Probiotic Supplements: Strains, CFUs & How to Choose

Live culture supplements look fairly simple until you start comparing the labels. One pack might state 5 billion live microorganisms per capsule, another 50 billion, and another several hundred billion per sachet. Some list a single organism, others list nine. Storage instructions range from ordinary room temperature to strict refrigeration.

Those differences make the category difficult to judge on the headline number alone. A higher CFU count does not automatically tell you that one product suits you better than another, and a longer strain list does not automatically make a formula more appropriate.

This guide explains how to compare probiotic supplements by looking at the details that genuinely differ between products: which microorganisms are listed, how precisely they are identified, CFU per serving, formula, format and storage requirements.

What are probiotic supplements?

The NHS describes probiotics as live bacteria and yeasts that are usually added to yoghurts or taken as food supplements. In retail terms, they are sold in formats including capsules, powders and sachets.

The important point when shopping the category is that "probiotic" does not describe a single ingredient. Different products contain completely different organisms, strains, quantities and combinations.

Two products sitting side by side in the same category should not be treated as interchangeable simply because both contain live cultures. The organism list is where the real differences begin.

Understanding the names: genus, species and strain

One of the biggest differences between live culture products is how precisely the microorganisms are identified.

A real example from our own range shows why this matters. Two OptiBac products both contain the species Lactobacillus acidophilus — but they identify different strains of it:

• OptiBac For Every Day lists L. acidophilus Rosell-52
• OptiBac For Every Day Max Strength lists L. acidophilus NCFM

Same genus. Same species. Different strain designation, and different formulations built around them. If you compared these two products only by the words "Lactobacillus acidophilus", you would miss that distinction entirely.

Not every label provides strain-level identification, so where a manufacturer does supply it, that is a useful detail to note when comparing formulas.

Common microorganisms you may see on labels

The names can look complicated at first, particularly because bacterial taxonomy has been revised over time and several organisms now appear under updated genus names.

Across live culture supplements, you may encounter:

• Lactobacillus and related genera — a broad group frequently seen on labels. Reclassification means you may also see updated names such as Lacticaseibacillus and Lactiplantibacillus; Vivomixx Neo uses both of these alongside Lactobacillus acidophilus.
• Bifidobacterium — another genus commonly represented in multi-strain formulas. Examples in our range include Bifidobacterium breve, Bifidobacterium animalis subsp. lactis and Bifidobacterium lactis.
• Lactococcus — some multi-strain products include organisms such as Lactococcus lactis, sometimes with a specific strain designation.
• Streptococcus thermophilus — another organism that appears in some multi-strain live culture formulations.
• Saccharomyces — unlike the organisms above, this is a yeast rather than a bacterium. Products built around it, such as OptiBac Saccharomyces Boulardii, are a structurally different type of formula.

The practical lesson is straightforward: look past the category name and read the organism list.

What does CFU mean?

CFU stands for colony-forming units. It is the standard way of expressing the quantity of viable microorganisms in a live culture product — each unit representing a cell capable of forming a colony.

You will usually see the figure expressed in billions: 5 billion, 20 billion, 50 billion, or substantially higher.

The number is useful, but only once you know what it actually refers to.

CFU per capsule versus CFU per serving

A product supplying its stated CFU in a single capsule is structured differently from one reaching the same total across two or three capsules, or across a powder serving. When you are comparing packs, check:

• the CFU per capsule or per sachet
• the recommended serving
• how many servings the pack contains

When is the CFU count guaranteed?

This is a genuinely useful label detail and not every product states it.

Some manufacturers declare that the stated quantity of live microorganisms is guaranteed until the end of the product's expiry date. That is a more precise statement than a figure describing only the amount present at the point of manufacture. Both OptiBac For Every Day and For Every Day Max Strength state that their counts are guaranteed until the end of expiry.

Where that information is provided, the headline CFU figure becomes considerably more meaningful.

Is a higher CFU count better?

Not automatically.

CFU describes quantity. On its own, it tells you nothing about which organisms are present, how they are identified, or how the product is meant to be taken.

Consider these alongside the number:

• Which microorganisms and strains are listed?
• How many organisms are included?
• Is the CFU stated per capsule or per full serving?
• Is the quantity guaranteed through expiry?
• How must the product be stored?
• What format is it supplied in?
• What does the manufacturer instruct you to take?

A 460-billion sachet and a 5-billion capsule are clearly very different products. The fact that one number is ninety times larger does not mean the two should be compared on that number alone — they are built differently, taken differently and stored differently.

Single-organism versus multi-strain formulas

Single-organism formulas

Some products centre on one organism. OptiBac Saccharomyces Boulardii is a clear example, built around a single yeast and supplying 5 billion live cells per capsule. Fewer ingredients can make the label easier to compare.

