Written by Shereen, Product Management Associate · Updated 20 October 2026
How does your menstrual cycle affect your gut health?
Your gut follows your hormones, so its changes are predictable and easier to plan for. After ovulation, rising progesterone slows digestion, so bloating and constipation are common before a period. As your period starts, prostaglandins can speed the bowel up, bringing cramps and looser stools. Fibre, fluids, movement and a daily pre+probiotic support a calmer gut all month.
This article is for you if: your digestion changes around your period, with bloating or constipation before it or looser stools during it, and you want to know why and what helps.
If your digestion shifts around your period, you're far from alone. In a survey of 156 healthy women, 73% had at least one gut symptom, such as tummy pain or diarrhoea, in the five days before or during their period. Women who felt low or anxious at that time were more likely to have several gut symptoms at once.[1]
These changes follow your hormones, so they tend to repeat each month. That's good news: once you know the pattern, you can plan for it.
→ See Cycle Harmony Pre+Probiotic Melts, our daily pre+probiotic for your cycle
In this article
- Why do you get diarrhoea on your period?
- Why do you get bloated and constipated before your period?
- How does your gut change in each phase of your cycle?
- What helps your gut during your period?
- Can your gut health affect your menstrual cycle?
- Can you take probiotics during your period?
- Frequently asked questions
Why do you get diarrhoea on your period?
Period diarrhoea comes from prostaglandins, natural compounds released by the womb lining as your period starts. They make the womb contract, and they can also reach the bowel and speed it up.
- When an egg isn't fertilised, oestrogen and progesterone fall and the womb lining leaves the body as your period.[2]
- The start of a period brings a rise in prostaglandins in the womb. These can enter the bloodstream and reach the gut, where they're linked to tummy pain, more frequent bowel movements and diarrhoea. Across studies, diarrhoea is the gut symptom women report most often during their period.[3]
- In the survey of healthy women, 55% had tummy pain and 28% had diarrhoea during their period.[1]
Cramps and looser stools often arrive together, because prostaglandins are linked to both.[3] For the cramping side, our guide to what actually helps period cramps walks through the options.
Why do you get bloated and constipated before your period?
After ovulation, progesterone rises and your gut tends to move more slowly. That slower pace is one reason bloating and constipation are common in the days before a period.
- In the second half of your cycle, progesterone helps the womb lining prepare for a possible pregnancy.[2]
- In a study of 15 women, food took significantly longer to travel from the mouth to the large bowel in the luteal phase (the time between ovulation and your period), when progesterone was high, than in the follicular phase before ovulation.[4] A later review of studies in healthy women also describes slower gut transit in the luteal phase.[3]
- In the five days before a period, 62% of the women surveyed had bloating, 58% had tummy pain and 15% had constipation.[1]
Bloating before a period can have more than one cause. Our guide to why period bloating happens and what eases it looks at each one.
How does your gut change in each phase of your cycle?
Your gut tends to follow a monthly rhythm: quicker in the first half of your cycle, slower after ovulation, and looser again as your next period starts. The days below are for a typical 28-day cycle. Cycles of 21 to 35 days are normal, so shift the days to match yours.[2]
| Phase | What your hormones do | Common gut changes | What helps |
|---|---|---|---|
| Your period (about days 1 to 5) | Oestrogen and progesterone are low. Prostaglandins rise as the lining sheds | Looser, more frequent stools and tummy cramps | Sip fluids through the day, keep meals regular and simple, keep up gentle movement |
| After your period (about days 6 to 14) | Oestrogen rises towards ovulation, around day 14 | Gut transit is quicker than after ovulation | Build your habits: fibre at every meal, 6 to 8 glasses of fluid, 30 minutes of movement |
| After ovulation (about days 15 to 23) | Progesterone rises | Slower gut transit, which can mean constipation | Aim for 25 to 30 g of fibre: brown rice, wholemeal bread, vegetables, kiwi, prunes or dragon fruit |
| The days before your period (about days 24 to 28) | Progesterone and oestrogen fall | Bloating, tummy pain, constipation or looser stools | Keep fibre and fluids up, drink more on hot days, keep a regular toilet routine |
Cycle timings: NHS.[2] Gut changes: studies in healthy women.[1] [3] [4] What helps: HealthHub.[5] [6]
What helps your gut during your period?
