Menstruation and weight: Why maintaining balance is crucial for women's health

Menstrual cycles are influenced by body weight and hormonal levels. Underweight or overweight conditions can disrupt ovulation and lead to irregular periods.

You may have noticed that changes in weight are sometimes accompanied by changes in your period. But what does one really have to do with the other? Maintaining a healthy weight is key to regular menstruation. Here’s why – and when to talk to your doctor.

The role of hormones

The menstrual cycle – including when you bleed and ovulate – is regulated by a balance of hormones, particularly oestrogen. The ovaries are connected to the brain through a hormonal signalling system. This acts as a kind of “chain of command” of hormones controlling the menstrual cycle.

The brain produces a key hormone, called the gonadotropin-releasing hormone, in the hypothalamus. It stimulates the release of other hormones which tell the ovaries to produce oestrogen and release a mature egg (ovulation).

But the release of the gonadotropin-releasing hormone depends on oestrogen levels and how much energy is available to the body. Both of these are closely related to body weight. Oestrogen is primarily produced in the ovaries, but fat cells also produce oestrogen. This is why weight – and more specifically body fat – can affect menstruation.

Can being underweight affect my period?

The body prioritises conserving energy. When reserves are low it stops anything non-essential, such as reproduction. This can happen when you are underweight, or suddenly lose weight. It can also happen to people who undertake intense exercise or have inadequate nutrition. The stress sends the hypothalamus into survival mode. As a result, the body lowers its production of the hormones important to ovulation, including oestrogen, and stops menstruation.

Being chronically underweight means not having enough energy available to support reproduction, which can lead to menstrual irregularities including amenorrhea (no periods at all). This results in very low oestrogen levels and can cause potentially serious health risks, including infertility and bone loss.

Missing periods is not always a cause for concern. But a chronic lack of energy availability can be, if not addressed. The two are linked, meaning understanding your period and being aware of any prolonged changes is important.

How about being overweight?

Higher body fat can elevate oestrogen levels. When you’re overweight your body stores extra energy in fat cells, which produce oestrogen and other hormones and can cause inflammation in the body. So, if you have a lot of fat cells, your body produces an excess of these hormones. This can affect normal functioning of the uterus lining (endometrium).

Excess oestrogen and inflammation can interfere in the feedback system to the brain and stop ovulation. As a result, you may have irregular or missed periods. It can also lead to pain (dysmenorrhea) and heavier bleeding (menorrhagia).

Being overweight can sometimes worsen premenstrual syndrome as well. One study found for every 1 kg increase in height (m²) in body mass index (BMI), the risk of premenstrual syndrome went up by 3%. Women with a BMI over 27.5 kg/m² had a much higher risk than those with a BMI under 20 kg/m².

What else might be going on?

Sometimes weight changes are linked to hormonal balances that indicate an underlying condition. For example, people with polycystic ovary syndrome may gain weight or find it hard to lose weight because they have a hormonal imbalance, including higher levels of testosterone.

The syndrome is also associated with irregular periods and heavy bleeding. So, if you notice these symptoms, it’s a good idea to talk to your doctor. Similarly, weight changes and irregular periods in midlife might signal the start of perimenopause, the period before menopause (when your periods stop altogether).

When should I worry?

Small changes in when your period comes or how long it lasts are usually harmless. Similarly, slight fluctuations in weight won’t usually have a significant impact on your period – or the changes may be so subtle you don’t notice them.

But regular menstruation is an important marker of female health. Sometimes changes in flow, regularity or the pain you experience can indicate there’s something else going on. If you notice changes and they don’t feel right to you, speak to a health care provider.