In recent years, the incidences of obesity, diabetes mellitus and male factor infertility have increased in the general population. Obesity, which can lead to metabolic syndrome, is characterized by elevated leptin levels; diabetes mellitus is characterized by decreased insulin levels or insulin insensitivity. A large body of evidence suggests that insulin and leptin play a role in the physiology of human reproduction. Insulin and leptin deficiencies have been shown to affect reproductive function negatively in humans and animal models. These hormones are thought to affect male reproduction at multiple levels due to their effects on endocrine control of spermatogenesis and spermatogenesis itself, as well as on mature ejaculated spermatozoa.