A healthy amount of exercise in men can be beneficial. Physically active men who exercised at least three times a week for one hour typically scored higher in almost all sperm parameters in compare to men who have sedentary lifestyle. Moderately physically active men had significantly better sperm morphology (shape). Other parameters including total sperm number, concentration, and velocity also showed a similar trend but were not nearly as marked.
Obese men have lower circulating testosterone which affects sperm production known as spermatogenesis. This affects the quantity and quality of a mans sperm.
Obese men have increased risk of oligozoospemia, having fewer than 15 million sperm per millilitre of semen, and far fewer motile sperm than a man of healthy weight. Sperm with high amounts of damaged DNA are significantly more common in obese men than in normal weight men. Ejaculate volume is also affected. With lower count of sperm and their quality, there is lower possibility to concieve naturally.
Altered male hormones will can also give erectile dysfunction which is the major cause of infertility in obese men.
Sedentary lifestyle is associated with obesity. Gametes (a cell that fuses with another cell during conception in organisms that sexually reproduce), embryos and uterus seem to be negatively affected by the abnormal hormonal and metabolic environment present in obese women. Obesity has been associated with impaired fertility, furthermore obese women has experience of disturbance in the menstrual cycle, hypothalamic-pituitary ovarian axis (a complex set of direct influences and feedback interactions among three endocrine glands: the hypothalamus, the pituitary gland and the ovaries) and unfortunately a very high prevalence of infertility.
Prolactin has been proposed to play an important role in the pathophysiology of obesity. Prolactin (PRL) is one of several hormones that are produced by the pituitary gland. Prolactin levels increase during pregnancy causing the mammary glands to enlarge in preparation for breastfeeding and ready to secrete colostrums closely after delivery. During the first several months of breastfeeding, the higher basal prolactin levels also serve to suppress ovarian cyclicity. This is the reason why women who are breastfeeding do not get their periods and therefore do not often become pregnant.
Even mildly obese women have been found to display an enhanced prolactin secretion across the 24-h cycle as compared with normal-weight women. When examining the possible effect of obesity on elevated prolactin, which should be, spontaneous prolactin release has been shown to be significantly elevated in obese women in direct proportion to the size of the fat mass.
With high levels of prolactin in obese women, the ovulation may be also suppressed by the same mechanism, so there is no egg which can be fertilised.