Probiotic supplements containing more than one strain of bacteria are commonly referred to as 'multi-strain' supplements, or sometimes as 'poly-strain' or 'polybiotics'. Generally speaking, a multi-strain probiotic can be a good option as an everyday supplement to support gut health. Most high-quality, multi-strain probiotics contain around 5 or 6 different strains, but why not 10 or 15 strains? In theory, you would think that the more strains a supplement has, the better, but this is not necessarily the case.
S. boulardii has been well-researched for diarrhoea
In practice, rather than being beneficial, having 10-20 different strains in one supplement carries various uncertainties. When it comes to probiotics, the question of survival is a key consideration, and when one product contains many strains, it is difficult to establish whether all of the strains will survive until the time of consumption or date of expiry.
Therefore, if you are considering a probiotic supplement with a large number of different strains, make sure tests have been conducted to ensure the strains all survive together at the stated billions count for the duration of its shelf life.
Dr Lynne McFarland from the University of Seattle has authored over 150 peer-reviews, and has concluded from current data that adding more strains doesn't always lead to better outcomes for all illnesses1. But, she also acknowledges that:
'...the benefits of multi-strain mixtures may include broader range of effects and more mechanisms of action…'
There are clearly pros and cons for both single and multi-strain probiotics – the former being more stable, the latter having the potential to offer more benefits, dependent on the strains used and condition being targeted.
Some of the most popular probiotic strains on the market only contain one strain. These are known as 'single-strain probiotics'. Saccharomyces boulardii on its own, for example, can be a great option for supporting people with IBS-D, and research has indicated that sometimes single-strain probiotics have been associated with better results than multi-strain probiotics. When dealing with Helicobacter pylori, for example, using a single strain leads to a 0.66 day reduction in diarrhoea, whilst a two-strain mix leads to a 0.41 day reduction. In this instance, the single strain was more effective.
But, importantly, Dr. McFarland considers that "these are both significant reductions".
A study2 published in 2010 randomly assigned children with rotavirus to receive one of three treatments: oral rehydration therapy plus placebo; oral rehydration solution plus Saccharomyces boulardii, or oral rehydration solution plus a multi-strain probiotic containing Saccharomyces boulardii in combination with Lactobacillus acidophilus, L. rhamnosus, and Bifidobacterium longum.
Both probiotic products decreased the duration of diarrhoea compared to oral rehydration solution alone, but those in the single strain S. boulardii group also saw a reduction in the duration of the associated fever. It is worth noting, however, that those in the multi-strain probiotic group did not experience vomiting symptoms.
The other consideration when choosing a probiotic is that many probiotic supplements are formulated to target specific health conditions3. Based on scientific studies and clinical trials, it is possible to create quality supplements tailored to specific needs. Therefore, instead of adopting a 'more the merrier' approach and opting for a supplement containing a large number of strains, it can be much more important to find a product containing strains which have been researched for the condition you are trying to support. If you are interested in this subject, you can read more about strain-specificity and its importance, over in the Probiotics Learning Lab.
Just like the gut, the vagina also has a microbiome made up of a variety of different micro-organisms, some of which are beneficial and some of which may disrupt the natural balance or cause infections. The homeostasis of the vaginal microbiome requires a prevalence of beneficial bacteria to compete against pathogenic bacteria that can lead to common vaginal infections.
When trying to support vaginal health, it is therefore necessary to use probiotic supplements containing strains of bacteria which are natural residents of the vagina, and which have been researched for the support of vaginal health.
Lactobacillus rhamnosus GR-1® and Lactobacillus reuteri RC-14® are two good examples. A study4 published in 2003 found that use of a probiotic containing these two strains increased levels of friendly lactobacilli in the vaginal microbiome, and decreased levels of potentially pathogenic yeast strains.
Probiotics can be an excellent way to re-balance the vaginal microbiome
For the purposes of this study, 64 healthy women were randomised to be given either oral capsules of Lactobacillus rhamnosus GR-1® and Lactobacillus fermentum RC-14®, or a placebo, once daily for 60 days. They were analysed to determine alterations in pathogenic load and overall changes in gut bacteria profiles.
Results from the study showed an overall increase in the lactobacilli and a decrease in yeast counts in those taking the probiotic compared with the placebo. By day 28, lactobacilli were detected in more women in the lactobacilli-treated group than in the placebo group, and levels of pathogenic E. coli were decreased. Checks at days 60 and 90 confirmed a significant reduction in coliforms.
Another study5 looking at the influence of two single strains on results of on genitourinary dysbiosis found that vaginal flora was normalised in patients suffering from vaginal infections following probiotic intervention.
The study looked at 250 women suffering from vaginal itching, burning, and itching, of which 125 took a probiotic containing Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 alongside medication, and 125 took the medication only. After 6 weeks, inflammation had decreased, lactobacilli numbers had increased, and pathogenic microorganisms were lower in the group treated with probiotics.
The two-strain probiotic containing Lactobacillus rhamnosus GR-1® and Lactobacillus reuteri RC-14® was effective at reducing pathogenic load, modulating host immunity, and maintaining a normal healthy vaginal flora.
The probiotic increased levels of lactobacilli bacteria which are needed to maintain a healthy vaginal microbiome, and displaced less beneficial strains, thus reducing overall dysbiosis within the urinary tract. A good probiotic supplement will encourage other beneficial species and strains to thrive and influence the microbiome as a whole rather than just topping up existing bacterial populations or dominating the microbiome with one or two strains.
It's more important to have fewer high-quality strains that are specific to your condition, than lots of different strains
Using specific strains can provide a more targeted and effective approach to gut health, but the synergy between multi-strain combinations, and the broader range of effects they may provide when used together, needs more research.Strain-specific probiotic therapy can certainly provide benefits for specific conditions, but as you can see there are no universal rules - for some individuals taking a single-strain probiotic like Saccharomyces boulardii works well, whilst for others a dual or multi-strain probiotic might be better. The quality of the probiotics strains used is by far the most important factor to consider when selecting the right supplement, and looking at the available clinical trials behind the strains will help you to select the right strain (or strains) for you or your clients.
For further reading on the topic, take a look at 'The Numbers Myth', over in the Probiotics Learning Lab.
1. Scattergood, G. (2017). 'Multi-strain versus single strain probiotics: More doesn’t necessarily mean better outcomes'. Published online. Available at: https://www.nutraingredients.com/Article/2017/10/19/Multi-strain-versus-single-strain-probiotics-More-doesn-t-necessarily-mean-better-outcomes
2. Grandy, G et al. (2010) Probiotics in the treatment of acute rotavirus diarrhoea. A randomized, double-blind, controlled trial using two different probiotic preparations in Bolivian children. BMC Infect Dis, 10: 253
3. Verna, E. and Lucak, S. (2010) 'Use of probiotics in gastrointestinal disorders: what to recommend?' Therap Adv Gastroenterol, 3(5): 307-319
4. Reid, G et al (2003) ‘Oral use of Lactobacillus rhamnosus GR-1 andL. fermentum RC-14 significantly alters vaginal flora: randomized, placebo-controlled trial in 64 healthy women.’ FEMS Immunology and Medical Microbiology 35. pp. 131-134
5. Perišić Ž, et al. (2011) ‘The influence of probiotics on the cervical malignancy diagnostics quality’, Vojnosanit Pregl. Vol 68(11 ): pp. 956–960.
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