In a recent systematic review published in the journal Frontiers in Nutrition, researchers from Spain investigated the effect of the Mediterranean diet on the quality of semen in men of reproductive age. They found that adherence to the Mediterranean diet could improve male reproductive health by positively influencing semen quality.
Study: Influence of the Mediterranean diet on seminal quality—a systematic review. Image Credit: leonori / Shutterstock
Background
Fertility research has surged as about 15% of the global population, comprising 70 million reproductive-age couples, suffer from infertility across geographies and income groups. The World Health Organization investigated infertility across 25 nations and found that male factors contributed to about half of the couples, challenging the older notion that infertility is solely a female concern. The major causes of male infertility are impaired spermatogenesis, idiopathic causes, endocrine disorders, and altered sperm motility. Clinically investigating the cause of male infertility warrants thorough history, physical examination, and semen analysis. Additionally, non-modifiable factors such as genetics and age, alongside modifiable factors such as diet and lifestyle, are also known to influence male fertility.
Popular for its potential health benefits, the Mediterranean diet demonstrates positive associations with male reproductive health, including improved semen quality attributed to its anti-inflammatory and antioxidant properties. Evidence suggests that optimal adherence to this diet may lower the risk of various chronic diseases and potentially enhance male fertility by addressing metabolic factors affecting sperm function. Therefore, researchers in the present study conducted a systematic review to understand the effect of the Mediterranean diet on the quality of semen in men of reproductive age.
About the study
Data for this review were gathered through electronic searches in PubMed, the Cochrane Library, Scopus, and Web of Science, as well as reference lists. Full-text articles were screened based on criteria evaluated independently by two authors. The quality of studies was assessed using appropriate tools such as the Crombie criteria, the Newcastle-Ottawa Scale, and the PEDro scale. Interrater reliability was evaluated using Cohen’s kappa statistic.
Inclusion criteria were open-access articles published in English or Spanish between 2012 and 2022, focusing on men aged 18 to 55. The exclusion criteria excluded unrelated articles, systematic reviews, meta-analyses, conference proceedings, and studies of specific medical conditions. A total of 10 studies met the inclusion criteria, including a total of 2,032 participants across various countries, primarily Spain. Study designs included cross-sectional, cohort, case-control, and randomized controlled trials. Data extraction focused on variables such as nutrition status, diet, and semen quality assessment techniques. After extraction, data were grouped based on assessment techniques and associations between semen quality and the Mediterranean diet.
The quality of included studies was evaluated using the Cochrane Collaboration Risk of Bias tool, evaluating domains such as randomization, intervention deviations, missing outcome data, outcome measurement, selection of reported results, and other biases, classifying each item as having a low, high, or unclear risk of bias.
Nutrition status was evaluated using weight, height, body mass index (BMI), and waist circumference, while adherence to the Mediterranean diet was assessed using validated food frequency questionnaires or specific scores. Semen quality was primarily assessed through sperm concentration, motility, morphology, volume, total antioxidant capacity, and hormone levels. Some studies also explored chromosome stability, DNA (short for deoxyribonucleic acid) fragmentation, global sperm DNA methylation, microRNA (short for micro ribonucleic acid) expression, and reactive oxygen species.
Results and discussion
Six out of 10 studies demonstrated a positive association between semen quality and following the Mediterranean diet, particularly in parameters like sperm concentration, motility, and total sperm count. In three of them, men with higher adherence levels showed significantly higher semen quality. However, two studies found no significant association between Mediterranean diet adherence and semen quality.
The present study is the first to comprehensively investigate the positive link between the Mediterranean diet and semen quality. However, the study is limited by its small sample size, observational design, and low generalizability, with evidence quality rated as very low to moderate using the GRADE (short for Grading of Recommendations, Assessment, Development, and Evaluation) system. Risk of bias assessment for randomized controlled trials indicated one trial with low risk and another with bias concerns related to intervention deviations and result evaluation. Further research with larger sample sizes and randomized controlled trials is warranted to confirm these findings.
Conclusion
In conclusion, healthy dietary habits, particularly adherence to the Mediterranean diet, are found to be associated with improved semen quality in men of reproductive age. This diet, rich in polyunsaturated fatty acids, antioxidants, and anti-inflammatory substances, may reduce oxidative stress and protect against its adverse effects on sperm. These findings highlight the importance of dietary counseling for couples planning a pregnancy or undergoing assisted reproductive technology. However, further research is necessary to explore the relationship between diet and semen quality, informing strategies for improved fertility and health outcomes.
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