Weight, exercise, and why your period might be late

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Most women will have experienced the panic that comes with a delayed or missing period. Am I pregnant? Is there something wrong with me? Do I have an infection? And yet, missed or delayed periods are common and can occur for numerous reasons. Of course, very occasionally, you may find you miss a period or your period stops because of a medical problem. These can include polycystic ovarian syndrome, or thyroid problems.

Less widely discussed is the effect that exercise and weight can have on periods. Weight loss, and weight gain, can both cause periods to stop, as can intense exercise over a long period of time. But why is this, and is it dangerous?

Weight loss

Your menstrual cycle occurs thanks to a complicated pattern of hormonal changes and chain reactions that occur each month. Sudden and sustained loss of weight can disrupt these chain reactions and cause periods to stop, which is known as secondary amenorrhea, that is the absence of periods for at least three months following previously normal menstruation. However, losing a small amount of weight is unlikely to affect your menstrual cycle, as gynaecologist Dr. Felice Gersh points out. “The reality is that periods do not typically stop when weight is lost,” she says. “In fact, in overweight women, particularly those with polycystic ovary syndrome, periods often resume and become regular with weight loss.”

However, if someone loses a lot of weight over a prolonged period of time, they will likely lose a lot of body fat. The body can sense the amount of stored fat and therefore gauge the likelihood of success or failure of a pregnancy. “Everything in life is in some way directed towards the prime directive: reproduction and survival,” says Dr. Gersh. “If a woman is ill or starving, then she would make a poor candidate for pregnancy, so the body shuts that part down, hence no ovulation, no pregnancies, no menses.”

The exact process behind this involves a hitch in the process of the set of hormonal interactions that leads to a period. Sudden changes in weight can cause the hormone leptin, produced by fatty tissue, to drop, which can disrupt the menstrual cycle.1 Reduced fat stores also reduce thyroid levels but cause an increase of cortisol, which has a knock on effect on the reproductive hormones. Finally, weight loss can cause an increase in the hormone ghrelin, which, like leptin, causes a chain reaction resulting in diminished release of luteinising hormone and follicle-stimulating hormone, which are crucial for the menstrual cycle.2

This is why women with anorexia nervosa often have secondary amenorrhea, as they have incredibly low levels of body fat and essentially their body shuts down the systems that it doesn’t think it is healthy enough to support.3 However, someone women could potentially have a body weight in the “normal” range, and still stop menstruating, due to having low amounts of body fat (that is, low levels of easily accessible energy stores), despite not being underweight.

This is more likely if someone has a lot of muscle, but very little body fat, such as an athlete. Just because they are in the normal weight range doesn’t mean they are definitely going to ovulate. “Once again, this is all about the body trying to work out the probability that a pregnancy will be successful,” says Dr. Gersh. “This is why female ballet dancers, marathon runners, and gymnasts often have no periods.”

How does exercise impact menstruation?

There are two reasons why an athlete, or someone who has an extremely intense exercise regime, may not have a regular cycle, or may not have periods at all. Firstly, as mentioned above, athletes tend to have very low body fat. Secondly, considerable exercise can put the body under considerable stress, which itself can affect the menstrual cycle. “The body views that as a serious negative for a successful pregnancy,” says Dr. Gersh, “So the body shuts those systems down.”

The way that physical stress can stop periods from occurring works in a similar way that mental stress can cause amenorrhea. “The systems are all interconnected,” says Dr. Gersh. “The hypothalamic-pituitary-adrenal-ovarian axis is an amazingly complex system in which any one of the components can interrupt the whole. Stress works to increase cortisol and cortisol, over time, alters the gut. With leaky gut, the immune system is exposed to lots of endotoxin. This leads to an inflammatory state in the body, which leads to more cortisol. In turn, the high cortisol interferes with proper ovarian function.”

