Men with more kilos than necessary are at greater risk of infertility, shows a study that also says they could suffer low sperm count and poor quality seed, the precursor to infertility.
The study, published in the journal Human Reproduction last week, found that greater body mass index (BMI) was closely associated with measures of lower sperm count and overall poor semen quality.
BMI is the value derived from the mass and height of an individual and is often calculated by dividing the mass with the square of the height of the person.
The collateral damage of overweight and obesity (a BMI above 25 and 30, respectively) should concern men who fall within that range and wish to continue having children, the researchers argue.
The scientists found that men generally do not mind living with a wider waistline until they learn that they cannot have children. They also said the reduction of the sperm could be a result of excessive temperatures in the scrotum, which rises in fat people.
Dr Zhide Ding of Embryology, Genetics and Developmental Biology, Shanghai Key Laboratory for Reproductive Medicine, School of Medicine, Shanghai Jiao Tong University, in Shanghai, China, said obesity is a metabolic disorder resulting from behavioural, environmental and heritable causes.
Other risk factors of obesity include hypertension, diabetes, cardiovascular disease, sleep apnea, respiratory problems and cancer.
Meanwhile, the negative impact of obesity on male reproduction is gradually being recognised. Clinical investigations and animal experiments show obesity is correlated with reductions in sperm concentration and motility.
"It is also blamed for the increase in sperm DNA damage and changes in reproductive hormones," said Dr Zhide.
The study revealed that several factors could explain the effects of obesity on sperm functions and male subfertility -- including the excessive conversion of androgens into oestrogens in redundant adipose tissue causing sexual hormone imbalance, subsequently resulting in hypogonadism.
Hypogonadism occurs when sex glands produce little or no sex hormones.
The sex glands, also called gonads, are primarily the testes in men and the ovaries in women.