The environmental legitimacy of using and producing secondary resources and products, such as in a circular economy, is based on the assumption that these practices displace the production and consumption of new products. Given how crucial this assumption is for the environmental legitimacy of recycling, reuse, and sharing, the empirical basis remains remarkably uncertain. To improve our understanding of when, where, and how secondary use and production conserves natural resources by displacing the linear economy, a systematic review of previous literature was conducted. In total, 247 studies were identified that examine how recycling, reuse and sharing affect conventional production and consumption systems. The findings reveal that 55% of the studies report positive resource conservation effects, 19% indicate negative effects, 1% no effect, and 25% show mixed results. Hence, in most cases, secondary use led to resource savings. High displacement is observed in cases where isolated raw materials with low contamination sensitivity and high market value are recycled in business-to-business settings. In contrast, low displacement is found when cheap products are reused or shared among consumers. The results show that the displacement is rarely a perfect one-to-one substitution. Instead, the reported levels of displacement and resource savings are often limited, below 50%. Empirically documented cases where acts of circulation have demonstrably trickled down and reduced or postponed natural resource extraction remain absent. The review identifies major gaps in the literature, including a lack of standardized methods for estimating displacement, historical and qualitative analyses, and studies in low-income regions.