How to Read a Probiotic "Proprietary Blend" Label

Written by: Taylor Cottle, PhD |October 16, 2026

Time to read 10 minutes

How to Read a Probiotic "Proprietary Blend" Label

A magnifying glass examining a generic supplement label

A probiotic proprietary blend label gives the blend's total weight and names its strains from heaviest to lightest by weight. It does not have to show how much of any single strain you get. Strain codes identify exactly which microbes are inside, "at expiration" tells you when the count applies, and a disclosed per-strain amount lets you compare the serving with a research dose.

This matters when two bottles make similar weight or waist claims and you want to know which one matches the research.

What does FDA require on a proprietary blend label?

The rule is 21 CFR 101.36(c). A supplement can group ingredients under the term "Proprietary Blend" or a descriptive or fanciful name, as long as three things appear on the Supplement Facts panel.¹

1. The blend's name, on its own line.
2. The total weight of the blend, to the right of that name. Under the regulation, that number is the total weight of all the "other dietary ingredients" in the blend.¹
3. The name of each of those other dietary ingredients, listed "in descending order of predominance by weight" and indented under the blend name.¹

What the rule leaves out is the amount of each individual ingredient. That's the whole point of the format. Ingredients that have their own declaration rules under paragraph (b)(2), such as vitamins, minerals, calories, and carbohydrates, still follow those rules inside a blend. The blend format covers only the "other dietary ingredients" without an established Daily Value, which is where probiotic strains sit.¹

A separate rule covers the unit of measure. Inside the Supplement Facts box, FDA's regulation quantifies live microbes by weight, in milligrams, not by colony forming units (CFU). FDA says so directly in its guidance on the topic: within the Supplement Facts label, these ingredients "can be quantified only by weight."² A CFU number elsewhere on the package is allowed as long as it isn't false or misleading.²

Why the order on the label is not the same as the live count

Since blend ingredients are listed by weight, it's tempting to read the first strain as "the most bacteria" and the last as "the least." The label doesn't support that reading.

FDA explains why in its own draft guidance. The weight of a microbial ingredient "represents the product's total cellular mass, consisting of both live and dead microorganisms, and therefore does not necessarily correlate with the number of viable microorganisms."² Two strain powders of the same weight can deliver very different live counts.

The trade groups agree with FDA on this point, even where they disagree on the solution. The Council for Responsible Nutrition and the International Probiotics Association recommend listing blend ingredients in descending order by CFU and note that "CFUs do not directly correlate directly with weight."³

So treat the order as a weight ranking. It tells you which strain powder makes up more of the capsule's mass, not which one delivers the dose used in a trial.

Is the CFU count measured at manufacture or at expiration?

In September 2018, FDA published a draft guidance saying it intended to use enforcement discretion when companies add a CFU count to the Supplement Facts panel alongside the required weight.²,⁴ FDA's guidance page still labels this document a draft, so treat it as FDA's stated intent rather than a finalized rule.⁵

Among the draft's conditions: weight comes first, and the CFU figure has to be clearly separate, such as in parentheses or on a subset line. The CFU figure has to be easy to understand, accurate, and not misleading, and it has to count only live organisms. Strains in a proprietary blend still go in descending order by weight, and the rest of the label has to comply with the law.² FDA's reasoning was that CFU on the panel would help shoppers "more easily compare products" and would promote confidence in the number of viable microorganisms "throughout the shelf life of the product."²

Look closely at the timing language printed next to the number. Bacteria die off during storage, so a count measured at the factory can be higher than what's left months later. CRN and IPA's voluntary best practices recommend that the labeled count "reflect the quantity of live microorganisms at the end of the stated shelf life, not at the time of manufacture."³

You'll see both styles on real labels:

Metagenics UltraFlora Control lists a single strain, Bifidobacterium lactis B-420, at 113.1 mg with "10 Billion CFU. At date of expiration," according to its record in the NIH Dietary Supplement Label Database.⁶ That's the weight-plus-CFU format FDA described, with the timing stated.
MenoFit, in its 2022 label record in the same database, lists a 125 mg "MenoFit Proprietary Probiotic Blend" with "25 Billion CFU at the time of manufacture," covering four coded strains, B-420 among them.⁷

If a label gives a CFU number with no timing at all, you can't tell which of these two it means. That's a fair question to send the brand.

