Many people take probiotics to improve their bowel habits – usually due to constipation or diarrhoea – but do they work?
In this article, we look at the research and explain the science behind probiotics and how they might influence stool frequency and consistency.
We also discuss probiotics’ potential use for people with irritable bowel syndrome (IBS) and outline some of their other possible benefits.
What are probiotics?
Probiotics are live, friendly microorganisms that can support your gut health if you consume them in sufficient amounts.
Most often, commercially available probiotics contain live bacteria, and they’re available in a range of forms, including capsules, pills and liquids.
How do they work?
Your gut is filled with bacteria and other microbes, collectively called the gut microbiome. When this community of microbes is diverse and thriving, it supports not just the health of your gut, but the health of your whole body.
Gut bacteria achieve this in many ways. For instance, they aid digestion by breaking down nutrients, like fibre and plant chemicals. They also produce healthy compounds, such as short-chain fatty acids (SCFAs).
In addition, gut bacteria keep your immune system in tip-top condition, which can influence the activity of different immune cells.
In short, probiotics help support your gut microbiome, and they likely do this in a number of ways, including:
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helping to maintain balance by inhibiting pathogenic, or ‘unfriendly’, microbes in the gut
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producing healthy compounds, like SCFAs
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supporting your immune system
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synthesizing vitamins
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strengthening your gut barrier
Common probiotic strains
There’s a wide range of probiotics available. Some products contain just one species, while others provide a number of species, and these may include:
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Bifidobacterium:
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B. animalis
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B. adolescentis
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B. breve
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B. bifidum
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B. longum
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Lactobacillus:
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L. acidophilus
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L. gasseri
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L. casei
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L. johnsonii
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L. fermentum paracasei
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L. rhamnosus
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L. plantarum
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L. salivarius
What about fermented foods?
Fermented foods, like kombucha, kefir and sauerkraut, are healthy additions to your diet. Although some do contain live microbes, technically, these foods aren’t classed as probiotics.
To be considered a probiotic, a product must contain live microbes and have health benefits when consumed in sufficient amounts.
Can probiotics change your bowel habits?
For some people, probiotics do change the frequency and consistency of their stool. It may not be the same for everyone, but evidence suggests that probiotics can ease diarrhoea and constipation in some cases.
We’ll cover some of the evidence for these benefits in the sections below.
It’s worth noting that if your bowel movements are already healthy and stress-free, you may not notice any changes. But first, the basics.
How often should you poo?
In general, if you poo anywhere from three times each day to three times each week, experts consider that normal.
If you’d like to know about the ‘ideal’ consistency of poo, take a look at the Bristol stool chart.
Probiotics and diarrhoea
Having diarrhoea means that you’re frequently passing loose, watery poos. It can be caused by a number of factors, including food poisoning and certain medications.
There’s evidence that probiotics may:
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prevent diarrhoea caused by Clostridium difficile, a serious gut infection
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relieve acute infectious diarrhoea, which is also called gastroenteritis or stomach flu
Because the root cause can vary, make sure you speak with a doctor if your diarrhoea doesn’t clear up within 1 week or is particularly severe.
Probiotics and constipation
If you’ve done fewer than three poos in a week, your poos are hard or lumpy, or they’re hard to pass, you might be constipated.
As with diarrhoea, a number of factors might be the cause, including dehydration, not eating enough fibre or not getting enough physical activity.
Thankfully, there’s some evidence that probiotics can offer relief. For instance, the new 2025 British Dietetic Association guidelines for constipation summarise the current evidence on probiotics’ use.
The guidelines conclude that probiotics can improve:
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constipation symptoms overall: the collection of common symptoms
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stool frequency: how often you poo
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stool consistency: how hard your stool is
There’s also some specific evidence that probiotics can improve constipation in older adults – an age range when constipation is common.
If you’re struggling with constipation, we have an article that includes tips to help get things moving.
And if your constipation doesn’t ease up after treatment, it keeps coming back or you lose weight without trying, speak with your doctor.
