Best Probiotic Supplement: How to Choose

What the CFU number actually measures

A probiotic label leads with a colony-forming unit count, or CFU, usually in billions. A CFU is not a cell but a unit of viable growth: the number of colonies a sample forms on a culture plate under stated conditions. Two laboratories can report different figures for the same powder, which is why the number is a guide rather than a guarantee.

The count also says nothing about which organism is inside; a jar can print fifty billion CFU on the front and give only a genus on the back. The two facts that decide whether a label is usable are the strain designations written out in full, and whether the count is guaranteed at end of shelf life or only at time of manufacture.

That distinction is the most useful one on the shelf. At time of manufacture is the count on the day the powder was blended. Guaranteed through end of shelf life states a minimum the maker commits to on the last date printed on the pack. Live organisms decline as they sit, and faster in warmth, so a manufacture-day figure can be a fraction of itself by the expiry date.

The strain designations you will see on a shelf

Effects are strain specific, so a genus and species do not identify the organism. Lactobacillus rhamnosus GG and Lactobacillus rhamnosus GR-1 share a species and differ as strains. A label written out to strain level is the only one worth comparing.

• LGG - Lactobacillus rhamnosus GG, catalogued as ATCC 53103.
• BB-12 - Bifidobacterium animalis subsp. lactis BB-12.
• DSM numbers - culture-collection designations such as DSM 17938; a species name without one is not specific.
• Saccharomyces boulardii - a yeast, not a bacterium, with named strains such as CNCM I-745.
• Multi-strain blends - count the strains named individually; a total CFU behind a proprietary blend gives you nothing to compare.

What we look for, in order

First, strain designations written out to letters or a culture-collection number. Second, the CFU stated as a minimum guaranteed at end of shelf life rather than at manufacture. Third, the delivery format: a delayed-release or enteric capsule is built to pass the stomach rather than open in it. Fourth, whether the jar is single-strain or a named blend, matched to what you set out to buy.

We do not rank on a large CFU number alone, on packaging, or on the words supports and boosts. Cost per billion CFU is the honest comparison.

What a probiotic label is and is not allowed to say

In the United States a dietary supplement may carry a structure or function claim but not a disease claim, and the FDA does not review supplements before they are sold. In the European Union the European Food Safety Authority has authorised no health claim for probiotics, holding that even the word on a food label implies a benefit and needs substantiation. The claim panel is marketing; the Supplement Facts panel and the strain list are the parts held to identity rules.

The picks

Each pick below is justified on properties printed on the product label - form, elemental content, grade, ingredient panel or cost. None is justified by a health claim.