The study brings new insights into how variation in food availability at distinct life stages affects reproductive traits in red flour beetle males and females. We show that both juvenile and adult nutrition interact in shaping female fecundity, whereas male mating activity is influenced primarily by the former. Furthermore, using a powerful statistical approach of path analysis the study investigates the mechanisms behind these effects – specifically, whether the nutrition impact on reproductive traits is mediated by body mass. Surprisingly, we found no mass-mediated effects. This suggests that there must be other mechanisms through which nutrition influences reproduction.