Probiotics and IBS
IBS is a common gut condition that causes symptoms including stomach cramps and bloating. It’s often accompanied by diarrhoea, constipation or both.
Interestingly, there’s growing evidence that probiotics may help ease diarrhoea and constipation in people with IBS.
For instance, a 2024 systematic review of eight studies found that ‘All eight trials came to the same conclusion: probiotic treatment may significantly reduce symptoms’.
If you want to try a probiotic for your IBS, it’s best to take it for up to 12 weeks and monitor your symptoms. If you don’t notice any improvements, stop taking it.
There are many approaches to managing IBS, and different approaches work for different people.
Are there any other benefits to probiotics?
While some people take probiotics to improve their stool habits, there are other potential benefits, including:
For more information about probiotics and how they can support overall health, read this next.
FAQs
Here are some common questions about probiotics and poo.
Is looser poo normal when I start probiotics?
Because everyone’s gut is different, we all respond slightly differently to probiotics. Some people may have looser stools initially. Others may not notice any changes at all.
How often should I poo?
The general expert consensus is that pooing anywhere from three times a day to three times a week is normal. If you’re outside of these guidelines, you might have constipation or diarrhoea.
What are the best foods for regularity?
One of the most important dietary strategies for staying regular is to eat more fibre. All plants contain fibre, so aim to up your intake of fruit, vegetables, nuts, seeds and legumes.
Certain foods can be particularly helpful, such as kiwis, prunes, linseeds, rye bread and chia pudding. Also, remember to stay hydrated.
Can probiotics help constipation and diarrhoea?
There is some evidence that, at least for some people, probiotics can ease constipation and diarrhoea.
Summary
Constipation and diarrhoea are common. Often, they’re nothing to worry about, but they can be unpleasant.
There’s evidence to suggest that probiotics can ease some forms of diarrhoea and constipation, although scientists continue to investigate the specifics.
Similarly, there’s growing evidence that probiotics might help reduce symptoms of IBS for some people.
Alongside benefits to stool consistency and frequency, probiotics might also provide benefits beyond the gut, including improvements to sleep, skin and mood.
Importantly, probiotics are generally considered safe, so they’re worth trying if you’re experiencing changes in bowel habits. However, if the changes to your toilet routines persist, speak with a doctor to identify the cause.
To learn more about other gut health topics, visit Symprove’s Gut Hub.
Sources
British Dietetic Association guidelines for the dietary management of chronic constipation in adults. Journal of Human Nutrition and Dietetics. (2025). Link.
Constipation. (2023). Link.
Diarrhoea. (2023). Link.
Effectiveness of probiotic use in alleviating symptoms of irritable bowel syndrome: A systematic review. Cureus. (2024). Link.
Effect of probiotics on depression: A systematic review and meta-analysis of randomized controlled trials. Nutrients. (2016). Link.
Effects of probiotics on cognitive reactivity, mood, and sleep quality. Frontiers in Psychiatry. (2019). Link.
Meta-analysis: Probiotics in antibiotic-associated diarrhoea. Alimentary Pharmacology and Therapeutics. (2012). Link.
Oral and topical probiotics and postbiotics in skincare and dermatological therapy: A concise review. Microorganisms. (2023). Link.
Probiotics for the prevention of antibiotic-associated diarrhoea: A systematic review and meta-analysis. BMJ Open. (2020). Link.
Probiotics for the prevention of Clostridium difficile‐associated diarrhea in adults and children. Cochrane Library. (2013). Link.
Probiotics for treating acute infectious diarrhoea. Cochrane Library. (2010). Link.
The effect of probiotics as a treatment for constipation in elderly people: A systematic review. Archives of Gerontology and Geriatrics. (2017). Link.
The effect of probiotics on functional constipation in adults: A systematic review and meta-analysis of randomized controlled trials. The American Journal of Clinical Nutrition. (2014). Link.
The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology and Hepatology. (2014). Link.
Warding off recurrent yeast and bacterial vaginal infections: Lactoferrin and Lactobacilli. Microorganisms. (2022). Link.
