Why does my period upset my stomach?

Q: I have diarrhea around the time of my period. Why does this happen, and can I make it stop?

A: About a quarter of healthy women get diarrhea just before their menses, and even more experience loose stools once they start. Researchers suspect this combination is a result of cyclic hormonal changes that can take a toll on the gut.

There are two main reasons. One is progesterone, an important sex hormone released by the ovaries after ovulation. It usually peaks a few days before menses and then drops to low levels until the cycle repeats.

Progesterone helps the uterus lining mature to create a suitable environment for possible egg implantation. But the hormone also relaxes the muscles of the gut, causing food and waste to travel more slowly through your system (the reason many women experience constipation during pregnancy, a time of steadily rising progesterone levels).

When it comes to diarrhea, though, the problem is the drop in progesterone that happens around when the period starts. Low levels of the hormone speed up the bowels to give looser, more frequent stools.

The second reason is hormonelike compounds called prostaglandins, which are produced by nearly every cell in your body. During menses, prostaglandins are released to cause the muscles of the uterus to contract and shed its lining, producing the oft-loathed period cramps. Unfortunately, prostaglandins also affect the muscles of the gut. When those start contracting in overdrive, the result is simultaneous diarrhea.

The pattern and levels of these biological compounds vary person to person, and even month to month. Stool frequency is also heavily influenced by other factors such as diet, water consumption, exercise and stress. This probably accounts for why not everyone experiences bowel changes the same way during their periods. But for those with bad diarrhea, here are some ways to mitigate the situation:

Eat more soluble fiber and drink more water

Soluble fiber such as that found in oats or black beans can remove excess fluid from your stool during digestion, so ramping up the amount of soluble fiber in your diet can combat the diarrhea wrought by your period.

Keep in mind, when you have severe diarrhea, you may quickly become dehydrated, especially when coupled with fluid losses through your menses. It's important to counter this by drinking lots of water and replacing electrolytes if needed ( don't worry, doing so won't aggravate your diarrhea, but it will help replenish your body).

Try over-the-counter medications

If diarrhea, rather than cramping, is the most bothersome symptom for patients, I advise them to first try an alternative medication, loperamide, found in drugs such as Imodium. When taken at recommended doses (usually starting with 4 mg and then 2 mg after each subsequent loose stool, not to exceed 8 mg daily), loperamide specifically slows down the gastrointestinal tract without affecting other organs.

There hasn't been convincing data on probiotics to treat diarrhea during menses - although probiotics have been shown to help with diarrhea caused by infections as well as in irritable bowel syndrome.

Birth control may help

Many women find their periods become lighter, shorter and less painful after starting birth control. Combination oral contraceptives can regulate fluctuations in sex hormones each cycle and thin the endometrium, leading to reduced production of prostaglandins. If trying birth control seems right for you, speak with your physician about your symptoms and options.

Try to reduce stress

There's a strong connection between our mind and bowels, a bidirectional pathway known as the brain- gut axis, that explains why stress can cause bowel symptoms. Starting your period - and all the discomfort that accompanies it - can lead to elevated stress. Mindfulness, meditation and exercise are all simple ways to help boost your mood and relieve extra tension during your period, which can in turn help mitigate your loose stools.

Signs of a more serious problem

For most women, the unwanted diarrhea associated with your period can be eased with a few simple interventions. If you have severe abdominal pain during your menses, experience pain with bowel movements or sexual activity, or notice blood in your stools, it’s important to discuss these symptoms with your physician. They could be signs of a condition called endometriosis in which tissue similar to your uterine lining grows in other parts of your body such as the intestine.