When it comes to probiotic strains, is more better?
There is a huge variety of probiotics available that, as well as being delivered in different ways (foods, drinks, supplements), also contain different types and numbers of strains i.e. single-strain (contains one type of microbe) or multi-strain (contains two or more different types of microbes). An assumption some make is that the more strains you have, the more effective the probiotic will be. This may be because individual strains have their own mechanism(s) of action, and so they may assume that combining strains allows for a broader range of mechanisms to be covered. However, these multiple mechanisms may have antagonistic effects and may even reduce the effectiveness of a strain compared to if they had been given in isolation. Previous research has tried to see if the science supports the theory but failed to show a significant difference between single- and multi- strained probiotics.1-3 However, a common limitation to these studies is that they are only grouped by ‘single-‘ or ‘mixed-‘ strains and they don’t account for strain-specific effects.
To help address this, a recent systematic review only included randomised-controlled trials in which there was both at least one trial using a single strain and at least one trial using the same single strain combined within a multi-strain mixture, for the same disease indication.4
Sixty-five trials were included in the analysis, totalling 10,863 participants. The trials included covered eight conditions related to; allergy, gastrointestinal disease, immunity and neonatal health.
In general, no significant effect was identified to suggest that multi-strain probiotics confer a greater effect than that of single-strain probiotics, although there were a few exceptions. The findings from this study highlight that the number of different species appears to be less important and it is in fact about choosing the most appropriate probiotic for the disease indication. For example, Lactobacillus rhamnosus GG alone, but not when combined in a mixture with other strains, had significant effects in necrotising enterocolitis. Furthermore, Lactobacillus rhamnosus GG combined in a two-strain mixture with Bifidobacterium lactis Bb12 had a significant effect in Helicobacter pylori, but when given in isolation or combined in a 4-strain mixture no effect was demonstrated. This reinforces that some combinations of strains may have antagonistic effects.
Although the design of this study is advantageous compared to previous reviews comparing single- and multi- strain probiotics, many commonly used probiotics did not meet the inclusion criteria because the single-strain probiotics haven’t been used in a multi-strain mixture, and vice versa, which minimised the pool of studies that could be included.
Nonetheless, this review concludes that single-strain probiotics are as effective as multi-strain mixtures. When it comes to choosing a probiotic, selecting a strain(s) that has demonstrated efficacy through human intervention trials is the most important factor to consider.
1. Goldenberg et al. (2015) Cochrane Database Syst Rev. 4:CD004827
2. Johnston et al. (2012) Ann Intern Med. 157: 878-888
3. Chang et al. (2017) PLoS ONE 12:e0171579
4. McFarland (2020) Dig Dis Sci DOI:10.1007/s10620-020-06244-z [Epub ahead of print]