What parents need to know about strain specificity, timing and why not all probiotics are equal
Medically Reviewed by Bahee Van de Bor, RD, BCAPSc PGDipDiet, Specialist Paediatric Dietitian, former specialist dietitian at Great Ormond Street Hospital, with over 20 years of clinical experience in paediatric digestive health.
Here’s what most parents never hear: not all probiotics work in the same way. The strain matters enormously. And so does the point at which you give it.
When a child has diarrhoea that will not settle, probiotics are usually one of the first things parents reach for.
You’ll find them in every pharmacy, and other parents recommend them in parenting forums.
They feel like a safe, natural thing to try while you are waiting for the GP appointment or wondering what else you can do.
A probiotic that has good evidence behind it, given at the right stage, can genuinely help.
A probiotic without evidence, or given at the wrong time, is unlikely to make any difference and may give you a false sense that you are doing something useful while the underlying issue continues.
The biggest probiotic myth
Many parents assume all probiotics work in the same way. They do not.
The evidence is strain-specific.
A probiotic that helps prevent antibiotic-associated diarrhoea may have no effect on post-infectious symptoms or IBS-type tummy pain.
The strain matters.
Why not all probiotics work for diarrhoea
Probiotics are live microorganisms that, when given in adequate amounts, can support gut health.
But the word probiotic covers thousands of different strains, and strains behave very differently from one another inside the gut.
A useful analogy is antibiotics.
You would not expect a penicillin prescription to treat a urinary tract infection; your doctor has to match the antibiotic to the infection.
Probiotics work in a similar way.
A strain that reduces antibiotic-associated diarrhoea may have no effect on post-infectious loose stools. A strain that supports infant gut health may be irrelevant for a school-aged child with IBS-type symptoms.
This is why buying a general children’s probiotic from a supermarket shelf and hoping for the best is unlikely to move the needle. The evidence for probiotics in children is strain-specific, not category-wide.
Which probiotic strains have evidence for diarrhoea in children?
For diarrhoea in children, the strongest evidence currently supports two strains.
Lactobacillus rhamnosus GG (LGG)
LGG is the most extensively studied probiotic strain in children.
A systematic review combining data from eleven randomised controlled trials found that LGG was effective in reducing the duration of diarrhoea in children when used at an adequate daily dose.
The European Society for Paediatric Gastroenterology, Hepatology and Nutrition concluded that clinicians can consider LGG as an adjunct to rehydration therapy in children with acute infectious diarrhoea.
LGG also has evidence supporting its use in children with IBS.
Multiple randomised controlled trials and a meta-analysis have shown reductions in abdominal pain frequency and intensity.
Rome V cites this strain as having RCT data to support its use in paediatric IBS, and the ESPGHAN/NASPGHAN 2025 guidelines include it as a suggested option.
It comes in a number of formats suitable for children of different ages, including powders you can mix into food or drink.
Saccharomyces boulardii
Saccharomyces boulardii is not a bacterium but a yeast-based probiotic, which makes it particularly useful because antibiotics do not affect it.
Randomised controlled trial evidence supports its use in reducing the duration of acute diarrhoea in children and in reducing the risk of diarrhoea continuing beyond day three of illness.
One practical consideration for parents is that Saccharomyces boulardii is often available in capsule form, and capsule sizes vary significantly between brands.
For younger children who cannot swallow capsules, this can be a barrier.
Some brands offer smaller capsules or sachets.
It is worth checking before purchasing, or asking a paediatric dietitian for guidance on which format is most practical for your child’s age.
When probiotics are most likely to help
The evidence for probiotics in children with diarrhoea is strongest in two specific situations.
During or after a stomach bug
LGG and Saccharomyces boulardii both have evidence supporting their use alongside oral rehydration therapy during acute gastroenteritis.
Starting early, during the acute phase rather than weeks later, appears to give the best results in terms of reducing how long diarrhoea lasts.
In children, a small number of specific strains have paediatric trial evidence showing they can reduce both the risk and duration of antibiotic-associated diarrhoea. The two with the strongest evidence are LGG and Saccharomyces boulardii.
Some adult research has suggested that certain probiotic formulations may delay natural microbiome recovery after antibiotics.
This is a good example of why adult research cannot simply be applied to children.
The paediatric evidence tells a different story. Specific strains given at the right time have been shown to be both safe and beneficial in children taking antibiotics.
The important point is that probiotics are not interchangeable.
The strain, dose and clinical situation all matter.
Because Saccharomyces boulardii is a yeast rather than a bacterium, it is not destroyed by antibiotic treatment and can be taken alongside the course without being affected.
If you are considering a probiotic during antibiotic treatment, speak to a paediatric dietitian about which strain and timing is most appropriate for your child.
When probiotics are unlikely to be enough
This is the part that is rarely explained clearly online, and it matters.
If your child’s diarrhoea started after a stomach bug and has continued for weeks or months, a probiotic alone is unlikely to resolve it.
Post-infectious diarrhoea that persists beyond the acute phase is usually not simply a microbiome imbalance that a probiotic can correct.