Why a strain code like B420 or HN019 tells you more than a species name

A species name such as Bifidobacterium animalis subsp. lactis covers many different strains. B420 and HN019 both belong to that same subspecies, yet they were studied for different things. B420 was tested for body fat in adults with overweight or obesity,⁸ and HN019 was tested for gut transit time.⁹ The species name alone would not tell you which body of research applies.

A 2018 systematic review of 228 trials found evidence that probiotic benefits are both strain-specific and disease-specific, and it warned that pooling different strains together can lead to "misleading conclusions of efficacy." Its three authors disclosed advisory roles with a probiotic company.¹⁰ CRN and IPA likewise recommend that labels identify the genus, species, and strain for every microorganism in a product.³

Physician's Choice THIN 30 lists a 45 mg probiotic blend with 15 billion CFU of total probiotic activity. Five of its six entries carry a strain code, such as L. plantarum (Lp-115) and B. lactis (BL-04), and one is listed as L. gasseri without a code.¹¹ For the five coded entries, you can look up the published work on that exact strain. For the uncoded one, you can only look up the species.

Provitalize lists three coded strains, L. gasseri SBT2055, B. breve IDCC 4401, and B. lactis R101-8, together with fructo-oligosaccharides inside a 400 mg proprietary synbiotic blend, without individual amounts.¹² The codes let you trace each strain to its research, while the blend format keeps the per-strain split off the panel. Seed's DS-01 product page describes a 24-strain formula and gives counts for four functional blends, such as a 224 mg Digestive Health Probiotic Blend at 38.7 billion AFU, rather than for each strain.¹³

How to compare a label against the research dose

Use these checks when you compare a label with a clinical trial.

Step 1: Write down each strain code. No code means you are working at the species level, and the dose check below won't be precise.

Step 2: Find the daily dose used in the trial. Use the trial itself, not a summary on a product page. Two examples:

In the B420 body-fat trial (Stenman 2016), 225 adults aged 18 to 65 with a BMI of 28 to 34.9 were randomized; people with diabetes, cardiovascular disease, or recent use of anti-obesity medication were excluded. The target dose was 10 billion (10¹⁰) CFU a day, taken as a powder mixed into a smoothie for six months. The packaged dose was 1.3 to 1.4 × 10¹⁰ CFU to allow for loss over the study, and returned sachets still held about 1.1 × 10¹⁰ CFU a day.⁸ In the main intention-to-treat analysis (209 of the 225 randomized), body-fat change did not differ significantly between groups. Among people who followed the protocol closely, the overall four-group comparison still wasn't significant; in the pairwise comparisons, B420 plus a fiber reduced body fat compared with placebo, while B420 alone did not reach significance. Body-fat and waist reductions for B420 as a factor came from an analysis added after unblinding that pooled the two B420 groups. DuPont, which owned the B420 business at the time, fully funded the trial, helped interpret the data, and employed the lead author.⁸
In the HN019 dose study (Waller 2011), 100 adults aged 25 to 65 who reported only one to three bowel movements a week were randomized to 1.8 billion CFU, 17.2 billion CFU, or placebo daily for 14 days, and 88 had transit data at both time points. Average transit time fell in both HN019 groups but not with placebo, the change differed across the three groups, and the drop was larger at the higher dose. Fonterra Research Centre, which supplied the strain, provided financial support.⁹

Step 3: Match the units. CFU comes from growing bacteria on plates and counting colonies. AFU, which some brands use, comes from flow cytometry, and there is no universal one-to-one conversion between the two; the relationship varies by organism, product, and storage. If the trial reports CFU and the label reports AFU, the numbers can't be lined up directly.

