. How Does Reduced Energy Availability Affect Hormonal Control of Female Reproduction? How Are Hormonal Changes Related to Energy Intake?

Much research has been done on the effects of reduced energy availability on hormonal control of female reproduction. One study analyzed groups of male and female rats divided into three different diet groups for over six months. The first group had a normal diet and acted as the control, the second group had a 20 to 40 percent caloric restriction (CR), and the third group underwent intermittent fasting (IF). The females in the 40 percent CR group were emaciated, ceased cycling, began showing endocrine masculinization, had a heightened stress response, increased spontaneous activity, improved learning and memory, and maintained elevated levels of circulating brain-derived neurotrophic factor (Martin et al). They concluded that lowering body weight caused elevation of corticosterone levels, thus suggesting a heightened activation of the hypothalamic-pituitary-adrenal axis. They also noted reduced gonad size and elevated testosterone levels in accordance to the ceased cycling. Rats in the 40 percent CR group also showed enhanced performance in cognitive testing. All of these alterations in physiology and behavior suggest that the female is preparing herself for survival in an environment that is scarce in food. Evolutionarily, women are more sensitive to these changes because they must obtain food not only for themselves, but for their offspring as well. Thus, the body goes into a survival mode that diverts energy from reproductive processes and focuses them toward increasing the chance of survival (Martin et al).
Another study done in 2006 aimed to understand the hormonal effect that limited energy availability had on female reproduction. They analyzed women with ceased ovulation who were underweight or performed strenuous exercise. These women showed lower levels of LH, leptin, and estradiol. They also had gonadotropin pulses at too low of frequencies to maintain antral follicular development until ovulation. To confirm this, the women were injected with LH to...