Walnuts: Sperm Quality and Fertility

Table of Contents

1. Why Sperm Depend on Polyunsaturated Fat
2. What a Semen Analysis Measures
3. The 75-Gram Walnut Trial
4. Reading That Trial Carefully
5. The FERTINUTS Mixed-Nut Trial
6. Sperm DNA Methylation: The Follow-Up
7. Erectile and Sexual Function
8. What Observational Studies Show
9. The Pooled Analysis
10. Men With Diagnosed Infertility
11. Animal Studies
12. What Is Not Known
13. Who the Research Raises Cautions For
14. Connections
15. Key Research Papers
16. Featured Videos

Why Sperm Depend on Polyunsaturated Fat

A sperm cell is mostly a packet of DNA with a motor attached. Almost everything that lets it swim and fuse with an egg happens at its outer skin, the cell membrane, and that membrane is built from fats.

Human sperm membranes are unusually rich in polyunsaturated fatty acids — fats whose carbon chains contain several double bonds. Those double bonds make the membrane loose and fluid, which the sperm needs: the tail has to whip thousands of times, and at the end of the journey the head has to change shape and merge its membrane with the egg's. A stiff, saturated membrane would not do that well.

The same double bonds are also the weak point. They are where oxygen attacks. When unstable oxygen molecules — reactive oxygen species, often called free radicals — meet those fats, they set off a chain reaction called lipid peroxidation, in which one damaged fat molecule damages the next. In a review of the field, Aitken described how human sperm both produce reactive oxygen species themselves and are highly susceptible to this peroxidative damage, and why that oxidative stress has been studied as a cause of male infertility. The same review makes a point that is easy to miss: in small, physiological amounts these reactive molecules are part of how normal sperm function is switched on. The issue is excess, not presence.

Sperm are poorly equipped to repair themselves. They have shed most of their cytoplasm, the watery interior that in other cells holds protective enzymes, so they depend heavily on the antioxidants in the fluid around them.

That is the reason walnuts drew attention. Among common nuts they are the outstanding source of alpha-linolenic acid (ALA), the plant form of omega-3 fat (the amounts are set out on the ALA omega-3 page), and they also carry vitamin E in its gamma-tocopherol form, polyphenols and folate. The hypothesis the trials tested was simple: supply the building material for the membrane and some of its protection in one food, and see whether the sperm change.

What a Semen Analysis Measures

Every trial on this page reports semen measurements, so it helps to know what each one means.

• Concentration and total count — how many sperm are present per millilitre, and in the whole sample.
• Vitality — the share of sperm that are alive, usually judged by whether a dye can get through the membrane. A damaged membrane lets the dye in.
• Motility — the share that move; progressive motility is the share that swim forward rather than twitch in place.
• Morphology — the share with a normal shape of head, midpiece and tail under strict laboratory criteria. Even in fertile men most sperm are classed as abnormal by these criteria.
• Aneuploidy — sperm carrying the wrong number of chromosomes (for example a missing or extra sex chromosome). Nullisomy means a chromosome is missing altogether.
• DNA fragmentation — the share of sperm whose DNA is broken.
• DNA methylation — small chemical tags on the DNA that switch genes on or off without changing the genetic code itself.

The essential caution: these are markers, not outcomes. Semen parameters are used in fertility clinics because, on average, they track a couple's chance of conceiving, but they track it loosely. Many men with poor numbers father children without help, and many with normal numbers do not. A trial that improves motility by some percentage points has shown exactly that, and nothing more, until someone counts pregnancies.

The 75-Gram Walnut Trial

Robbins and colleagues at the University of California, Los Angeles published the first randomised trial of walnuts and sperm in Biology of Reproduction in 2012.

• Who: 117 healthy men aged 21 to 35 who routinely ate a Western-style diet. They were not selected for fertility problems.
• Design: randomised, parallel two-group trial. The people assessing the semen samples did not know which group a sample came from (single-blind masking of outcome assessors).
• Intervention: 75 grams of whole shelled walnuts a day — a little over two and a half ounces — added to the usual diet (59 men). The control group (58 men) kept eating their usual diet but avoided tree nuts.
• Duration: 12 weeks.
• Primary outcomes: conventional semen parameters and sperm aneuploidy. Secondary outcomes were blood and sperm fatty-acid profiles, sex hormones and serum folate.

