Probiotic Supplements: Strains, CFU and How to Read the Label

Probiotic labels use a vocabulary that appears nowhere else on the supplement shelf. Understanding three things — strain names, CFU counts and when that count is guaranteed — is most of what separates an informed purchase from a guess.

Strains, not species

A full strain designation has three parts: genus, species and strain, as in Lactobacillus rhamnosus GG. Research is conducted on specific strains, and findings do not transfer automatically between strains of the same species. A label naming only a genus and species is telling you less than it appears to. See probiotic strains explained.

What CFU means

Colony forming units count viable organisms, usually stated in billions. A higher number is not automatically better — it is one variable alongside which strains are present and whether they survive to where they are meant to act. Our CFU guide covers how to read the figure.

The detail most labels bury

CFU counts decline over shelf life. A product stating its count at manufacture is making a weaker commitment than one stating the count at expiry, and the difference between the two can be substantial. Storage requirements matter for the same reason — some products need refrigeration and say so in small print.

Prebiotics, probiotics and synbiotics

Prebiotics are fibres that feed bacteria; probiotics are the organisms themselves; products combining both are sold as synbiotics. They are not interchangeable and are dosed in different units — grams for the first, CFU for the second. See prebiotics vs probiotics.

Safety

Probiotics are widely used, but they are live organisms and are not appropriate for everyone. People who are severely immunocompromised, critically ill, or have central venous catheters should not take them without medical supervision. If you are taking antibiotics, timing questions come up frequently — see probiotics and antibiotics, and ask your pharmacist.

Comparing products

Our probiotic supplement comparison filters by brand, strength, format and pack size.

References

• NIH Office of Dietary Supplements — Probiotics (Health Professional Fact Sheet)
• NCCIH — Probiotics: What You Need To Know