Multi-strain formulas

Others combine several organisms in one serving. OptiBac For Every Day lists six strains, while Vivomixx Neo lists nine across several genera.

A longer strain list does not automatically make a formula superior. It means the product has been constructed differently. When comparing multi-strain options, read the organism list alongside the total CFU, serving size and storage requirements.

How to compare probiotic supplements

Rather than starting with whichever pack shows the biggest number, work through a short checklist.

• Exact microorganism and strain — check how specifically each organism is identified.
• CFU per serving — make sure you are comparing equivalent servings, not capsule against sachet.
• CFU guarantee — where stated, check whether the count holds through expiry.
• Number of organisms — single-organism and multi-strain formulas are different design choices.
• Serving size — one capsule, several capsules or a full sachet changes the comparison.
• Format — capsules, powders and sachets suit different routines.
• Storage — some products require refrigeration; others specifically state they do not.
• Additional ingredients — some formulas include fibres such as fructooligosaccharides (FOS).
• Dietary suitability — check vegan, vegetarian and allergen information where relevant.
• Number of servings — compare how long a pack lasts using the recommended directions.

Real examples from our range

Four real products show why this category cannot sensibly be compared on CFU count alone.

Laid out together, the point becomes clear: 5 billion, 50 billion and 460 billion are not three strengths of the same product. They differ in organism profile, number of strains, format, additional ingredients and storage requirements as well as CFU count.

Capsules, powders and sachets

Format matters because it affects how a product fits into your routine.

• Capsules — a fixed, pre-measured serving that is straightforward to carry and take.
• Sachets — a pre-measured powder serving, mixed or taken according to the manufacturer's directions.
• Powders — an option for people who would rather not swallow capsules, though the serving instructions need closer attention.

Do not assume that changing format changes only convenience. The organism profile, CFU quantity, storage requirements and serving size may all change as well.

Storage and shelf life: does a live culture supplement need refrigeration?

Some do and some don't — which is why the pack instructions matter more here than in most supplement categories.

Two real examples from our range sit at opposite ends:

• OptiBac For Every Day states that it does not require refrigeration, which the manufacturer attributes to freeze-drying techniques and the robustness of the strains used.
• Vivomixx Neo states that it should normally be stored refrigerated at 2–8°C, while noting that unopened sachets can be kept at up to 25°C for up to seven days.

Heat, light and moisture can all matter for products containing live microorganisms, but the correct conditions depend on the individual formulation and packaging. Always follow the storage instructions supplied with the specific product rather than applying one rule across the category.

Probiotics and prebiotics: what's the difference?

The terms sound similar but refer to different things.

• Live culture products contain live microorganisms.
• Prebiotic ingredients are different — commonly certain fibres or carbohydrates, which are not themselves live organisms.

Some supplements contain both. OptiBac For Every Day is an example, combining six live culture strains with fructooligosaccharides (FOS) fibres in the same capsule.

When comparing products, treat the live microorganisms and any additional fibre ingredients as separate parts of the formulation rather than assuming the two terms describe the same thing.

Supplements versus fermented foods

Live culture supplements and fermented foods are not automatically interchangeable.

Some yoghurts and fermented foods do contain live microorganisms, but products vary considerably in:

• the organisms they contain
• whether individual strains are identified at all
• the quantity of live microorganisms present
• how that quantity is measured, declared or guaranteed
• serving size and storage conditions

For that reason it is more useful to assess a supplement on its own label and specification than to assume that everything described in live-culture terms provides the same thing.

Safety and suitability

The NHS notes that for most people with a healthy immune system, probiotics appear to be safe and are unlikely to cause unpleasant side effects. It also points out that they are classed as food rather than medicine, and that there is little evidence to support many of the health claims made about them.

Food supplements are not medicines and should not be used to diagnose, treat, prevent or cure disease.

The practical takeaway

The easiest mistake in this category is choosing the product with the largest CFU number or the longest strain list and looking no further.

A more useful comparison asks:

• Which microorganisms and strains are actually listed?
• How many CFUs does the recommended serving provide?
• Is that quantity guaranteed through expiry?
• Is the formula single-organism or multi-strain?
• Are additional ingredients such as FOS included?
• Is it a capsule, sachet or powder?
• Does it need refrigeration?
• How many servings does the pack provide?

Compared on those terms, a 5-billion capsule, a 50-billion capsule and a 460-billion sachet stop looking like three competing numbers and start looking like what they are: genuinely different formulations, suited to different routines.

Sources & further reading

• NHS — Probiotics
• GOV.UK — Great Britain Nutrition and Health Claims (NHC) Register
• ASA / CAP — Food: Probiotic claims

Last reviewed: September 2026.