Results as reported in the abstract:

• The walnut group improved in sperm vitality, motility and morphology (normal forms). The control group did not change.
• Comparing the change from baseline between the groups, the differences were statistically significant for vitality (P = 0.003), motility (P = 0.009) and morphology (P = 0.04).
• Blood fatty-acid profiles shifted in the walnut group, with increases in omega-6 (P = 0.0004) and omega-3 (P = 0.0007) fats, and a rise in ALA specifically (P = 0.0001). No such change was seen in the controls.
• Sperm aneuploidy was inversely correlated with the ALA content of the sperm — men whose sperm held more ALA had fewer chromosomally abnormal sperm — most clearly for missing sex chromosomes (Spearman correlation −0.41, P = 0.002).

The authors concluded that walnuts added to a Western-style diet improved sperm vitality, motility and morphology.

Reading That Trial Carefully

Several details matter for what the trial does and does not show.

• The chromosome finding is a correlation, not a group result. The abstract reports an association between sperm ALA and aneuploidy across men; it does not report that the walnut group had significantly fewer chromosomally abnormal sperm than the control group. Summaries that say walnuts "improved chromosomal integrity" go further than the abstract does.
• Concentration and count are not listed among the improvements. The three significant changes were vitality, motility and morphology.
• The men were healthy and young. They were not men attending a fertility clinic, so the trial cannot say whether the same change would occur, or would matter, in men with a diagnosed problem.
• The hormone and folate results are not described in the abstract. They were secondary endpoints; this page does not report them.
• The dose was large. Seventy-five grams is roughly two and a half standard one-ounce servings every day for three months.
• No pregnancies were counted. This was a trial of semen markers.
• Only the outcome assessors were blinded. Participants obviously knew whether they were eating walnuts, which is unavoidable in a whole-food trial.

With 117 men it is a respectable size for a semen study, and its design — randomised, controlled, assessors masked — is better than most of the diet-and-sperm literature, which is overwhelmingly observational.

The FERTINUTS Mixed-Nut Trial

The second trial came from a nutrition group in Reus, Spain, and was published by Salas-Huetos and colleagues in the American Journal of Clinical Nutrition in 2018. It was designed in part to look for the mechanisms behind the Los Angeles result.

• Who: 119 healthy men aged 18 to 35 eating a Western-style diet. Men who already ate nuts often or had a nut allergy were excluded.
• Intervention: 60 grams a day of mixed raw nuts added to the usual diet — according to the trial's methods, 30 grams of walnuts, 15 grams of almonds and 15 grams of hazelnuts, supplied free in pre-weighed monthly packs. The control group kept their usual diet and avoided nuts.
• Duration: 14 weeks.
• Primary outcomes: conventional semen parameters (pH, volume, count, concentration, motility, morphology). Sperm DNA fragmentation, reactive-oxygen-species production, chromosome anomalies for chromosomes X, Y and 18, total DNA methylation and microRNA expression were measured as possible explanations.

Results as reported:

• Compared with the control group, the nut group improved in total sperm count (P = 0.002), vitality (P = 0.003), total motility (P = 0.006), progressive motility (P = 0.036) and morphology (P = 0.008).
• The nut group had a significant reduction in sperm DNA fragmentation (P < 0.001) and in the expression of one microRNA, hsa-miR-34b-3p (P = 0.036). MicroRNAs are short pieces of genetic material that help regulate which genes are active.
• The nut group's diet rose in total fat, monounsaturated and polyunsaturated fat, magnesium, vitamin E, ALA, total omega-3 and the omega-3 to omega-6 ratio.
• No significant differences between groups were found in reactive-oxygen-species production, sperm chromosome anomalies, or total DNA methylation.

Two things stand out. First, FERTINUTS reproduced the vitality, motility and morphology findings with a smaller walnut dose inside a mixture, and added an improvement in total count that the walnut-only trial had not reported. Second, it did not reproduce any effect on chromosome anomalies, and it did not find the drop in reactive oxygen species that the oxidative-stress explanation would predict — the authors suggested the changes could be partly explained by the reduction in DNA fragmentation instead.

Because the intervention was a mixture, FERTINUTS cannot separate what walnuts contributed from what almonds and hazelnuts contributed.

Funding as stated: the FERTINUTS sub-analysis published in Nutrients in 2019 states that the work was partly supported by a grant from a non-profit international nut-industry council and by university funds, and that the nuts were donated by a nut supplier. One author declared an unpaid advisory role with the same council, and another declared research funds from a nut growers' association. Industry funding does not make a result wrong, but readers are entitled to know it.

