Do probiotics survive the trip to your gut?

What a CFU number counts

CFU stands for colony-forming units: how many organisms in a dose are still alive and able to reproduce. Live cultures decline over time, faster when warm and faster still when damp.

So the same 50 billion can mean two different products. “50 billion CFU at time of manufacture” describes the batch when it left the factory. “50 billion CFU through the best-by date” is a commitment about the bottle you are holding.

Stomach acid, and what the label can claim about it

Most organisms in a capsule do not make it through gastric acid and bile, which is why formulations lean on delayed-release capsules, acid-resistant strains, or simply a larger starting count. All three are legitimate; none of them means the survival figure is measurable from the label.

Be careful with numbers that sound like measurements of your gut. A product can honestly state what is in the capsule, and can honestly cite a trial on a specific strain. Nothing on a package can tell you how many organisms took up residence in a particular person.

Strain, in full

Genus, species and strain designation: Lacticaseibacillus rhamnosus GG, not “lactobacillus blend”.

Guaranteed through date

Look for the phrase, not just the number.

Storage

Read the panel: some products need a fridge after opening, others are formulated not to.

Prebiotic content

Inulin or FOS feeds cultures and also, in some people, produces gas. Worth knowing before you buy 90 days of it.

The food route

Kimchi, yoghurt with live cultures, fermented vegetables and the more traditional Thai ferments do the same thing without a CFU claim, and they arrive with the rest of the meal. A capsule is a convenience and a way to target a specific studied strain, not a replacement for food.