UCLA researchers are crediting the walnut for its rich source of ALA.
Researchers from the University of California Los Angeles are exploring whether walnuts may promote sperm health and, ultimately, male fertility.
In a dietary intervention trial, 117 young men aged 21 to 35 were assigned to eat 75 g of whole-shelled walnuts daily for 12 weeks or continue with their normal diet while avoiding tree nuts. Each subject was reported as having routinely consumed a Western-style diet.
Compared to baseline, several semen parameters improved after walnut consumption, including sperm vitality, sperm motility (the ability of sperm to reach an egg), and sperm morphology (size and shape). The UCLA researchers believe these changes are likely attributed to walnut's high source of the omega-3 fatty acid ALA and other key nutrients, including folate.
Previous studies have already drawn a connection between fatty acids and sperm health. Higher trans-fat intake has been linked to lower sperm concentrations and omega-3 intake has been linked to normal sperm morphology. One study on both infertile and fertile men found higher omega-6 to omega-3 ratios in infertile men.
But in the case of the walnut study, the researchers presume that improvements in sperm may be more closely tied to one specific omega-3:
In our study, the walnut dietary intervention resulted in a changed serum fatty acid profile for ALA, but not EPA and DHA, suggesting the beneficial omega-3 effects on sperm from walnuts were related to the plant source of omega-3, ALA.
More research is required to assess whether these kinds of sperm improvements could translate to better birth outcomes for infertile men.