I am an elite female athletes and I have a pill specially formulate for me by an endocrinologist which is just estrogen to maintain my bone health as I don't get periods ordinarily. My endocrinologist has said this is due to miles and low body fat.
The poster who said that body fat isn't what determines the absence of period, it is the amount of food you consume, that is wrong. Low body fat % in female sends a message to the pituitary gland to signal that the body is in starvation and is not capable of childbirth. Therefore, the pituitary gland shuts down to stop the production of female hormones.