As I explain in my post on why some children never seem to recover after a stomach bug, the gut may have become more sensitive overall, food may be moving through differently, or the gut-brain connection may be amplified in ways that a probiotic cannot address on its own.
In these situations, giving a probiotic is not wrong; but it is rarely sufficient.
The underlying pattern needs to be identified first.
A probiotic introduced without that assessment may provide some short-term benefit, or none at all, but it will not resolve the root cause.
Similarly, if your child has IBS-type symptoms, a probiotic may be one useful tool within a structured approach; but it is not a standalone fix.
The sequencing matters. In my clinical work, I assess whether a probiotic is appropriate, which strain is most relevant, and at what point in the management plan to introduce it.
That decision is different for every child.
The intervention is not always the problem. The sequence is.
Is your child still not right after a stomach bug?
Download the free guide and find out why some children don’t bounce back and what actually helps.
What about other probiotic strains?
The market is full of probiotic products making bold claims.
Multi-strain probiotics, high-dose supplements, and brand-name formulations are widely promoted as superior options.
The evidence does not support this. In paediatric IBS and diarrhoea, the evidence base is strain-specific, and for diarrhoea in children, the strongest evidence currently supports LGG and Saccharomyces boulardii.
Other strains may have promising early data but lack the robust randomised controlled trial evidence needed to make a confident clinical recommendation.
VSL#3, a multi-strain probiotic, showed benefit in one paediatric IBS trial; but the original bacterial formulation used in that trial is no longer commercially available in the UK.
Products currently sold under the VSL#3 name cannot be assumed to have the same effect.
This is not to say that the new formulation of strains are harmful.
But parents spending significant amounts on premium multi-strain products on the basis of marketing claims, rather than clinical evidence, are unlikely to see results that reflect the price they are paying.
Looking for exact brand recommendations?
If you want specific brand recommendations for LGG and Saccharomyces boulardii products suitable for children of different ages, including guidance on dose, format and where to buy them in the UK, you will find these in my Probiotics for Thriving Kids Playbook.
This blog helps you understand the evidence. The playbook helps you choose the right product.
When to seek further support
It is worth speaking to a specialist paediatric dietitian if:
- Your child’s diarrhoea has continued for four weeks or more despite trying a probiotic
- You are unsure which strain or format is most appropriate for your child’s age and presentation
- Symptoms began after a stomach bug and have not settled despite dietary adjustments
- Your child has IBS-type symptoms and you want a structured approach rather than trial and error
- You have been told tests are normal but symptoms continue
What structured support looks like
In my clinical programme, the Happy Belly Club®, I work with families through a structured 12-week process.
Before any probiotic or dietary intervention is recommended, I look at the full picture; stool patterns, dietary intake, gut history, symptom triggers, and what has already been tried. That assessment determines whether a probiotic is appropriate, which strain to use, and at what point to introduce it alongside other dietary and gut support strategies.
If you would like to understand whether this approach is right for your child, you can book a free 15-minute Discovery Call. No pressure. Just a clear conversation about what is going on and whether I can help.
Frequently Asked Questions
Some specific probiotic strains have good evidence supporting their use in children with diarrhoea. For diarrhoea in children, the strongest evidence currently supports Lactobacillus rhamnosus GG and Saccharomyces boulardii. However the evidence is strain-specific; a general children’s probiotic without evidence behind that particular strain is unlikely to produce the same results.
LGG and Saccharomyces boulardii both have evidence supporting their use during and after acute gastroenteritis in children. LGG is available in powder form suitable for younger children. Saccharomyces boulardii is often available in capsule form; capsule size varies between brands and may be a practical consideration for younger children who cannot swallow capsules easily.
In children, LGG and Saccharomyces boulardii have been shown to reduce both the risk and duration of antibiotic-associated diarrhoea. Because Saccharomyces boulardii is a yeast, it is not destroyed by antibiotic treatment and can be taken alongside the course. Speak to a paediatric dietitian about which strain and timing is most appropriate for your child.
If diarrhoea has continued for weeks or months despite trying a probiotic, the underlying pattern is likely more complex than a simple microbiome imbalance. Post-infectious gut sensitivity, altered gut motility, or IBS-type symptoms may be contributing; none of which a probiotic alone can address. A structured assessment by a paediatric dietitian can help identify what is actually driving the symptoms.
Not necessarily. In paediatric IBS and diarrhoea, the evidence is strain-specific rather than dose or strain-number dependent. The strains with the strongest clinical evidence for diarrhoea in children are LGG and Saccharomyces boulardii. Multi-strain products may be marketed as superior but the evidence base does not currently support that claim in children.
About the Author
Bahee Van de Bor is a Registered Paediatric Dietitian specialising in children’s digestive health. She has over 20 years of clinical experience, including 12 years working at Great Ormond Street Hospital. Bahee works with families whose children experience constipation, diarrhoea, tummy pain and IBS-type symptoms through her clinical programme, the Happy Belly Club®.
If you are concerned about your child’s ongoing gut symptoms, you can learn more about the Happy Belly Club® or request a Discovery Call to discuss your child’s situation.
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