Abstract: Recommender systems present relevant content to users and help content creators reach their target audience. The dual nature of these systems influences both users and creators: users' preferences are altered by the items they are recommended, while creators are incentivized to alter their content such that it is recommended more frequently.We define a model, called user-creator feature dynamics, to capture the dual influences of recommender systems.We prove that a recommender system with dual influence is guaranteed to polarize, causing diversity loss in the system.We then investigate, both theoretically and empirically, approaches for mitigating polarization and promoting diversity in recommender systems.Unexpectedly, we find that common diversity-promoting approaches do not work in the presence of dual influence, while relevancy-optimizing methods like top-$k$ recommendation can prevent polarization and improve diversity of the system.