But how do prevent amenorrhea if you are an athlete, or if you do do a lot of exercise to the extent that it interferes with your menstrual cycle? Or do some professional athletes simply not menstruate? “There is a sweet spot for exercise,” says Dr. Gersh. “Too little or too much can cause harm. Extreme athletes suffer from severe oxidative stress to their bodies and will suffer significant consequences. Amenorrhea in an athlete is a powerful message that the amount of exercise they’re doing is too much and that instead of benefitting the body, it is causing them harm. Then, a decision must be made and priorities set.”

Weight gain

If being underweight stops periods, then it might sound odd that being overweight and obese can also cause secondary amenorrhea. However, when you have an excess of fat cells producing oestrone, a type of oestrogen, then this mimics pregnancy. So, as your body thinks you are pregnant, you will stop ovulating, but this excess of oestrone continues to build up the womb lining. This can break down from time to time, causing a heavy and longer period when it does eventually arrive. It is said that losing even just five percent of your body weight can mean your regular cycle returns.

“Obese people are typically highly inflamed, because adipose tissue is hormonally active,” adds Dr. Gersh. “When too much accumulates, particularly visceral or belly fat, it is highly inflammatory, and becomes infiltrated with inflammatory cells from the immune system.” These cells secrete inflammatory products called cytokines, which are like tiny messengers that act as though there is an infection to fight, when there isn’t one. Instead, however, an inflammatory state in the body occurs which raises the levels of insulin and IGF-1. These hormones can increase the ovarian production of testosterone, which can interfere with ovulation. The inflammatory cytokines can also be directly toxic to the ovaries themselves.

Can amenorrhea be dangerous?

Having amenorrhea over a period of time can cause significant health issues, and is not good for you. While certain “health” bloggers have claimed that exercising and restricting food intake to the point of amenorrhea is a good way of getting rid of “toxic periods”, this is wrong, and extremely dangerous advice, given that amenorrhea can cause a whole host of health issues later down the line.

“There are generally two types of secondary amenorrhea: ovarian production of oestrogen but no ovulation occurring, and no oestrogen production at all, which is due either to an early menopause or to hypothalamic-pituitary amenorrhea (shutdown),” says Dr. Gersh.

In the first instance, there is adequate oestrogen to provide basic maintenance of the parts of the body which need oestrogen, including the bones and muscles. However, the fact that there is no ovulation and no progesterone produced increases the risk of uterine cancer, breast cancer, and perhaps others.

“When amenorrhea occurs with no oestrogen being made, this opens the door for the early onset of cardiovascular disease, osteoporosis, depression, dementia, urinary tract infections and vaginal dryness,” says Dr. Gersh. “Both situations are very serious, and require a thorough evaluation.”

Ultimately, the menstrual cycle is a vital sign for women of reproductive age, and when a woman loses it, it is a message that the body is not optimally healthy. If your periods stop, or become irregular, and it does not appear to be due to your contraception, pregnancy, or breastfeeding, then it is important to seek the advice of your doctor to find out what could be causing it.


1. Fontana, R., and Della Torre, S., The deep correlation between energy metabolism and reproduction: a view on the effects of nutrition for women fertility, Nutrients, February 2016, vol 8, issue 2, pp 87

2. Budak, E., et al., Interactions of the hormones leptin, ghrelin, adiponectin, resistin, and PYY3-36 with the reproductive system, Fertility and Sterility, June 2006, vol 85, issue 6, pp 1563-1581

3. Fontana, R., and Della Torre, S., The deep correlation between energy metabolism and reproduction: a view on the effects of nutrition for women fertility, Nutrients, February 2016, vol 8, issue 2, pp 87

Imogen Robinson

Imogen was The Femedic’s original Deputy Editor. She joined The Femedic after working as a news reporter. Becoming frustrated with the neverending clickbait, she jumped at the chance to work for a site whose ethos revolves around honesty and empathy. From reading articles by doctors to researching her own, and discussing health with a huge variety of women, she is fascinated by just how little we are told about our own bodies and women-specific health issues, and is excited to be working on a site which will dispel myths and taboos, and hopefully help a lot of women.

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