Tiredness, cramps, low mood and, er… diarrhoea? Yep, it probably wasn’t something you ate, but just another wonderful symptom of the non-stop party that is your period (yay!).

And it’s not just diarrhoea before you come on – you may have noticed other wonderful bowel-related issues such as constipation and bloating appear like clockwork throughout the month. It’s all because the hormones driving our menstrual cycle affect our gut more than you may realise.

Don’t be squeamish – identifying period poo the next time you’re on the loo is the next step in the journey to understanding your menstrual health and the health of your gut. 

“A change in the consistency, frequency and smell of your stool during your period is very common,” explains Dr Elise Dallas, clinical lead for the women’s health team at Babylon.

“[That’s] due to the hormones which fluctuate throughout your menstrual cycle. Receptors lining the gut wall sense and react to these hormones.” In a nutshell, oestrogen and progesterone are believed to slow down movement in the gut. When they peak, that’s when you are most likely to experience constipation or bloating. 

Diarrhoea is more likely just before your period

In the days before your period, if an egg is not fertilised, oestrogen and progesterone levels drop rapidly and another hormone rises – prostaglandin. “Prostaglandins stimulate the uterus to contract and shed its lining, causing your period. But they also do the same to the gut muscles – and this can cause your gut to contract, which may result in cramping and diarrhoea,” says Dr Dallas. Hence, one reason why you may experience a runny tummy just as your period begins.

During ovulation, constipation is more common 

Dr Adiele Hoffman, GP and medical advisor for Flo Health, tells Stylist: “There’s some evidence that oestrogen can affect the gut and cause it to absorb more water and salt from the poop travelling through it, making for harder stools that are more difficult to pass. So some women experience constipation when oestrogen peaks around ovulation.”

Serotonin plays a key role in gut health

When oestrogen levels fall (after ovulation and again at the end of your cycle) it affects levels of serotonin. “You might know it best for its mood-boosting properties, but serotonin also plays a part in the gut,” explains Dr Hoffman.

“There are at least seven different types of serotonin receptors in the gut, and your bowel movements will depend on which ones are activated. Some will speed things up, creating looser and potentially more frequent stools. Others will slow things down, triggering constipation and bloating.”

Dr Hoffman adds that the type and the severity of bowel movement changes will vary from person to person. She highlights a study published in BMC Women’s Health which asked 156 women to fill in the delightful sounding premenstrual ‘poop and pain diary’. 24% of women documented diarrhoea before their period while 28% noticed loosened bowels during menstruation. Constipation, on the other hand, was experienced by 15% before and 10% during their period.

“While these changes can cause discomfort, the good news is that any and all of these symptoms are a normal reaction to changes in your body,” she assures us. 

All our experts said that while temporary changes are usually nothing to worry about, any severe or persistent changes could indicate an underlying problem. They recommend that if you notice anything unusual such as blood in your stools, unexplained weight loss, or a swelling or lump in your gut, you should consult a medical professional. 

IBS and period symptoms

If you have IBS or another inflammatory bowel syndrome, you may notice flare-ups at certain times of the month. This is thought to be down to oestrogen affecting gut sensitivity.

The Lantern’s Clinic’s Dr Margarita Kitova-John, an ex-NHS GP, explains: “Those that suffer from IBS and inflammatory bowel disease are more likely to experience a deterioration of symptoms. Clinical studies have demonstrated that symptoms of IBS become more prominent during menstrual periods, probably due to the peaks and troughs of sex hormones.

“One third of healthy women may experience gastrointestinal symptoms such as bloating and change of stool consistency during their menstrual cycle,” she adds, explaining that around half of women with IBS report a worsening of those symptoms during their period. 

While you can’t expect to maintain ‘optimal poo’ throughout the month, you can help relieve some of the most uncomfortable bowel issues and painful period symptoms by living a gut-healthy lifestyle.

“Cyclical changes in the gut microbiome can affect oestrogen levels in the bloodstream because your gut health and microbial diversity affect how well your gut excretes or recirculates oestrogen,” explains Dr Dallas.

“If the microbiome is not balanced, this can lead to an imbalance in hormones. Having too much oestrogen in the body can lead to gut-related issues like bloating, cramps and fluid retention, and also to symptoms such as mood swings and heavier periods.” 

Optimal gut health positively impacts so much of our physical and mental health, not least your bowels and periods. Tweaking your diet around your menstrual cycle could do wonders for relieving the worst symptoms.

Dr Dallas recommends you stay hydrated and eat a variety of whole foods for a diverse microbiome, aiming for 30 different types of plants a week. “This isn’t as hard as it sounds and includes nuts and seeds,” she says. 

If you manage to eat those 30 plants, you’ll automatically increase your daily intake of fibre – which is especially important around the times you anticipate constipation. “You should eat at least 18-30g of fibre a day,” says Dr Dallas. “Some people find cereals and grains bring on bloating and IBS – if that’s the case, get your fibre from fruit and vegetables instead.”

When you’re experiencing looser stools and diarrhoea, Dr Hoffman suggests you should limit food and drink that causes further aggravation to the bowels: “This includes spicy food, caffeine and artificial sweeteners, which can all trigger the bowels to move faster and are therefore best avoided.

“Try medication, like ibuprofen, which decreases prostaglandins. If you take it for period cramps, you may also notice that it helps with loose stools. However, this might not be suitable for everyone so check with your doctor or pharmacist first,” she adds. 

All menstrual cycles vary from woman to woman, and month to month, and not all women will experience these changes. This is based on a typical 28-day cycle and is approximate.

Days 1-7: Your period

During the early follicular phase while you menstruate, levels of oestrogen and progesterone are low – this increases the speed at which food moves through your gut, and you don’t reabsorb water and nutrients as quickly. Also, prostaglandins are high which relaxes the smooth muscle of your digestive tract, which can also cause diarrhoea.

Poo to expect: looser stools; diarrhoea.

Days 8-13: Follicular phase (latter)

In the later stages of the follicular phase, oestrogen steadily rises; progesterone is increasing slowly (preparing the body for pregnancy) but remains low.

Poo to expect: ‘baseline poo’, ie a healthy, standard stool.

Day 14: Ovulation

Oestrogen peaks around this time which slows the gut, plus progesterone increases which also causes bloating, gas and constipation.

Poo to expect: harder stools; constipation.

Days 15-24: Luteal phase (early to mid)

Progesterone rises and dominates during this phase. Meanwhile, oestrogen levels drop after ovulation but then slowly rise, along with progesterone – this peaks around days 22-24.

Poo to expect: constipation; bloating

Days 25-28: Luteal phase (late)

If an egg is not fertilised, both progesterone and oestrogen levels drop rapidly. This can bring on temporary diarrhoea as the hormones responsible for slowing down the gut suddenly disappear. Prostaglandins rise to help the uterus shed its lining, and subsequently cause the intestines to contract.

Poo to expect: loose stools; diarrhoea 

Images: Getty