Probiotics are defined as ‘live microorganisms that when administered in adequate amounts confer health benefits on the host’. The potential benefits of probiotics have been well documented, but there is still plenty of confusion about how to evaluate the effectiveness of a probiotic as a consumer, as there are so many factors to consider. We have written about some of these considerations in the past, such as single strains vs. multiple strains, refrigerated vs. unrefrigerated, method of preparation, and what kind of scientific research a company has to prove the effectiveness of their products. Despite the importance of these considerations, the one that most companies have pushed to the forefront is the CFU count. CFUs, or colony forming units, represent the number of live probiotic bacteria that are supposed to be in each serving. Most probiotic companies use this number alone to sell the effectiveness of their products because it’s cheap to increase CFU counts, and it’s an easy talking point for marketing to general consumers. We have already written about misconceptions surrounding CFU counts in the past, but we’re going to revisit that topic today with a research study that dives deeper into the importance of CFU counts.1

How many CFUs do we really need?

In order to know how many CFUs we need, we first need to know why what we’re trying to achieve by taking a probiotic. This study shows that a certain amount of viable cells seem to be necessary to obtain different effects such as strengthening immune functions, competition for nutrients or adhesion sites along the gastrointestinal wall, control of toxin production, improving digestive functions, and most of the other benefits probiotic supplements can provide. CFU numbers on probiotic supplements can vary anywhere from several million to 50 billion, but the researchers concluded that effective probiotic dosage for general gut health seems to be in the range of 10 million to one billion CFU/mg per day in humans. Dosage recommendations can vary for specific conditions. For instance, in acute infectious diarrhea treatment, it seems that higher doses of probiotic given for short courses are more effective than lower doses. The study shows that 10 billion CFU of Lactobacillus species during the first 48 hours reduced diarrhea duration by 0.7 days compared to those supplemented with one billion CFU. On the other hand, in patients with acute rotaviral diarrhea, early administration of five billion CFU of L. rhamnosus GG reduced symptoms better than 100 billion CFU after initial treatment, showing that timing of administration may have a great impact on effectiveness. The study also supported the idea that multi-strain probiotics should achieve better results than single-strain probiotics. The therapeutic effects of probiotics are due to a number of mechanisms, such as competition with pathogens, production of bactericidal substances, regulation of immune responses, and intestinal epithelial homeostasis. Different probiotic strains excel at different mechanisms, so diversified collection of strains is ideal for overall health.

How does this information come into play when shopping for probiotics?

We can draw a few conclusions from this information. First, there is a minimum amount of daily probiotics that is necessary to achieve most of the desired probiotic benefits, but that amount is much lower than most probiotic companies suggest. Second, the probiotic variants with tens of billions of CFU per serving are providing far more than is necessary for general gut health. This could mean they are better suited for those suffering from chronic digestive conditions, but it could also mean that higher CFU counts are necessary to compensate for poorer survival rates. It’s impossible to say without seeing survival research for a specific brand. Unfortunately, it seems few companies have performed research on survival rates, so only a few companies have this information publicly available. Finally, the rotaviral diarrhea example demonstrates that more is not always better. CFU counts matter, but only to a point. Elements like timing, survival rates, preexisting conditions, diversity of strains, and individual microbiota composition can all have an impact on the needs of an individual and the effectiveness of a probiotic. It’s important to consider all of these factors when searching for a probiotic supplement.

1Bertazzoni, E., Donelli, G., Midtvedt, T., Nicoli, J., & Sanz, Y. (2013). Probiotics and clinical effects: is the number what counts?. Journal of chemotherapy (Florence, Italy), 25(4), 193–212.

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