A recent trial in Spain known as the Fertinuts study involved over a hundred healthy men in their reproductive prime (18-35 years of age), who had their sperm put under the microscope.
All these men ate a usual Western diet. For the study half of these men continued to eat their usual diet (without nuts), and the other half had a couple of handfuls of nuts (60 g) a day. The nut group was shown to have not only more sperm but better-looking sperm (morphology) that had far more vitality and could swim better!
The trial lasted for 14 weeks and showed walnuts, almonds, and hazelnuts produce happy strong good looking and fast-swimming sperm. This of course is in conjunction with a well-balanced diet. Please seek advice from your dietitian before permanently changing your diet in any major way.