Simple daily habits do the most for period gut changes, and they work best when you keep them up all month rather than only in the week of your period.
- Fibre, spread across the day. Aim for about 25 to 30 g of fibre a day.[6] Easy swaps: brown rice instead of white, wholemeal bread instead of white, half your plate as vegetables, and fruit such as kiwi, prunes or dragon fruit.[5]
- Fluids, with extra in the heat. HealthHub suggests 6 to 8 glasses of fluid a day, about 2 litres.[5] You may need more in a hot environment,[7] so on humid Singapore days, or after a sweaty workout, keep a water bottle with you. Barley drink, chrysanthemum tea and soup all count.[5]
- Probiotic foods. Low-sugar yoghurt, live-culture drinks, tempeh and kimchi are easy to add to your week.[5]
- Daily movement. At least 30 minutes of exercise a day helps your digestive system work better.[5]
- A regular toilet routine. Go when you feel the need, and keep a routine for bathroom visits.[5]
- Sleep and calm. Plenty of sleep, regular exercise and relaxing habits such as yoga or meditation are part of the NHS self-help advice for PMS (premenstrual syndrome).[8]
See a doctor if your period pain is severe or stops your usual activities, or if your bowel habits change in a way that doesn't follow your cycle.[9]
Can your gut health affect your menstrual cycle?
Yes, your gut and your hormones influence each other. Hormones change how quickly your gut moves, and your gut bacteria help control how much active oestrogen circulates in your body.
Some gut bacteria make an enzyme called beta-glucuronidase, which turns oestrogen the body has already processed back into its active form, so it can return to the bloodstream. When gut bacteria are less diverse, less oestrogen is reactivated and circulating levels fall. Researchers are studying how this gut and oestrogen link may play a part in conditions such as polycystic ovary syndrome (PCOS) and endometriosis.[10]
This two-way link is a good reason to look after your gut every day of the month, not only in the week of your period. Our guide to cycle syncing your supplements in each phase shows how to match your routine to your cycle.
Can you take probiotics during your period?
Yes. There's no need to pause probiotics during your period, and research on probiotics and period symptoms has used them every day, right through the cycle.
- Probiotics are live microorganisms intended to have health benefits, and they have an extensive history of apparently safe use, particularly in healthy people.[11]
- In a 2026 placebo-controlled trial in Thailand, 48 women aged 18 to 24 with moderate to severe period pain took a daily Lactobacillus and Bifidobacterium probiotic with prebiotics, or a placebo, for three cycles. After three months, average pain scores were 3.7 out of 10 with the probiotic, compared with 5.8 with the placebo. The benefit came with daily use, so consistency matters.[12]
- For regularity, a review of 14 randomised trials with 1,182 adults with constipation found that probiotics shortened gut transit time by 12.4 hours and added 1.3 bowel movements a week, with Bifidobacterium lactis showing the clearest effect.[13]
Cycle Harmony Pre+Probiotic Melts is our daily pre+probiotic for your cycle. Each sachet gives you 10 billion CFU (colony-forming units) of Lactobacillus fermentum, with a 65 mg blend of chaste berry extract, maritime pine extract and inositol. Chaste berry has been studied for PMS: in a placebo-controlled trial of 170 women, a daily chaste berry extract taken over three cycles improved a combined score of symptoms such as irritability, mood changes, headache, breast fullness and bloating, and 52% of women saw their symptoms fall by at least half, compared with 24% on placebo.[14] It's a raspberry-flavoured melt that dissolves on your tongue, no water needed, so it's easy to keep up every day. It contains milk and soy.
If your gut feels unsettled all month, not only around your period, Daily Pre+Probiotic Melts gives you 15 billion CFU of 7 patented probiotic strains with 85 mg of two prebiotics, polydextrose and fructo-oligosaccharides. It's a cranberry-flavoured melt, best taken after meals, and it contains milk.
If you're pregnant, breastfeeding, on medication or have allergies, check with your doctor first.