Sperm DNA Methylation: The Follow-Up

Salas-Huetos and colleagues returned to FERTINUTS samples for a post hoc analysis, published in Andrology in 2021, working with a laboratory in Utah. They randomly selected 72 of the 98 men who had completed the trial (48 from the nut group, 24 controls) and mapped the methylation tags across their sperm DNA at the start and after 14 weeks.

• Global methylation did not change significantly between groups — consistent with the main trial.
• In the nut group, 36 specific regions of the genome changed methylation significantly between baseline and the end of the trial, and 97.2% of them became more methylated. No such change was found in the control group over the same period.
• Using a "germ line age" calculator, which estimates the biological age of sperm cells from their methylation pattern, the researchers found no difference attributable to nut intake.

The authors described the effect as subtle and concluded that some regions of the sperm epigenome appear to respond to diet. What those 36 regions do, and whether the changes matter for fertility or for children conceived, is not known. This was a secondary analysis of a subset, not a trial designed to answer that question.

Erectile and Sexual Function

A further FERTINUTS sub-analysis, published in Nutrients in 2019, looked at erectile and sexual function in 83 of the men (43 nut group, 40 controls) using a standard 15-question questionnaire, the International Index of Erectile Function, together with two blood markers of blood-vessel function, nitric oxide and E-selectin.

• Compared with controls, the nut group reported significant increases in orgasmic function (p = 0.037) and sexual desire (p = 0.040).
• There were no significant differences in nitric oxide or E-selectin, so the blood-vessel explanation was not supported by those markers.

These were healthy young men without erectile dysfunction, the outcomes were self-reported, and participants knew which group they were in. The finding is a secondary outcome, not proof of an effect on erectile dysfunction.

What Observational Studies Show

Observational studies look at what men already eat and compare their semen, without assigning a diet. They can show associations but not cause and effect.

The Led-Fertyl study (2026). Dávila-Córdova and colleagues, from the same Spanish group, analysed 222 healthy young men in a cross-sectional study published in Andrology. Nut intake was grouped as fewer than 3, 3 to fewer than 7, and 7 or more 30-gram servings a week. Men in the highest group had higher total sperm count and concentration than those in the lowest, and each extra daily serving was associated with higher count and concentration. Compared with the lowest group, men in the highest group had lower odds of abnormal motility (odds ratio 0.25) and of any abnormality on the semen analysis (odds ratio 0.31). In a statistical substitution model, swapping a daily serving of nuts for a serving of potato chips or pastries was associated with lower count and concentration. The study did not separate walnuts from other nuts, and because it measured diet and semen at one point in time it cannot show which came first.

The broader diet literature. A 2017 systematic review of 35 observational studies in Human Reproduction Update, by Salas-Huetos and colleagues, found that diets richer in omega-3 fats and in antioxidants such as vitamin E, vitamin C, beta-carotene, selenium, zinc, cryptoxanthin and lycopene, as well as vitamin D and folate, and lower in saturated and trans fats, were associated with better semen quality. Diets heavy in processed meat, sugar-sweetened drinks, sweets and alcohol were associated with poorer semen in some studies. The authors stressed that these associations need confirming in large prospective studies and randomised trials. Walnuts sit naturally in the favourable pattern, but this review is about diet as a whole, not about walnuts.

The Pooled Analysis

Cardoso, Fratezzi and Kellow at Monash University published a systematic review and meta-analysis of nut consumption and fertility in Advances in Nutrition in 2024, covering studies up to June 2023 in which people of reproductive age ate nuts for at least three months.

• Only four studies qualified, with 875 participants (646 men, 229 women).
• Pooling the two randomised trials in 223 healthy men — the walnut trial and FERTINUTS — eating 60 grams or more of nuts a day increased sperm motility, vitality and morphology compared with controls, but had no effect on sperm concentration.
• The non-randomised studies reported no association between nut intake and conventional sperm parameters, and no association with embryo implantation, clinical pregnancy or live birth in men and women undergoing assisted reproduction.

This is the honest summary of the field. The randomised evidence for better semen markers rests on two trials, both in healthy young men on Western diets, at fairly high doses. The only data on pregnancy and birth are observational, come from couples already in fertility treatment, and found nothing.

Men With Diagnosed Infertility

Both nut trials enrolled healthy volunteers. A PubMed search of walnut and sperm records (October 2026) turned up no randomised trial of walnuts in men diagnosed with infertility, and no trial of walnuts in couples trying to conceive.

