According to the study, overdoing it on cardio at the gym could harm fertility in men, as being too lean was actually shown to be worse for sperm count than being overweight. Men with a body mass index of 18.5kg/m2 or below were found to have sperm counts which were seven per cent lower than men of a normal weight. In comparison, men who were overweight had sperm counts that were four per cent lower than those of a normal weight. “Most previous studies have focused on the influence of obesity or being overweight on semen quality, and evidence on the association between underweight and semen quality is rare,” said lead author Dr Yuewei Liu, of the Huazhong University of Science and Technology.
Our study provides evidence that being underweight and overweight are both associated with lower semen quality, and highlights the importance of maintaining a normal weight for men
Dr Yuewei Liu
“Our study provides evidence that being underweight and overweight are both associated with lower semen quality, and highlights the importance of maintaining a normal weight for men.”
The research, published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology, looked at 3,966 male donors at a sperm bank in China, who were weighed when they donated.
The men were split into four groups: ‘Underweight’ – with a BMI of 18.5kg/m2 or below; ‘Normal weight’ – with a BMI of 18.5–24.9kg/m2; ‘Overweight’ – with a BMI of 25–29.9kg/m2; and ‘Obese’ – with a BMI of 30kg/m2 and above.
In skinny men, ‘sperm concentration’ was down three per cent, ‘total sperm’ was down 6.7 per cent, and ‘total motile sperm’ was down 7.4 per cent compared to the ‘normal weight’ group.
Larger men faired slightly better in two categories, with ‘total sperm’ down by just 3.9 per cent and ‘total motile sperm’ down 3.6 per cent.
Sperm concentration, however, was down 4.2 per cent – more than those in the ‘underweight’ category.
“Around 70 per cent of men in the UK are classed as overweight, which is why the dangers of a very low BMI can often be under-represented,” said European fertility specialist Dr Hana Visnova.
“But just because fewer men are classed as underweight, it doesn’t make it any less of an issue when it comes to fertility.”
Your weight could also determine whether you’re granted access to NHS-funded IVF treatment, warns Dr Visnova.
Many Clinical Commissioning Groups (CCGs) look at male BMI and age when restricting access to IVF – with more than a quarter in England using a man’s BMI to determine referrals.
10 ways to boost your fertility
10 ways to boost your fertility.
10 ways to boost your fertility
Dr Visnova says that for many experts, the jury is still out on whether being obese affects sperm quality.
“There’s actually very little evidence to link obesity with sperm quality in men – and this warrants further study.
“There are, though, other things to consider when it comes to libido and sex drive. A high level of obesity indirectly influences sexual appetite.
“Obese patients may have high blood pressure and other health issues that may cause erectile dysfunction and libido impairment.”
Guidelines from the National Institute for Health and Care Excellence (NICE) list other factors to be taken into consideration when trying to improve male fertility.
They include cutting down on alcohol, caffeine and smoking, and avoiding wearing tight underwear, as “there is an association between elevated scrotal temperature and reduced semen quality”.
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