A study in the US has found that regular consumption of walnuts can improve sperm morphology, motility and vitality. A total of 117 healthy men ranging in age from 21 to 35, were randomly allocated to one of two groups: the intervention group of 59 men consumed 75g of walnuts per day, provided to them in small snack packs; the remaining 58 men adhered to their usual diet, whilst avoiding tree nuts.
Interestingly, these findings correlate with the use of walnuts for centuries in traditional Chinese medicine, to support sexual function and fertility.
(Walnuts Improve Semen Quality in Men Consuming a Western-Style Diet: Randomised Control Dietary Intervention Trial. Biology of Reproduction Journal, October 2012.)