Step 4: Check the timing language. A count "at expiration" is a minimum the brand stands behind for the life of the bottle. A count "at manufacture" describes the bottle on day one. Trials report dose in different ways, as the B420 trial's target, packaged, and returned-sachet counts show, so match the timing as closely as the paper allows.

Step 5: Decide what kind of product you're comparing. A single-strain capsule makes the number comparison simple, as with UltraFlora Control's 10 billion CFU of B-420 at expiration.⁶ The capsule format, daily routine, and study population can still differ from the trial. A multi-strain label that reports a total count lets you confirm which strains are present, the overall live count, and when that count applies. To match each strain to its trial dose, you need the per-strain numbers, which is where the questions below come in.

Questions to ask a brand when a strain's CFU isn't listed

When a blend doesn't break out the strain you care about, ask. Here are the questions worth sending:

1. "How many CFU of [strain code] does one serving provide, and is that measured at manufacture or at the end of shelf life?"
2. "Is the CFU count for the blend guaranteed through the expiration date printed on the bottle?"
3. "Is the strain in this product the same strain used in the study you cite, from the same supplier?"
4. "How is the count measured: plate count (CFU), flow cytometry (AFU), or another method?"
5. "What storage conditions does the shelf-life guarantee assume? Is refrigeration needed after opening?"
6. "Has the finished product been tested by an outside lab for strain identity and count?"

A specific answer to the first two questions fills in what a total CFU number on the front of the box can't. If you are comparing several products, ask each brand the same questions so the answers line up.

Why we name every strain in WonderBiotics Probiotics for Weight Management

When we designed WonderBiotics Probiotics for Weight Management, we listed every strain with its code so you can trace each strain to its own research. The formula combines 8 named strains, 20 billion CFU in total per serving, with dihydroberberine and a lemon extract standardized to 70% eriocitrin.¹⁴ The eight are B. lactis B420, B. lactis HN019, L. acidophilus NCFM, L. rhamnosus GG, L. salivarius Ls-33, Lactococcus lactis Ll-23, L. paracasei Lpc-37, and L. plantarum Lp-116.¹⁴ Every one of those codes can be typed into PubMed.

A strain code lets you search for research on that exact strain, and the amount of evidence varies from strain to strain and outcome to outcome. B420 links to the body-fat work above. HN019 links to transit-time and regularity research, which is a gut-comfort role, not a weight claim. With each strain identified by code, the B420 findings stay with B420 and the HN019 findings stay with HN019.

Our once-daily formula combines strain-specific research with additional metabolic ingredients, rather than treating total CFU as the whole comparison. The serving provides B420 at 10 billion CFU, HN019 at 2 billion, and NCFM at 1 billion, with five other named strains contributing 7 billion CFU together. The blend is formulated to provide at least 20 billion CFU at expiration.¹⁵ Those disclosed amounts make the anchor strains easier to compare with research, while differences in delivery format, other ingredients, and study population still matter. Matching a strain's count does not make the finished capsule clinically equivalent to its trial preparation.

Safety notes before you start any probiotic

Probiotics and the other ingredients discussed here are supplements that support a healthy routine. They don't treat obesity or any disease. None of the trials above enrolled people taking semaglutide or tirzepatide.

During pregnancy or breastfeeding, avoid supplements containing berberine.¹⁶ DHB has not been established as safe in these populations, so avoid DHB-containing products, including our formula, as a precaution as well.¹⁴ This restriction concerns berberine or DHB in a combination formula, rather than probiotics as a whole. If you are immunocompromised or take prescription medication, including GLP-1 drugs or glucose-lowering medicine, consult your doctor before starting a probiotic or combination supplement. Never stop or change a prescribed medication to try a supplement instead.