interpret diet in comparison with data from earlier studies. Different values of TLE (Trophic Level Effect) for δ15N were compared for interpretations of diet. Of the 108 individuals, 42 were subjected to 14C analysis in this study. Results The isotopes from Iron‐Age animals on Öland indicate that the local, contemporary ecology is specific. The human isotope values show chronological development both when pooled in chronological groups by typology and by more specific 14C chronology. Discussion The new samples of animals as well as the use of 5‰ TLE for δ15N values results in the diet reinterpreted as mainly domesticate‐based, with at least two shifts in diet occurring in the Iron Age. The use of 14C dates in connection with the stable isotope results indicates a dietary transition occurring between 200 BC and AD 200, a date range that spans two typologically determined time periods.