The American Society for Reproductive Medicine has found evidence that infertility affects men and women equally with about one-third of infertility cases being attributed to male factors, and about one-third to factors that affect women.1 Throughout history, food has been linked with human reproductive success, however most of the emphasis has been on the maternal diet and very little focus has been given to the paternal diet.
Find more about the findings below.
A study of healthy young men (ages 21-35), who ate 75 grams (approximately 2.5 ounces) of walnuts per day experienced positive shifts in sperm quality factors, including sperm vitality, motility (movement) and morphology (form).2 Sperm quality is an indicator of male fertility.3 This randomized, parallel two-group dietary intervention trial included 117 participants who routinely ate a Western-style diet. Approximately half were assigned to consume 75 grams of walnuts per day for 12 weeks as part of their usual diet, while the remaining half followed their typical diet but avoided consumption of tree nuts.
Consuming walnuts may have contributed to shifts in certain sperm quality factors in these healthy young men, but more research is needed to understand how these findings impact the broader male population, including men in fertility clinics. This study also reported higher amounts of alpha-linolenic acid (ALA) provided by walnuts correlated with less frequent sperm aneuploidy, or abnormal cell chromosome numbers. Aneuploidy can result in genetic abnormalities such as Down syndrome. Walnuts are the only nut with an excellent source of ALA, the plant-based omega-3 fatty acid (2.5 grams/ounce).
Another study, in an animal model, explored possible mechanistic reasons for the results seen in the clinical trial. Mice fed a walnut-rich diet showed a reduction in a process called lipid peroxidation, a process that can damage sperm cells.4 This form of cell damage harms sperm membranes, which are primarily made up of polyunsaturated fatty acids (PUFAs). 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. 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.
Additional limitations should be considered for the study in healthy young men. Information on dietary intake and diet adherence was limited since participants were free-living and data was self-reported. Additionally, collection of blood specimens for hormone analysis occurred throughout the day, to accommodate busy schedules of the subjects, but participants were asked to return at the same time of day for follow-up appointments to maintain consistency in the data collection.
1 American Society for Reproductive Medicine. (2016). Quick Facts About Infertility. Retrieved from www.reproductivefacts.org
2 Robbins 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.
3 World Health Organization. Laboratory Manual for the Examination and Processing of Human Semen, 5th ed. Cambridge, UK: Cambridge University Press; 2010.
4 Coffua LS, Martin-DeLeon PA. Effectiveness of a walnuts-enriched diet on murine sperm: involvement of reduced peroxidative damage. Heliyon. 2017;3(2).
