Low body fat stores lead to reduced leptin signaling, shutting off hormones that stimulate ovulation and sperm production, causing anorexic individuals to stop menstruating.

“when they're sufficient levels of body fat and leptin circulating in the blood. And that leptin signal gets to the brain, the hypothalamus and the pituitary gland register that signal. And in a completely subconscious way, trigger the deployment of eggs in females and the production of sperm in males.”

“So when body fat stores are very low, the reason why periods shut off or sperm production is reduced or even shut off is because there's not enough leptin getting to the hypothalamus and to the pituitary and they shut off the signals, the hormones, things like gonadotropen releasing hormone, luteinizing hormone, follicle stimulating hormone that travel to the ovar to the testes and cause the ovary and testes to ovulate or to produce more sperm.”