Gut health · Labels
What CFU actually means
(and why the biggest number is not the best)
CFU is a count of living organisms. It says nothing about whether they are the right ones, whether they survive the trip, or whether that number is true on the day you open the bottle.
The definition, without the marketing
CFU stands for colony-forming units: the number of organisms in a dose that can divide and form colonies. It is a viability measure, not a strength measure. 50 billion CFU of a strain that does not survive stomach acid is worth less than 5 billion of one that does.
The three numbers that matter more
| Number | Why it matters |
|---|---|
| Strain name | A genus and species (Lactobacillus rhamnosus) is not a strain. The strain code is what the research was actually done on. |
| Count at expiry | "50 billion at manufacture" can be a fraction of that by the time you finish the bottle. The guarantee should be at expiry. |
| Dose per serving | A big total spread across a large serving is not the same as the same count in one capsule. |
Why survivability is the real question
Stomach acid is designed to kill bacteria. A probiotic has to get past it to matter. Formulation choices — enteric coating, a resistant capsule, a strain selected for acid tolerance, or simply taking it with food — all exist to answer that one problem. A product that ignores it and advertises a large number is advertising the easy half.
A useful question for any brand: what is the count at expiry, and what evidence is there that this strain survives transit? If either answer is vague, the CFU number is decoration.
Do more CFU mean more effect?
Not in a straight line. Research uses specific doses of specific strains, and the effect is tied to that pairing. Doubling a dose of the wrong strain does not double the benefit; it may just double the gas in week one. Multi-strain products are popular because they hedge, but the honest selling point of a multi-strain formula is coverage of different mechanisms, not a bigger total.
What to look for on the label, in order
- Strain codes, listed individually rather than as a genus.
- Count guaranteed at expiry.
- Serving size and how many capsules that is.
- Storage instructions that match how it is shipped.
- Third-party testing statement — an actual lab, not a badge graphic.
This article is general information, not medical advice. Supplements are not a treatment for a diagnosed condition — talk to your doctor or a registered dietitian before starting one, especially if you are pregnant, nursing, taking medication or managing a digestive disease.
Common questions
- Is more CFU better in a probiotic?
- Not necessarily. Effect depends on the strain and the dose used in research. A large count of a strain that does not survive transit is worth less than a smaller count of one that does.
- What is a good CFU count?
- Anywhere from a few billion to tens of billions is common in research-backed products. The count matters less than the strain, the expiry guarantee and whether it survives stomach acid.
- What does CFU at expiry mean?
- That the stated live count is guaranteed until the expiry date, rather than only at manufacture. It is a stronger claim and worth paying attention to.
- Do I need a multi-strain probiotic?
- Not automatically. Multi-strain products hedge across mechanisms; a single well-researched strain can be equally valid if it targets what you actually need.
Read the label properly
Strain names, count at expiry, dose per capsule. That is the whole comparison.
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