Obesity represents a significant global public health challenge, which not only elevates the risk of mortality but also increases the likelihood of chronic diseases. The ongoing obesity epidemic has led to a growing recognition of the detrimental effects of excessive adipose tissue accumulation on male reproductive health. Substantial evidence indicates that obesity adversely affects sperm quality, thereby impairing male fertility. Specifically, obesity is associated with compromised spermatogenesis, erectile dysfunction, and detrimental effects on offspring fertility parameters. These effects are mediated through various mechanisms, including alterations in the hypothalamic–pituitary–gonadal axis, inflammation within the reproductive system, localized caloric excess in reproductive tissues, epigenetic modifications, disruptions in gut microbiota, and heightened oxidative stress levels. While the molecular alterations associated with obesity have been extensively documented, the precise mechanisms by which obesity influences male reproductive function remain inadequately understood. This article aimed to review the classification and distribution of adipose tissue in obesity, the impact of obesity on male fertility, and the potential mechanisms through which obesity affects male reproductive health, thereby offering insights into the prevention and treatment of obesity-related male fertility issues.

Objectives: This study aimed to investigate the mechanisms underlying impaired sperm motility in high-fat diet (HFD)-induced obesity. Methods: Six-week-old male C57BL/6J mice were used to establish an HFD-induced obesity model. Sperm motility and male reproductive function were then evaluated. Macrophage polarization was evaluated by flow cytometry, and key differentially expressed genes were identified by RNA-seq analysis of epididymal adipose tissue, the epididymis, and testes. Finally, pyruvate carboxylase (PC) and the PC inhibitor erianin (Eri) were used to examine the role of adipocyte-derived PC in regulating macrophage polarization. Results: HFD-induced obese mice exhibited abnormal testicular and epididymal morphology, with reduced sperm motility and viability. Flow cytometry revealed that macrophages were polarized toward the M1 phenotype in epididymal adipose tissue and the epididymis in the HFD group. RNA-seq analysis demonstrated that PC was the most significantly upregulated gene in epididymal adipose tissue. Furthermore, PC expression increased during adipocyte maturation in vitro. Mature adipocytes promoted macrophage polarization toward the M1 phenotype, while Eri attenuated this effect. In addition, supernatants from LPS-induced M1 macrophages contained elevated levels of inflammatory cytokines and significantly reduced sperm motility and viability. Conclusions: HFD-induced obesity impaired sperm quality and male reproductive function. The underlying mechanism may involve increased PC expression, which drives epididymal macrophages toward M1 polarization and triggers local chronic inflammation, ultimately compromising sperm motility and viability.