Diet restriction has negative impact on hypothalamus and decreases LH secretion causing amenorrhea (this has been observed in anorexia nervosa)
Diet restriction also causes low fat storage in body so less leptin released from the less fat as leptin is needed for pulsatile release of GnRH (Gonadotropin-Releasing Hormone), lean body leads to amenorrhea or oligomenorrhea.
added info
So, in obese people increased leptin causes precocious puberty