This study investigates how paternal diet affects offspring metabolism through sperm maturation and fertilization in mammals. The research shows that dietary conditions influence the levels of small RNAs, including tRNA fragments, in sperm. These tRNA fragments are primarily generated in the epididymis during sperm maturation and are transported to sperm via epididymosomes. The study reveals that tRNA fragments, particularly tRF-Gly-GCC, regulate the expression of genes associated with the endogenous retroelement MERVL, which is active in the preimplantation embryo. These findings highlight the role of small RNA biogenesis during post-testicular sperm maturation and suggest that tRNA fragments can influence the expression of retroelement-driven transcripts. The study also demonstrates that paternal diet can affect preimplantation gene regulation through RNAs in sperm, potentially impacting offspring metabolism. Overall, the research underscores the importance of paternal diet in shaping the sperm epigenome and its impact on offspring development.This study investigates how paternal diet affects offspring metabolism through sperm maturation and fertilization in mammals. The research shows that dietary conditions influence the levels of small RNAs, including tRNA fragments, in sperm. These tRNA fragments are primarily generated in the epididymis during sperm maturation and are transported to sperm via epididymosomes. The study reveals that tRNA fragments, particularly tRF-Gly-GCC, regulate the expression of genes associated with the endogenous retroelement MERVL, which is active in the preimplantation embryo. These findings highlight the role of small RNA biogenesis during post-testicular sperm maturation and suggest that tRNA fragments can influence the expression of retroelement-driven transcripts. The study also demonstrates that paternal diet can affect preimplantation gene regulation through RNAs in sperm, potentially impacting offspring metabolism. Overall, the research underscores the importance of paternal diet in shaping the sperm epigenome and its impact on offspring development.