Probiotic science has evolved, and the idea that all live bacteria supplements have similar effects, and that you should take one daily for your general health is outdated. This explains why, despite 48% of adults having taken a live bacteria supplement, 77% have noticed no significant health benefits, according to a recent survey of 2000 UK consumers. Just as you wouldn’t take an iron supplement to address a vitamin D deficiency, the latest gut microbiome science tells us how important it is to get specific – we should be taking the right strain, at the right time, in the right way.
With so many live bacterial supplements available today (often referred to as ‘probiotics’) - most of which are not backed by human scientific studies - navigating through the choice on offer can feel like a minefield. In fact, almost three-quarters of regular probiotic users admit they find it difficult to choose the right live bacteria supplement, with only one in ten reporting they feel very confident in their selection.
This guide will help you understand what a bacterial strain actually is, why that matters, and how to choose the right one for you.
Why bacterial ‘strains’ matter
Each individual type of bacteria belongs to a genus, species and strain, and has a specific purpose. The scientific community and World-leading health authorities - including the World Gastroenterology Organisation (WGO) and the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHN) - agree that, to have a real impact, each strain should be taken for a specific reason, at a specific dose, and in a specific format, supported by high quality human studies. In other words: taking the right strain, at the right time, in the right way.
Here's an illustration to help you understand the importance of identifying the right strain to suit your requirements:
In this visual example, each bacterial strain is compared to a breed of dog, and just as you’d expect a Chihuahua to have very different qualities and behaviours compared to a Rottweiler, different strains will also have varying qualities and will act very differently from each other.
That’s why it’s essential to pay attention to the specific strain - not just the species - as only certain strains have been proven effective in placebo-controlled human studies for specific needs (for example, when you’re on antibiotics, LGG is recommended by the WGO guidelines on probiotics). Think of it this way: selecting your live bacterial supplement by species rather than by strain is like choosing a lion instead of a dog — they may both be mammals, but they’re completely different and serve a very different purpose!
SMART tip: Check the strain(s) - not just the species - on your live bacterial supplement and make sure there are placebo-controlled human studies to support their use for your specific needs e.g. right strain, right time. If you’re unsure, you can always ask the company you’re buying from, or do your own research if you’re into the science like us.
‘More’ doesn’t always mean ‘better’
Despite what you may have heard, ‘more’ strains or ‘more’ billions of bacteria doesn’t equate to a better product. Here’s why…
More strains: It’s important to ensure that any bacterial strains clumped together in a single product have been tested and scientifically proven to work together in human studies. To come back to the animal example, you certainly wouldn’t mix a lion and a zebra at a species level, and you wouldn’t leave a chihuahua with a rottweiler without testing their relationship first. In the same way, live bacterial supplements should not mix different strains that haven’t been tested together, as they can compete against each other (making them ineffective).
More billions: Dosage matters but ‘more’ doesn’t always mean better. What’s important is to choose the right dose that has been tested and proven effective in human studies for your needs, replicating the formulation and format used in those studies, for the best results.
SMART tip: Check that the strain (or combination of strains) in your live bacterial supplement have been proven to work together in human studies, and that the dose (eg. bacterial count) matches that used in those studies. Again, if you’re unsure, always ask the company you’re buying from.
Never compromise on quality
Unsurprisingly, a top priority when choosing a live bacterial supplement is to ensure it’s both safe and effective. For the supplement to have a real impact, its microbes need to remain alive and viable throughout its shelf life.
Environmental factors such as temperature, humidity, exposure to light, certain foods or drinks can all impact their survival, either on shelf, or once consumed. A high quality live bacterial supplement will always consider these factors and dictate the right way to take and store the product.
And that’s not all. Once ingested, the bacterial cultures must be proven in scientific studies to reach their destination alive (whether that’s the gut, vagina or other microbiome), and to survive and thrive in their intended destination, to be effective.
SMART tip: Look for products that guarantee the number of bacteria at the end of the product’s shelf life, not just at the time of manufacture (the scientific unit of measure for bacteria is colony-forming units aka ‘CFU’, just like liquid is measured in millilitres – bacteria are measured in CFUs). Check the strains have been scientifically proven to reach their destination alive and check that the instructions on how to store and take the product are available and clear.
Avoid unwanted hidden ingredients
It might surprise you to learn that many live bacterial supplements available today include an array of food additives, such as emulsifiers, even in products intended for babies. Emerging research (including new, emerging research from Megan’s team at King’s College London) suggests that certain food additives, including artificial sweeteners and emulsifiers - commonly found in ultra-processed foods (UPFs) and supplements - may have a negative impact of the gut microbiome.
More specifically, early findings indicate that certain emulsifiers may disrupt the balance of gut bacteria in those who are genetically susceptible, potentially leading to increased inflammation and weakening of the protective mucus lining of the gut, making it easier for ‘unfriendly’ bacteria to thrive. While human studies are ongoing, it’s worth limiting unnecessary additives in UPFs and supplements seeking out alternatives, where possible.
SMART Tip: Double check the full list of ingredients in your live bacterial supplement, and make sure there are no unwanted / hidden food additives. These include added sugars, emulsifiers, sweeteners, flavours or preservatives.
Conclusion
The idea that you can take a daily probiotic for generalised gut health is outdated. Instead, the latest science - and international probiotic guidelines - emphasise the importance of taking the right strain, at the right time, in the right way. By focusing on evidence-based solutions, we can navigate this space more effectively and support better outcomes.
Sources:
● Data on File, 2025. Research by Opinium on behalf of SMART STRAINS® 2,000 Nationally Representative UK Respondents, aged 18+ 03.01.2025-06.01.2025
● NHS. Probiotics. https://www.nhs.uk/conditions/probiotics/
● British Dietetic Association (BDA). (n.d.) Probiotics. Available at: https://www.bda.uk.com/resource/probiotics.html
● ISAPP Science. (n.d.) Resources: Probiotics. Available at: https://isappscience.org/for-scientists/resources/probiotics/
● National Institutes of Health (NIH). (n.d.) Probiotics: Health Professional Fact Sheet. Available at: https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/
● Whelan K. et al Nat Rev Gastroenterol Hepatol. 2024 Jun;21(6):406-427. https://pubmed.ncbi.nlm.nih.gov/38388570/
● Naimi S. Microbiome. 2021 Mar 22;9(1):66. https://pubmed.ncbi.nlm.nih.gov/33752754/
Written by Rachel Redman - Registered Dietitian
Reviewed by Dr Megan Rossi - Leading dietitian with award-winning PhD in probiotics.