When choosing a probiotic, it is easy to focus on the number of CFUs displayed on the label. However, as we explored in Article 6, a larger number of microorganisms does not automatically mean a better probiotic. Another important factor is the identity of the microorganism itself—particularly the probiotic strain.

Understanding strains can help consumers look beyond marketing claims and better understand the science behind different probiotic products.

What Is a Probiotic Strain?

Microorganisms are scientifically classified at different levels. You may see a probiotic identified by its genus, species, and then a more specific strain designation.

A strain can be thought of as a particular genetic variant within a microbial species. Microorganisms belonging to the same species can have different characteristics at the strain level.

This distinction matters because two probiotic strains that appear closely related are not necessarily identical in how they behave or interact with the human body.

Scientific guidance on probiotic labelling therefore recommends identifying microorganisms by genus, species and strain designation, rather than simply using broad descriptions such as “friendly bacteria.”

Why Does the Specific Strain Matter?

The scientific definition of probiotics requires live microorganisms to provide a demonstrated health benefit when administered in adequate amounts.

Importantly, research indicates that probiotic effects can differ between strains. A systematic review examining probiotic efficacy found strong evidence that outcomes can be both strain-specific and condition-specific.

This means research conducted using one particular strain should not automatically be used to claim that every strain from the same species—or every probiotic product—will produce the same result.

For example, if researchers conduct a clinical trial using Strain A and observe a particular benefit, it would not automatically prove that Strain B provides that benefit simply because both belong to the same bacterial species.

Strain Matters—but It Is Not the Whole Story

There is an important scientific nuance.

Not every probiotic effect is necessarily unique to one individual strain. Expert consensus recognises that some benefits may potentially be supported at a broader species or group level, depending on the particular effect and available evidence.

Therefore, the most accurate question is not simply:

“Is this a good strain?”

Instead, consumers should ask:

“What evidence supports this particular microorganism or formulation for its intended benefit?”

That distinction is important because probiotic science depends on the specific evidence, not simply the name printed on the label.

What Should You Look for on a Probiotic Label?

A well-described probiotic product should provide useful information about what it contains.

Important details may include the genus, species and strain designation, the number of viable microorganisms—often expressed as Colony-Forming Units (CFUs)—storage instructions and the quantity expected to remain viable through the stated shelf life.

Scientific guidance recommends that probiotic labels identify each strain and state minimum viable numbers at the end of shelf life.

A very high CFU count combined with vague bacterial identification should therefore not automatically be considered superior to a clearly identified, appropriately studied probiotic.

Why Clinical Evidence Matters

Ultimately, the potent evidence for a probiotic comes from appropriately designed research using the specific strain or formulation being evaluated.

Clinical reviews repeatedly caution that results from one probiotic cannot simply be extrapolated to another because different species, strains and combinations can differ in their effects.

This is particularly important when reading claims online. Statements such as “probiotics have been supported by clinical research to…” may be misleading if the research actually involved only certain strains, doses or formulations.

The correct questions are: Which strain was studied? At what dose? For which population? For what outcome?

The Bigger Picture

Choosing a probiotic involves more than finding the biggest number on the packaging.

Strain identity, CFU count, dose, viability, stability, formulation and clinical evidence all contribute to understanding a probiotic product.

The key message is simple: not all probiotics are interchangeable.

Understanding exactly which microorganisms a product contains—and whether credible evidence supports them—is far more informative than relying solely on terms such as “high strength,” “advanced” or “billions of bacteria.”

Get In Touch