The nearest evidence is for omega-3 supplements rather than walnuts. A 2019 meta-analysis by Hosseini and colleagues in the Journal of Dietary Supplements pooled three randomised trials in infertile men (147 treated, 143 controls) that gave the marine omega-3 fats EPA and DHA, alone or with other nutrients. Omega-3 treatment significantly increased sperm motility and the DHA content of seminal fluid, but did not change sperm concentration or the DHA content of the sperm themselves, and the results varied a lot between trials. Marine EPA and DHA are not the same as walnut ALA — the body converts only a small part of ALA into those longer fats — so this cannot be read across directly.

Other nutrients studied for male infertility have their own pages on this site, including carnitine and CoQ10.

Animal Studies

The following are animal studies. They help with mechanism but are not evidence of an effect in people.

• Walnut diet in mice (2017). Coffua and Martin-DeLeon fed mice a walnut-enriched diet designed to parallel the human trial, including a strain bred with a genetic defect in sperm motility. In normal mice the diet significantly improved sperm motility and morphology; in the defective strain it improved morphology. Vitality and the acrosome reaction (the change the sperm head undergoes to penetrate an egg) were unaffected. In both strains, sperm lipid peroxidation fell significantly — the most direct evidence so far that walnuts reduce oxidative damage to sperm membranes, though in mice. The diet did not reverse the increased cell death seen in the testes of the defective strain. The authors noted the effect appeared more modest in mice than in men.
• "African walnut" in rats. A 2021 rat study by Ikwuka and colleagues reported that feed containing African walnut partly offset the damage that nicotine did to sperm motility and count. African walnut is a different plant (Tetracarpidium conophorum, also classed as Plukenetia conophora) from the English walnut (Juglans regia) discussed on the rest of this page, so this study says nothing direct about walnuts as most readers know them. The paper's own suggestion that it be used as a supplement for infertile men goes well beyond what a rat study can show.
• Several other rat studies have given walnut oil to animals exposed to testicular toxins such as lead or nitrite and reported less damage; these are listed under the PubMed topic searches below.

Historical note. Walnuts appear among the foods that the Persian physician Avicenna (Ibn Sina) listed in his Canon of Medicine for improving semen and male fertility, alongside almonds, pistachios, hazelnuts, sesame, dates and others. A 2021 review by Sadogh and colleagues traced those foods into modern studies; it is a narrative review that found the evidence encouraging but called for further studies.

What Is Not Known

• Whether walnuts increase pregnancies or live births. No randomised trial has measured either. The only data on those outcomes, pooled in the 2024 meta-analysis, are observational, from couples in fertility treatment, and showed no association.
• Whether the effect holds in men with infertility. Both trials studied healthy young volunteers.
• What dose is needed. The trials used 75 grams of walnuts, and 60 grams of mixed nuts containing 30 grams of walnuts. No trial has compared doses, and no trial has tested a typical single one-ounce serving.
• How long the changes last once nut eating stops, and whether they continue to build beyond three months.
• Which component is responsible. ALA, vitamin E, polyphenols, folate, magnesium and the simple replacement of other snack foods are all candidates. The mouse study points to reduced lipid peroxidation; FERTINUTS points to less DNA fragmentation but found no change in reactive oxygen species.
• Whether the chromosome signal is real. The walnut trial found a correlation between sperm ALA and aneuploidy; FERTINUTS found no group difference in chromosome anomalies.
• What the methylation changes mean. The 36 altered regions have not been linked to any fertility or offspring outcome.
• Independent replication. Apart from the Los Angeles trial, the human studies come largely from one research group in Spain.

Who the Research Raises Cautions For

• People with a tree-nut allergy. Walnuts are a common tree-nut allergen; FERTINUTS excluded men with a known nut allergy.
• Calorie load. The trial amounts are substantial. Seventy-five grams of walnuts a day is about two and a half one-ounce servings, and walnuts are energy-dense. The abstracts of the two trials do not report body-weight results.
• Couples with a fertility concern. A better semen analysis in healthy volunteers is not a treatment for infertility. Male infertility has many causes — among them varicocele, hormonal disorders, infections and genetic conditions — that dietary change does not address, and questions about investigation and treatment belong with a clinician.

Practical information on buying, storing and preparing walnuts is on the main walnuts page, and the soaking question on the soaking and phytates page.

