Proof–of–principle experiments in mice and lower primates demonstrate a clear association between leptin, energy balance and reproductive health. Obese individuals often demonstrate aberration in leptin signaling. Either they have higher sustained levels of leptin (it is produced in peripheral fat cells) and or demonstrate leptin resistance (similar to having a key that does not quite fit the lock, and thus is ineffective).
Sustained, elevated levels of leptin (hyperleptinemia) interfere with menstrual cyclicity through inhibiting follicular growth and egg development and maturation. In turn, ovulation is not signaled and does not occur. It has been hypothesized that leptin may be associated with PCOS (polycystic ovarian syndrome) and maybe involved in the metabolic issues associated with the syndrome itself. These hypothesis need further testing for validation.
However, it is not just the woman who’s reproductive function may be affected. In fact, men are not immune to the effects of hyperleptinemia. Total percentage of fat (fat mass) and leptin levels are inversely proportionate to blood testosterone levels.
To translate this complicated symphony of hormones and reproduction into daily function can be mind-bending. Elevated BMIs are detrimental to reproductive function. IVF outcomes are clearly decreased as BMI increases. However, too low of a BMI demonstrates the same phenomenon. It is for this reason, that we consider BMI as an essential component to the equation with our common goal of a healthy pregnancy and outcome.