CFU count: does a bigger number mean a better probiotic?
Every probiotic shouts a CFU number: 10 billion, 50 billion, 100 billion. Bigger must be better, right? Not really. Here is what CFU actually measures, and why strain and survival matter far more than the size of the number.
Grounded in 3 peer-reviewed studiesThe quick version
Key takeaways
01What CFU actually means
CFU stands for colony-forming units. It estimates how many live bacteria in a dose are capable of dividing and forming a colony. It is a measure of how many, at the moment of manufacture or through the expiry date.
What it does not tell you: which strains those bacteria are, whether they will survive your stomach, or whether they do anything useful once they arrive.
No
is a bigger CFU always better?
dose-response is not linear
Strain
matters more than the count
benefits are strain-specific
Alive
the count only counts if they arrive
survival beats headline numbers
CFU measures quantity of live bacteria, not whether they are the right ones or will survive.
02Is a bigger number better?
Not on its own. The relationship between dose and benefit is not a simple straight line; for many outcomes there is a range that works, beyond which more CFU does not add more benefit. 1 A 100-billion count of a strain that does nothing for your goal is not better than a well-chosen 10-billion.
03Strain matters more than count
Probiotic benefits are strain-specific: a benefit shown for one strain does not transfer to another, even a close relative. 2 This is why a serious label names its exact strains, not just a genus. The strain tells you what it might do; the CFU only tells you how much of it is there.
04And survival matters most
Even the right strain at the right dose is useless if it does not arrive alive, and whether it establishes at all varies from person to person. 3 That is why we care more about strains chosen to survive the trip than about a big number that never makes it downstream.
The bottom line
Don't buy the biggest number on the shelf. Buy named strains, chosen to survive, at a sensible dose. CFU is how much, not how good.
From this article
The Shield
20 billion CFU of strains chosen to survive the trip.
Shop →Frequently asked questions
What does CFU mean on a probiotic?
CFU means colony-forming units: an estimate of how many live bacteria in a dose can divide and form colonies. It measures quantity of live organisms, not which strains they are or whether they survive.
Is a higher CFU probiotic better?
Not necessarily. Dose-response is not linear and benefits are strain-specific, so more CFU of the wrong strain adds nothing. The right strains that survive matter more than a bigger number.
How many CFU should a probiotic have?
Enough to match the strains and the research behind them, which is often in the billions but not always the highest number available. Look for named strains at a dose backed by studies rather than the biggest headline figure.
Why do probiotic CFU numbers vary so much?
Because CFU is easy to print big and different strains work at different doses. A high number can be marketing; the strain list and survival are what tell you if a product is well designed.
Peer-reviewed & published in
Probiotic dose-response is endpoint-specific; higher CFU is not universally better
Ouwehand AC
Read the 2017 studyProbiotic benefits are strain-specific (expert consensus)
Hill C et al.
Read the 2014 studyProbiotic gut colonization is person-specific, not guaranteed by dose
Zmora N et al.
Read the 2018 studySources are peer-reviewed research on the topics discussed, not studies of finished Stillbelly products. These statements have not been evaluated by the FDA.
Educational content, not medical advice. These statements have not been evaluated by the FDA. Talk to your healthcare provider about persistent digestive symptoms.
