How to Choose a Probiotic
There are so many options. Here is what actually separates a good probiotic from an expensive one — and what the number on the front of the box does and doesn't tell you.
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Stand in the supplement aisle for two minutes, and you will be offered fifty billion of something, then a hundred billion of something else, in a shinier box. It is a strange way to shop. Nobody buys bread by cell count.
So here are the things that are worth looking at, roughly in the order a scientist would look at them — and, at the end, an honest account of where Flourish sits against each one.
First: what actually counts as a probiotic?
The word gets used loosely enough that it is worth pinning down. The International Scientific Association for Probiotics and Prebiotics (ISAPP) defines probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host."1
Twelve words, and three of them are doing real work: live, adequate amounts, and health benefit. A product that misses any one of those is not a probiotic in the sense the science means. It might still be a perfectly nice powder. It just isn't that.
Beneficial bacteria have been quietly propping up human diets for as long as there have been human diets, which is a story for another day — we tell it in PRO-101.
The keys to a good probiotic
1. It has to be alive
The first word in the definition, and the easiest one to lose in manufacturing
Living bacteria do things. They break down the fibres your own digestive enzymes can't touch, and in the process they produce short-chain fatty acids — acetate, propionate, butyrate — that feed your colon cells and act as signalling molecules well beyond the gut.3 Some also synthesise B vitamins for you, essentially as a by-product of getting on with their day.4
One nuance worth having, because you will see it claimed loosely: gut bacteria do not make minerals. Minerals are elements. What fermentation does is lower the pH in the gut, which makes minerals like calcium and magnesium more soluble and therefore easier to absorb.5 A smaller claim, but a true one.
2. A big CFU number is not a quality score
CFU = colony forming units, the standard measure for commercial probiotics
This is the one the industry leans on hardest, and it is the one worth being most sceptical about. ISAPP lists "more CFU is better" as a myth outright,6 and the NIH's own fact sheet says plainly that higher-CFU products are not necessarily more effective than lower-CFU ones.7
That does not mean dose is irrelevant — it clearly matters for some strains and some outcomes. A review of human dose-response studies found a convincing dose effect for antibiotic-associated diarrhoea, and none at all for several other endpoints.8 The useful question isn't "how many?" but "how many of this organism did the human trials actually use?" For orientation, ISAPP's own checklist puts the effective range for most tested products somewhere between 100 million and 50 billion CFU per dose.9
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The number on the front tells you what was put in. It doesn't tell you what it does.
3. It has to survive the trip
An organism that arrives inactive is a very expensive way to eat nothing
Everything a probiotic might do for you depends on it still being alive when it gets where it's going. Gram-positive bacteria have real machinery for coping with acid — proton pumps, membrane changes, repair systems, and a pre-adaptation response that makes an organism already used to low pH better at handling more of it.12 Survival also improves markedly when there is something for them to metabolise on the way through: one study found glucose improved survival of a probiotic Lactobacillus in acid by up to six orders of magnitude.13
Where they do their work is a more open question than you might expect. The colon gets most of the attention, largely because it is what stool samples measure — but nutrient uptake happens in the small intestine, which has denser immune cell populations and closer contact between microbe and host than the colon does.10 Ingested probiotics also make up a far larger share of the population there.11 The honest version: it depends on the strain and on what you're asking it to do.
4. Multiple strains — with a caveat we'd rather say out loud
More names on the label is not the same as more benefit
Your gut runs on a large, mixed community, and a single isolated organism is a different proposition from a group that has grown up together. There's evidence on that side: one review found the mixture beat the single strain in twelve of sixteen head-to-head comparisons — though the authors noted they couldn't rule out that the mixtures were simply delivering a higher total dose.15
And there's evidence on the other side. A systematic review of 65 randomised trials concluded that in most cases single strains performed equivalently to mixtures.14 ISAPP's summary is the one we'd stand behind: having lots of strains is not by itself a guarantee of a better product.6
So we make a multi-strain product because we think a community is the more sensible thing to put in a bottle — not because eleven is a bigger number than one.
5. And the least glamorous one: read the label
Specificity is the tell — vague labels are vague for a reason
ISAPP's guidance for choosing a probiotic is refreshingly unromantic. Look for a product with evidence behind it for the benefit you actually want, since different strains do different things. Look for a label that names the genus, the species, and the strain, and states the potency through to the end of shelf life rather than at the moment of manufacture. Then give it about a month before deciding.2
A company that is confident about what's in its bottle tends to be specific on the label. That is a surprisingly reliable signal.
