Many anorexic girls and women either never get their period or their period stops due to extreme weight loss. But for most women menstruation will start up when they begin to gain weight. When a woman's percentage of body fat falls below a certain minimum her body doesn't produce the levels of hormones necessary to stimulate ovulation. Rapid weight loss and undernourishment leads a woman's body into a state of emergency and she will not menstruate if she is just barely surviving. Low weight and weight loss is also associated with ovulatory dysfunction and thus infertility.
Obesity has a strong association with infertility and menstrual irregularities.
Group treatment programs that assist obese women with diet and exercise plans have shown return of fertility in many patients. Furthermore elevated risk are not confined to those acquiring their overweight or underweight in adulthood. Many are related to fatness or thinness in childhood or adolescent. Teenage obesity and thinness on fertility has been emphasized. In Lake, Powers and Cole s study they investigated the relationship between childhood and adolescent body mass index, in addition to that in adulthood with subsequent reproductive problems.