Lower Semen Quality Among Men in the Modern Era-Is There a Role for Diet and the Microbiome?

The prevalence of infertility is increasing worldwide; poor nutrition, increased sedentary lifestyles, obesity, stress, endocrine-disrupting chemicals, and advanced age of childbearing may contribute to the disruption of ovulation and influence oocyte and sperm quality and overall reproductive health. Historically, infertility has been primarily attributed to female factors, neglecting the importance of male fertility; this has resulted in an incomplete understanding of reproductive health. Male factors account for 40-50% of infertility cases. In half of these cases, the proximal cause for male infertility is unknown. Sperm contributes half of the nuclear DNA to the embryo, and its quality is known to impact fertilisation rates, embryo quality, pregnancy rates, risk of spontaneous miscarriage, de novo autosomal-dominant conditions, psychiatric and neurodevelopment conditions, and childhood diseases. Recent studies have suggested that both the microenvironment of the testes and diet quality may play an important role in fertility; however, there is limited research on the combination of these factors. This review summarises current known causes of male infertility and then focuses on the potential roles for diet and the seminal microbiome. Future research in this area will inform dietary interventions and health advice for men with poor semen quality, potentially alleviating the need for costly and invasive assisted reproduction treatments and allowing men to take an active role in the fertility conversation which has historically focussed on women individually.