Connections

• Nuts — all the nut pages
• Walnuts — the main topic page
• Walnuts — Benefits Deep Dive — the hub for these articles
• Walnuts: ALA Omega-3 and Brain Health — the omega-3 that changed in the trial
• Walnuts for Heart Health: The PREDIMED Trial
• Walnuts and Cognitive Aging: The WAHA Trial
• Walnuts: Gut Microbiome and Urolithins
• Walnuts: Nutrient Profile
• Almonds and Hazelnuts — the other two nuts in FERTINUTS
• Male Infertility — causes, tests and treatments
• Infertility — the couple-level picture
• Erectile Dysfunction
• Zinc — a mineral linked with semen quality
• Selenium — an antioxidant mineral studied for sperm
• Vitamin E — the membrane antioxidant in walnuts
• Omega-3 Fatty Acids
• Carnitine and Male Fertility
• Meiosis and Gametes — animation of how sperm are made

Key Research Papers

1. Robbins WA, Xun L, FitzGerald LZ, Esguerra S, Henning SM, Carpenter CL. Walnuts improve semen quality in men consuming a Western-style diet: randomized control dietary intervention trial. Biol Reprod. 2012;87(4):101. PubMed PMID: 22895856
2. Salas-Huetos A, Moraleda R, Giardina S, Anton E, Blanco J, Salas-Salvadó J, Bulló M. Effect of nut consumption on semen quality and functionality in healthy men consuming a Western-style diet: a randomized controlled trial. Am J Clin Nutr. 2018;108(5):953-962. PubMed PMID: 30475967
3. Salas-Huetos A, James ER, Salas-Salvadó J, Bulló M, Aston KI, Carrell DT, Jenkins TG. Sperm DNA methylation changes after short-term nut supplementation in healthy men consuming a Western-style diet. Andrology. 2021;9(1):260-268. PubMed PMID: 32966683
4. Salas-Huetos A, Muralidharan J, Galiè S, Salas-Salvadó J, Bulló M. Effect of Nut Consumption on Erectile and Sexual Function in Healthy Males: A Secondary Outcome Analysis of the FERTINUTS Randomized Controlled Trial. Nutrients. 2019;11(6):1372. PubMed PMID: 31248067
5. Dávila-Córdova E, Babio N, Valle-Hita C, et al. Nut Consumption and Sperm Quality in Healthy Men: Results From the Led-Fertyl Study. Andrology. 2026;14(7):2262-2273. PubMed PMID: 41744493
6. Cardoso BR, Fratezzi I, Kellow NJ. Nut Consumption and Fertility: a Systematic Review and Meta-Analysis. Adv Nutr. 2024;15(1):100153. PubMed PMID: 37977328
7. Salas-Huetos A, Bulló M, Salas-Salvadó J. Dietary patterns, foods and nutrients in male fertility parameters and fecundability: a systematic review of observational studies. Hum Reprod Update. 2017;23(4):371-389. PubMed PMID: 28333357
8. Aitken RJ. Free radicals, lipid peroxidation and sperm function. Reprod Fertil Dev. 1995;7(4):659-668. PubMed PMID: 8711202
9. Hosseini B, Nourmohamadi M, Hajipour S, et al. The Effect of Omega-3 Fatty Acids, EPA, and/or DHA on Male Infertility: A Systematic Review and Meta-analysis. J Diet Suppl. 2019;16(2):245-256. PubMed PMID: 29451828
10. Coffua LS, Martin-DeLeon PA. Effectiveness of a walnut-enriched diet on murine sperm: involvement of reduced peroxidative damage. Heliyon. 2017;3(2):e00250. PubMed PMID: 28239673
11. Ikwuka DC, Anyaehie BU, Nwobodo E, et al. Ameliorative effects of African walnut on nicotine-induced reproductive toxicity in rat model. International journal of health sciences. 2021;15(1):3-8. PubMed PMID: 33456436
12. Sadogh A, Gorji N, Moeini R. Herbal foodstuffs in Avicenna's recommended diet to improve sperm quality and increase male fertility; an evidence-based approach. Journal of complementary & integrative medicine. 2021;19(1):47-70. PubMed PMID: 33544522

PubMed Topic Searches

1. PubMed: walnuts and sperm
2. PubMed: nut consumption and semen quality
3. PubMed: walnut oil and testicular toxicity in rats
4. PubMed: sperm lipid peroxidation and polyunsaturated fats
5. PubMed: omega-3 and male infertility trials

Featured Videos