Amenorrhea = no menstrual period
Oligomenorrhea = infrequent or scanty menstrual periods, specifically fewer than 6-8 periods a year.
When a woman burns more calories than she takes in by eating, her body will sense a "caloric deficit" and try to conserve its fuel for the more important vital organs, such as the heart, lungs, and kidneys. Your body simply not put energy to maintaining your reproductive system.
This condition is very common in athletes and in women who exercise or diet excessively. FHA is also very common in women who suffer from anxiety, since a constant state of anxiety expends a lot of energy. Another common personality trait is women who are perfectionists and/or who are higher achievers.
Excessive exercise (women athletes), eating disorders (anorexia nervosa, bulimia nervosa), disordered eating (excessive dieting) and emotional stress are the most common causes of Functional Hypothalamic Amenorrhea (FHA) or Functional Hypothalamic oligomenorrhea.
** NOTE: FHA and PCOS often co-exist. Please see the PCOS webpage