The following sections discuss the bodily changes that occur just before or during a menstrual period that may affect bowel movements.
Increased muscle contractions
Just before menstruation, the body releases hormones known as prostaglandins. These hormones stimulate muscle contractions in the uterus. These contractions help the body to shed the uterus lining.
At the same time, the period hormones may stimulate muscle contractions in the intestines and bowels, which are close to the uterus, causing more frequent bowel movements. They also reduce how well the body absorbs water, making the stool softer and increasing the risk of diarrhea.
It can be difficult to tell the difference between uterus cramps and stomach or intestinal cramps at this time. Both may be uncomfortable or painful.
Prostaglandins are also involved in many other PMS symptoms, including headaches.
Progesterone is another hormone that increases right before a menstrual period. For some, progesterone can affect the gastrointestinal tract to cause either constipation or diarrhea.
In females who have chronic bowel issues or an irritable bowel disorder (IBD), such as ulcerative colitis or Crohn’s disease, menstruation can make symptoms worse.
For example, in people with IBD-related constipation, progesterone-associated changes can make constipation worse. This is also true for people with conditions such as endometriosis, uterine fibroids, and ovarian cysts.
Furthermore, people with IBD are more likely to experience other PMS symptoms, such as headaches or menstrual pain.
Progesterone may increase feelings of hunger and can cause cravings for foods high in fat or sugar, such as ice cream or chocolate. The body has a hard time digesting these foods, and eating more of them can affect a person’s bowel movements.
PMS-related changes in dietary habits may contribute to why some people notice differences in the consistency, regularity, or smell of their stool before or during a period.
Increased stress or anxiety
According to research appearing in the journal BMC Women’s Health, people report greater sensitivity to pain and discomfort in the premenstrual phase as well as on their periods. This sensitivity can exacerbate symptoms, too.
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