An animal study found that mice fed a walnut-rich diet showed a reduction in lipid peroxidation, a process that can damage sperm cells. This form of cell damage harms sperm membranes, which are primarily made up of polyunsaturated fatty acids (PUFAs).1 Previous studies have shown that PUFAs may play a role in sperm health and membrane function. Walnuts are the only tree nut that are predominantly comprised of PUFAs (one ounce contains 13 grams of PUFAs out of 18 grams of total fat), which is why they were included in this study.
In this study, healthy male mice as well as mice that were genetically predetermined to be infertile (Pmca4-/- gene deletion) were randomly assigned to a walnut-enriched diet containing 19.6% of calories from walnuts (equivalent to about 2.5 ounces per day in humans) or a control diet without walnuts that was followed for 9-11 weeks. Among the mice that consumed walnuts, healthy mice experienced positive shifts in sperm quality factors, including motility (movement) and morphology (form), and the infertile mice showed improvements in sperm morphology. Sperm quality is an indicator of male fertility.2 Additionally, both groups experienced a significant reduction in peroxidative damage. However, investigators were unable to reverse the adverse effects on sperm motility in the infertile mice because of the genetic deletion in this group. This promising animal research provides important insight, but the results are inconclusive regarding the effects on humans and how PUFAs function to reduce lipid peroxidation. Future human clinical studies are needed.
The findings from this study support results from a published randomized control trial in healthy young men (ages 21-35) who ate 75 grams of walnuts per day (about 2.5 ounces). Those who added walnuts to their diet experienced positive shifts in sperm quality factors, including vitality, motility and morphology compared to men who did not add walnuts.3 The participants (117 total subjects) consumed their usual Western-style diet throughout the study and participated in monthly calls to share their dietary intake with the researchers.
This research, led by Wendie A. Robbins, PhD, RN, FAAN of the UCLA Fielding School of Public Health and School of Nursing, suggested a potential role of walnuts in male reproductive health. Intrigued by these findings published in 2012 in Biology of Reproduction, Patricia A. Martin-DeLeon, PhD of the University of Delaware set out to explore possible reasons for the results seen in the study of healthy young men. Although consuming walnuts may have contributed to shifts in certain sperm quality factors in these healthy young men, more research is needed to understand how these findings impact the broader male population, including men in fertility clinics. Together, these studies provide encouraging results regarding male reproductive health research and walnuts may play a role.
1Coffua LS, Martin-DeLeon PA. Effectiveness of a walnuts-enriched diet on murine sperm: involvement of reduced peroxidative damage. Heliyon. 2017;3(2).
2World Health Organization. Laboratory Manual for the Examination and Processing of Human Semen, 5th ed. Cambridge, UK: Cambridge University Press; 2010.
3Robbins WA, Xun L, FitzGerald LZ, et al. Walnuts improve semen quality in men consuming a Western-style diet: randomized control dietary intervention trial. Biol Reprod. 2012;87(4):101.