By Cristina Mestre Ferrer BSc, MSc (embryologist).
Last Update: 12/23/2014

During the last years, the number of people suffering from overweight has increased. Due to this, the negative consequences that a high body mass index has on the organism, have been observed.

It’s estimated that between 25% and 30% of fertility problems are related to alterations in the seminal quality. In some cases, obesity can be at fault for the absence of healthy spermatozoa to fertilise the egg, and therefore, that there are problems for achieving pregnancy.

It’s been proved that a BMI over 30 in women decreases the likelihood of pregnancy, and everything points out to the fact that obesity may affect seminal quality, hence decreasing the likelihood of getting pregnant.

Hormonal levels with overweight

Obesity in men

In men, obesity doesn’t affect in the same way as it does in women. In the cases of female obesity, overweight has a bigger impact on fertility and, with a weight loss, an immediate improvement is observed. In many cases, ovulation is naturally re-established, solving many diagnoses of polycystic ovary syndrome.

In men, the impact that obesity has on the spermatozoa is less, if observed individually, but if observed at the population level, it can be a cause of male infertility, since it alters the normal levels of production and maturation of the sperm.

In the studies that have been carried out up to now, it hasn’t been observed a single cause that explains the lower quality of the sperm in obese men, but the most altered parameters are:

  • Less seminal volume.
  • Less concentration of spermatozoa.
  • Worse maturation of the spermatozoa.
  • Higher index of spermatic DNA fragmentation.

The most likely explanation is that the organism is not able to generate enough hormones quantity to normally carry out spermatogenesis. Men with a BMI higher than 30 tend to have low levels of male sex hormones, especially testosterone, which would affect the production of spermatozoa.

Percentage sperm alterations

Sperm alterations

Apart from a decrease in the sperm concentration, the quality of the spermatozoa formed is lower, since the created spermatozoa have a high index of DNA fragmentation, which makes them unstable and unable to reach the egg and fertilise it. Furthermore, the average life of these spermatozoa is shorter.

If severe seminal alterations exist, such as azoospermia – absence of spermatozoa when ejaculating –, the hormonal levels should be checked, just in case it is due to hypogonadotropic hypogonadism, i.e. no sexual hormones are being produced or their levels are too low.

It’s been proved that, if men lose weight by exercising and keeping a balanced diet, the seminal parameters improve significantly. This means that, if after the sperm analysis, the improvement in the seminal quality is confirmed, they can try to achieve pregnancy naturally, without turning to assisted reproduction techniques. However, if this weight loss is due to a surgical intervention, such as stomach stapling or the insertion of an intra-gastric balloon, the parameters won’t improve, although the cause is not known.

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Authors and contributors

 Cristina Mestre Ferrer
BSc, MSc
Embryologist
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information
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