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Obesity (BMI ≥ 30) is a potential cause of male infertility and a poor prognostic factor during a fertility journey. An increase in male BMI is associated with lower birth rates during artificial insemination or in vitro fertilisation (IVF) procedures. Excessive weight must therefore be actively cared for before any attempt at fertility treatment.
Obesity - a body mass index (BMI) greater than or equal to 30 kg/m2 - is a genuine public health problem whose prevalence continues to rise, with major consequences for health and quality of life. In a fertility journey, 50% of failures are linked to male factors, notably because of the increase in male obesity. Excess weight impairs sperm quality and reduces male fertility.
There are many obesity-related factors that aggravate male infertility:
Obesity, especially abdominal one, leads to alterations in the hypothalamic-pituitary axis secondary to various endocrine mechanisms. In obese men, there is a significant reduction in testosterone levels and a significant increase in oestrogen levels, contributing to impaired spermatogenesis. Other studies have also shown that obesity may alter spermatogenesis through a direct action on the testicle, with malfunctioning of Leydig and Sertoli cells (cells located in the testicle) contributing to a drop in male fertility.
2- Testicular warming
Finally, excessive testicular heating may be linked to increased scrotal adipose tissue and abdominal obesity in the sitting position. This increase in testicular temperature is likely to alter spermatogenesis, resulting in a lower sperm count and therefore a reduction in male fertility.
Obesity and spontaneous fertility
With regard to spontaneous fertility, a 2006 study analysed data collected between 1993 and 1997 on more than 50,000 men in Iowa and North Carolina. The authors showed that a three-point increase in BMI was correlated with a moderate but significant increase in the risk of infertility .
Another study published in 2013 , involving more than 13,000 men, also reported on the impact of BMI on sperm count. It appears that overweight and obesity are associated with an increased risk of a lower sperm count (figure 1). This risk is significantly increased in obese men (BMI > 30) and doubled in morbidly obese men (BMI > 40) compared with men with a normal BMI.
Risk of spermogram alteration according to BMI, according to Sermondade et al.
Obesity and fertility
In the context of a fertility journey, male obesity could significantly influence the outcome of attempts. A review of the literature published in 2018 including more than 14,000 cycles of fertility showed that an increase in weight in men is associated with a significant decrease in the rates of clinical pregnancies and live births during IVF or artificial insemination treatment.
Obesity is therefore a potential cause of male infertility and a factor with a poor prognosis in assisted reproduction. It must therefore be actively cared for in order to optimise the chances of pregnancy.
 Sallmen M, Sandler DP, Hoppin JA, Blair A, Baird DD. Reduced fertility among overweight and obese men. Epidemiology 2006; 17(5):520–3.
 Sermondade N, Faure C, Fezeu L, et al. BMI in relation to sperm count: an updated systematic review and collaborative meta-analysis. Hum Reprod Update 2013;19(3):221–31.
 Mushtaq R, Pundir, Achilli C, Naji O, Khalaf Y, El-Toukhy T. Effect of male body mass index on assisted reproduction treatment outcome: an updated systematic review and meta-analysis. Reprod Biomed Online. 2018 Apr; 36(4):459-471
Dr. Laura Alter, pharmacist-biologist,
Former intern at the Hôpitaux de Paris, former assistant at the Hôpitaux de Paris,
University Hospital Assistant in the fertility center at Poissy Hospital,
Specialising in reproductive biology and fertility preservation.