A group of researchers in California conducted a randomized control trial to determine if walnuts provided the some of the necessary components for improved sperm production. It was discovered that as little as 75 g of walnuts per day added to a Western style diet improved sperm vitality, motility, and morphology (normal forms). The improved semen quality was associated
with increases in blood serum omega-6 fatty acids and in the plant source of omega-3 (ALA).

In Chinese medicine the walnut is recommended for building kidney qi which in turn would support healthy sperm production. To maximize the benefit from nuts they are best consumed in their raw form after soaking them for 1 hour or in soups. Roasting walnuts over high heat will destroy much of the oils that are of benefit.

To read the full study click here:
https://www.biolreprod.org/content/87/4/101