No period—Is it because of my weight?


What should my normal body weight be? I am 4 feet 11 inches tall and I weigh 75 pounds presently. I think that I am underweight because I haven't had my period in almost a year. If I were of normal weight, what percentage of my calories should come from fat?

— Weight conscious

Dear Weight Conscious,

Kudos for asking questions about your health when you're concerned something may be off! To your first question, it's hard to say what a typical weight would be for someone based on height alone; a person's medical history along with a number of other variables factor into what weight (or weight range, rather) may be healthy for them. While your weight may be contributing to your lack of periods (i.e., amenorrhea), there is a range of other factors that may be at play (more on those in a bit!). For a more clear-cut answer to your question, it’s best that you speak with a health care provider about your weight, periods, and dietary needs that meet your lifestyle.

A commonly used tool to determine if someone is underweight, normal weight, or overweight using height and weight measures is the body mass index (BMI). If you're using BMI, it may indicate that you're underweight. However, keep in mind that the BMI calculation has been criticized by researchers and medical professionals as it doesn’t consider body composition (the distribution of muscle versus fat), and therefore isn't indicative of overall physical health. That means that even a professional athlete could be considered overweight, even though they tend to be in excellent physical shape. While BMI is not a be-all-end-all metric, it can be helpful to give you a general idea if you're underweight. Other factors that contribute to a lower body weight include genetics, high levels of physical activity, malnutrition, certain medicines, or medical procedures.

Low body weight may be the cause of amenorrhea (the absence of periods for at least three consecutive months) for some people. There’s evidence to suggest that substantially low body weight (specifically, ten percent or more under typical weight) can affect the body’s hormonal functions, and potentially stop ovulation. However, there is a multitude of other factors that may contribute to amenorrhea, including:

  • Medications: Side effects of certain contraceptive methods, antipsychotic medications, chemotherapy for various cancers, and allergy medications may lead to amenorrhea.
  • Lifestyle factors: Excessive physical activity or stress, specifically, rigorous activities which burn a lot of energy can interrupt a person’s menstrual cycle. Likewise, immense stress may temporarily inhibit the functioning of the hypothalamus—the part of the brain responsible for metabolic processes; subsequently, a person’s ability to ovulate and menstruate may be affected.
  • Hormonal imbalances: The menstrual cycle is regulated by hormones, including progesterone, estrogen, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Thus, when these hormones inappropriately fluctuate, there’s potential for it to disrupt the menstrual flow. These imbalances can arise from various health conditions, including polycystic ovary syndrome (PCOS), a benign pituitary tumor, an overactive or underactive thyroid, and premature menopause.
  • Eating disorders: When a person with anorexia or bulimia restricts or purges the food they eat, their body may become malnourished; this often results in significantly low levels of hormones necessary for menstruation, and may stop menstruation altogether. To that end, people with a family history of amenorrhea and eating disorders face a higher risk of later experiencing amenorrhea.
  • Lifecycle factors: Pregnancy, breastfeeding, and menopause will temporarily or permanently eliminate periods.

You may find it helpful to take note of any symptoms you're experiencing in order to discuss your concerns with a health care provider. Some questions that may help you with this may include: What medications (if any) do you take on a regular basis? What are your eating habits like? What type of physical activity routine do you have? Have you recently switched your exercise routines? Have you recently had a child? What were your periods like before they stopped? Thinking through some of these questions, as well as any other symptoms you may be experiencing, may help your provider figure out the cause of your amenorrhea and offer the best course of action.

To answer your question about calories from fat, research suggests that roughly 20 to 30 percent of a person’s calories come from unsaturated fats. However, rather than focusing on the percentage of calories from unsaturated fat, it might be easier and more beneficial to focus on the general number of calories and the type of fat you consume. 

With all of this said, speaking with a health care provider about your weight and experience with amenorrhea may provide the most clarity. They may choose to run some tests to explore and address the potential cause(s). Similarly, talking with a registered dietitian may provide some reassurance and guidance on establishing a healthy pattern of eating. Hopefully, with the help of your providers and these tips, you’ll feel more equipped to address your concerns.

Take care!

Last updated Dec 16, 2022
Originally published Mar 19, 1994

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