What Does Low Body Weight Have to Do With Irregular Periods?

And are there long-term health effects of irregular periods?

Irregular periods can take many different forms, but one of the more common ones is called “oligomenorrhea,” or abnormally rare menstrual periods. The term literally means “infrequent monthly flow.” The American Society for Reproductive Medicine recommends an evaluation for patients with oligomenorrhea, defined as less than nine cycles a year. Let’s review here oligomenorrhea that is related to low body mass.

What is low body weight?

According to the World Health Organization (WHO), body mass index (BMI) of less than 18.5 kg/m2 is considered abnormally low weight for adults. Body mass below 15 percent of ideal body weight (IBW) is one of the diagnostic criteria for eating disorders. While the concept of IBW originally came from actuarial life insurance tables and represents the presumably healthiest body mass for given height, BMI is the preferred way to assess body mass and is easily calculated as the ratio of the body mass in kilograms over the square of height in meters.

How common is low body weight?

Most common causes for low body weight-related amenorrhea include eating disorders, strenuous exercise and stress. It has been estimated that up to 1 percent of the population suffers from eating disorders. These disorders can take several forms, and appear to have varying relationships to irregular menstrual periods. Most sources include three eating disorders such as anorexia nervosa, bulimia nervosa and “eating disorder not otherwise specified,” yet anorexia is the only entity that is associated with abnormally low body weight and menstrual dysfunction.


Common features of eating disorders include negative attitudes about food, body image distortion and fear of fatness. Other common symptoms include distorted body image, menstrual dysfunction and fear of weight gain.

Why does it happen?

Recent studies suggest the key element involved in low weight related amenorrhea is stress. It appears that the adaptation to the chronic stress involved in food restriction plays a major role. The end result is functional hypothalamic amenorrhea (FHA), although less severe conditions appear to exist. In many clinical scenarios, it is difficult to differentiate the specific contributions of body weight, stress levels, and exercise to the amenorrhea or menstrual disturbances.


Overcoming conditions that lead to abnormally low body mass and related behaviors should involve an approach directed at behavioral modification. The long-term consequences of continuing to live in a state of chronic stress is likely related to the increased risk of heart disease in women with hypothalamic amenorrhea. Cognitive behavioral therapy is recommended in an attempt to mediate a permanent change and true healing. My colleague, Dr. Sarah Berga, is one of the pioneers who advocates stress-reduction for women with irregular menstrual periods that are thought to be due to low body weight.

Life-long consequences

The long term sequelae of amenorrhea caused by low body weight are only recently beginning to be recognized. Data from the Women’s Ischemia Syndrome Evaluation (WISE) study revealed that affected women have a much higher chance to develop coronary heart disease when they are older. This detrimental impact of menstrual irregularities on overall health is often under-appreciated by patients and doctors alike. More effort is needed to understand the mechanisms of this condition as well as to increase the public awareness of this malady and its remedies designed to reverse the pathological chain of events.