A randomized 12‑week study with 117 healthy men examined whether daily 75 g of walnuts could improve semen quality. Compared with controls, the walnut group showed notable gains in sperm vitality, motility, and normal morphology, alongside higher serum omega‑3 and omega‑6 levels, though sperm fatty acid content did not differ between groups. The prevalence of sex chromosome disomy and sperm missing a sex chromosome also declined in the walnut group. While the exact mechanisms are unclear, researchers suggest walnut polyunsaturated fats may contribute, but they caution that fertility outcomes were not assessed and further work is needed. The study was funded by the California Walnut Commission and published in Biol Reprod in 2012.
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The study randomly assigned 117 men aged 21 to 35 to either a walnut‑supplemented diet (75 g/day of whole‑shelled walnuts) or a control group for 12 weeks, with semen analyses conducted at the end of the intervention.
Sperm vitality rose by 5.5% in the walnut group versus a 0.51% increase in controls, a difference reported as statistically significant (P = .003).
Sperm motility improved by 5.7% in the walnut group compared with a 0.53% rise in controls, reaching statistical significance (P = .009).
Normal sperm morphology increased by 1.1% in the walnut group versus 0.1% in controls (P = .03), signaling a qualitative improvement in sperm form.
Serum levels of omega‑3 and omega‑6 fatty acids rose in the walnut group after 12 weeks (P = .0007 and P = .0004, respectively), though sperm fatty acid composition did not differ between groups.
The prevalence of sex chromosome disomy and sperm missing a sex chromosome decreased in the walnut group (P = .002 and P = .01, respectively), indicating fewer chromosomal abnormalities.
The authors acknowledge that the precise biological mechanisms are unclear and stress that the study did not assess fertility outcomes such as pregnancy rates; further research is needed to determine real‑world reproductive implications.