Why Your Period Makes You Poop!

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Ladies, have you ever felt bloated or backed up the week before your menstrual cycle? What about noticing diarrhea at the start of your menstrual cycle? I know I have. If you’ve been or are pregnant, have you noticed major changes in your digestive system and bathroom behaviors? Below I explore the connection between hormones and changes in your bowel movements.


Vocabulary! Gastrointestinal Motility is what we should be aware of when reflecting on this research. It is defined as the time it takes for material to move between one segment of your intestinal tract to the next. The way that material moves through your intestines is through the process of peristalsis otherwise known as muscle contraction of the smooth muscles which line your digestive system. As these muscles contract material is propelled from from one segment to the next. So, if ingested food takes longer to move between segments due to a change in the timing of peristalsis, you can see that the end result would be constipation. Conversely, if material moves quickly from one segment to the next due to increased peristalsis the end result may be moderate to severe diarrhea.



Understanding intestinal tract timing affects the outcome of bowel movements, which leads us to triggers, which then affect this timing. The main hormones that affect the GI system and timing are known as Progesterone and Prostaglandins and the amounts of these generated during both your monthly menstrual cycle as well as during pregnancy can result in dramatic changes in our bowel movements.


During your menstrual cycle progesterone is released during ovulation to help prepare the body for pregnancy. If an egg is fertilised then progesterone is a key hormone in stimulating the growth of blood vessels that supply the lining of the womb where the fertilised egg will settle. Progesterone further relaxes the smooth muscles of the uterus allowing for expansion and pregnancy. It is this increase in progesterone that impairs gastric motility and leads a person to feeling constipated and bloated.1



If the egg is not fertilized, then estrogen and progesterone levels drop sharply. The lining of the uterus sheds (starting your period) releasing prostaglandins. Prostaglandins play the opposite role of progesterone. Where progesterone relaxes the uterus, prostaglandins in turn cause the uterus to contract. The contraction of the uterus forcing everything to move towards an exit and this includes your intestines and bowels.


Depending on the hormone levels released we can now see how volatile our GI system can become the days leading up to and during our menstrual cycle. This volatility is one of the main reasons why we may experience diarrhea.


These hormones play a crucial role during pregnancy and so many of the same concepts detailed above apply.


Constipation is the second most common gastrointestinal complaint during pregnancy after nausea.2 During pregnancy Progesterone levels continue to rise for the first 36-38 weeks of pregnancy and then begin to plummet as the due date approaches. During the second and third trimester, the increase in progesterone causes smooth intestinal muscle relaxation to occur and we now know this can cause constipation. A study released in 2016 (conducted on female rats due to the inherent risks of human trials) found that GI motility in females slowed measurably when the subjects were exposed to high progesterone levels.3


Most telling of all during pregnancy is what having loose stools can mean. Loose stool is one of the key signs that labor is imminent and it important to be aware of your bowel movements throughout your pregnancy with specific mindfulness towards any changes in frequency or constipation. As we’ve discussed, your body releases prostaglandins to help soften your cervix, this in turn also causes changes to your GI system and softens your stool.


During early labor doctors may use prostaglandin suppositories to facilitate labor and contractions. Stay calm during this process but also stay close to the bathroom as this pre-labor sign indicates you should get ready to welcome your new baby to the world!


So, what can we do to help or change these symptoms? We can start by paying attention to our bowel movements and relating them to our menstrual cycles. Our patterns will become more predictable as we grow to understand our bodies and the role our hormones play every month.


I leave you with one especially important tip, be mindful of your insoluble fiber intake and proper bowel positioning; these can greatly help reduce bloating and cramping that may occur due to increased constipation. We can’t change the way our bodies function very much, but understanding what’s going on can provide clues to ways we can make out monthlies easier to manage. Talking to a physical therapist about ongoing issues can make a significant positive impact in your daily life. Girls just want to have fun!


For more information check out this blog for the right way to poop and this one for additional information on hormones here.





  1. Gill R, C, Murphy P, D, Hooper H, R, Bowes K, L, Kingma Y, J, Effect of the Menstrual Cycle on Gastric Emptying. Digestion. 1987;36:168-174
  2. Cullen GO’Donoghue DConstipation and pregnancy. Best practice & researchClinical Gastroenterology.2007;21(5):80718.
  3. Matos JF, Americo MF, Sinzato YK, et al. Role of sex hormones in gastrointestinal motility in pregnant and non-pregnant rats. World Journal of Gastroenterology. 2016;22(25):5761-5768

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