In response to the urgent global issue of food waste, our research investigates an unexplored dimension: the effect of joint versus individual consumption. Using one field, four experimental studies and a single-paper meta-analysis, our re- search finds that compared to individual consumption, joint consumption results in increased food consumption and subsequent waste. This behavior is driven by a heightened concern about self-presentation and a diffusion of responsibility among group members. Importantly, we observed that when group members in the joint consumption share close relationships, this effect diminishes or even reverses. Furthermore, our study proposes a practical solution for addressing food waste in joint consumption scenarios by implementing intervention messages that highlight individual responsibility.