Shop Cycle Harmony Pre+Probiotic Melts
90-day money back guarantee
Related reading: Period bloating: why it happens and what eases it · What actually helps period cramps? · Cycle syncing your supplements: what to take in each phase
Frequently asked questions
Can probiotics make you start your period?
There's no known way for probiotics to start a period. Your period begins when oestrogen and progesterone fall at the end of your cycle. If yours comes early or late, common reasons include stress, a big change in weight, a lot of intense exercise or hormonal contraception, and a doctor can help if the change continues.
How long should you take a probiotic before you notice a difference?
Studies on probiotics and period symptoms have run for three cycles of daily use, so give a probiotic at least that long before you judge it. Take it every day, not only during your period, so your gut gets steady support across the whole month.
What's the difference between Cycle Harmony Pre+Probiotic Melts and Daily Pre+Probiotic Melts?
Cycle Harmony Pre+Probiotic Melts pairs 10 billion CFU of Lactobacillus fermentum with a 65 mg blend of chaste berry extract, maritime pine extract and inositol, for support across your cycle. Daily Pre+Probiotic Melts is made for everyday digestion, with 15 billion CFU of 7 patented probiotic strains and two prebiotics. Choose Cycle Harmony Pre+Probiotic Melts if your gut changes follow your cycle, and Daily Pre+Probiotic Melts if they happen all month.
Is Cycle Harmony Pre+Probiotic Melts suitable for everyone?
Cycle Harmony Pre+Probiotic Melts contains milk and soy, so avoid it if you're allergic to either. If you're pregnant, breastfeeding, on medication or have a medical condition, check with your doctor before you start.
Key takeaways
- Gut changes around your period are common: 73% of women in one survey had at least one.
- Prostaglandins released as your period starts can speed up the bowel, bringing cramps and looser stools.
- Rising progesterone after ovulation slows gut transit, one reason for bloating and constipation before a period.
- Fibre, 6 to 8 glasses of fluid (more in Singapore's heat) and daily movement help your gut all month.
- You can keep taking probiotics during your period. Research on period symptoms used them every day for three cycles.
About the author: Shereen is a Product Management Associate at The Purest Co. A Master's graduate in Pharmacy from Monash University, she brings four years of research experience to product development, with a focus on evidence-based, thoughtfully formulated supplements that support everyday wellbeing.
References
[1] Bernstein MT et al. Gastrointestinal symptoms before and during menses in healthy women. BMC Womens Health. 2014.
[2] NHS. Fertility in the menstrual cycle. Reviewed 5 January 2023.
[3] Bharadwaj S et al. Symptomatology of irritable bowel syndrome and inflammatory bowel disease during the menstrual cycle. Gastroenterol Rep (Oxf). 2015.
[4] Wald A et al. Gastrointestinal transit: the effect of the menstrual cycle. Gastroenterology. 1981.
[5] HealthHub (Ministry of Health Singapore). Constipation in adults: causes and prevention. Reviewed 19 August 2024.
[6] HealthHub (Pharmaceutical Society of Singapore). Constipation. Reviewed 31 December 2024.
[7] NHS. Water, drinks and your health. Reviewed 17 May 2023.
[8] NHS. PMS (premenstrual syndrome). Reviewed 18 June 2024.
[9] NHS. Period pain. Reviewed 18 March 2026.
[10] Baker JM et al. Estrogen-gut microbiome axis: physiological and clinical implications. Maturitas. 2017.
[11] National Center for Complementary and Integrative Health (NIH). Probiotics: what you need to know. Updated August 2019.
[12] Vallibhakara O et al. Efficacy of probiotic supplementation in reducing primary dysmenorrhea: a double-blinded randomized controlled trial. Sci Rep. 2026.
[13] Dimidi E et al. The effect of probiotics on functional constipation in adults: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 2014.
[14] Schellenberg R. Treatment for the premenstrual syndrome with agnus castus fruit extract: prospective, randomised, placebo controlled study. BMJ. 2001.
These statements have not been evaluated by any regulatory authority. This product is not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary. Consult a healthcare provider before use if you are pregnant, breastfeeding, or on prescribed medication.