The Short Version
Peer-reviewed randomized controlled trials consistently show that walnut consumption produces statistically significant improvements in measurable sperm parameters including motility, vitality, and morphology. The evidence firmly supports the claim as stated — about sperm quality, not fertility outcomes. However, no large-scale study has confirmed these improvements translate to higher pregnancy or live-birth rates, and the primary RCT studied men on a Western-style diet, limiting generalizability.