One thing a probiotic won't do
It's tempting to assume that swallowing a lot of different strains makes your own gut community more diverse. The research doesn't support that. A systematic review of randomised trials in healthy adults found no meaningful change in the diversity or composition of the resident microbiota after probiotic supplementation,16 and a later meta-analysis pooling 22 studies reached the same conclusion across every diversity measure it looked at.17
Probiotics mostly behave as transient visitors — they do their work on the way through rather than by moving in. Which is a decent argument for taking them regularly rather than heroically, and the reason consistency is key.
You'll also see the word dysbiosis used as though it were a diagnosis. It broadly means an imbalance in the gut community associated with disease, but there's no agreed threshold for it and no single reference microbiome to be imbalanced against — a point microbiologists have made pointedly in print.18 Treat it as a useful shorthand, not a test result.
So how does Flourish stack up?
Against the list above, here's the fair account.
Alive: yes, and that's the whole design. Flourish is delivered in the liquid it was fermented in, never freeze-dried and encapsulated.
Named on the label: eleven strains across five genera — Lactobacillus, Bifidobacterium, Enterococcus, Bacillus and Saccharomyces — listed by species, in both Flourish Original and Flourish Junior. They're set out in the chart above and in Get to Know Your Probiotics.
Fermented together: the strains grow as one culture rather than being blended at the end, and in doing so they build their own acidic environment — a finished batch sits at roughly pH 2 to 3. The bacteria in the bottle have therefore spent their entire lives in acid, which is the mechanism we find most persuasive about a living liquid. We'd stop short of promising you a delivery rate; nobody honestly has that number for their product. The Art of the Brew covers how it's made.
What else is in there: because nothing is dried out and reconstituted, the bottle also carries what the culture produced while it grew — metabolites, short-chain fatty acids, enzymes, and amino acids among them. More on that in Flourish Probiotics and Postbiotics and on What's Inside.
And if a capsule suits your life better, that's a legitimate choice — we set out the trade-offs both ways in Why Liquid Probiotics?
Still not sure?
Choosing well is mostly a matter of asking better questions than the packaging invites. If you'd rather talk it through with a person, our Entegro Health Team does exactly that — and for anything to do with a diagnosed condition, medication, or a child, your doctor or a registered dietitian is the right first call, not us.
Flourish is a dietary supplement made to support digestive and microbiome health. It isn't a treatment for any condition. Follow the dosage on the label. Check with your doctor before starting a new supplement, and with your pediatrician before giving one to a child.
Ready to try a living probiotic?
Eleven living strains. One daily shot. For the whole family.
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A few questions we hear a lot
Is a higher CFU count better?
Not by itself. Both ISAPP and the NIH say higher-CFU products are not necessarily more effective.6,7 Dose does matter for some strains and some outcomes,8 so the question worth asking is what dose was used in human studies of that particular organism.
Is a multi-strain product better than a single strain?
The evidence is split, and anyone telling you otherwise is selling something. One review favoured mixtures in twelve of sixteen comparisons;15 a larger systematic review of 65 trials found single strains generally equivalent.14 What matters is whether that specific formulation has been tested for the benefit you're after.
Will taking a probiotic make my microbiome more diverse?
In healthy adults, the trials say no — supplementation doesn't significantly shift the diversity of the resident community.16,17 Probiotics act largely in transit. That's not a mark against them; it's just a different mechanism from the one the marketing usually implies.
Do probiotics have to reach the colon to work?
Not necessarily. The small intestine is a major and long-overlooked site of action, with closer host-microbe contact than the colon and a much higher relative abundance of ingested organisms.10,11 Where a given strain does its work depends on the strain and the mechanism.
What should I actually look for on the label?
Genus, species and strain; the potency guaranteed through the end of shelf life rather than at manufacture; and evidence for the benefit you want.2 Then give it around a month.
Do gut bacteria really make vitamins?
Vitamins, yes — B-group vitamins in particular are synthesised by gut bacteria.4 Minerals, no; those are elements. What fermentation does is lower gut pH, which improves how well minerals dissolve and absorb.5
Is dysbiosis a diagnosis?
No. It's a broad term for a gut community imbalance associated with disease, but there's no agreed quantitative definition and no single healthy reference microbiome.18 Useful shorthand, not a test result.
About this article
Written by: Lorilyn Van Dyke, Entegro Health | Originally published: November 2021
Important information
This article is for general education and isn't a substitute for professional medical advice, diagnosis, or treatment. Probiotic effects are specific to the strain and to the outcome being studied; evidence for one product does not transfer to another. Follow the dosage printed on the product label. Always speak to your physician or a registered dietitian before starting a new supplement, particularly if you are immunocompromised, seriously ill, pregnant, or giving a supplement to a child. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
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- Hill, C., Guarner, F., Reid, G., et al. (2014). Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology, 11(8), 506–514. Source
- International Scientific Association for Probiotics and Prebiotics. How to choose a probiotic. Source
- Koh, A., De Vadder, F., Kovatcheva-Datchary, P., & Bäckhed, F. (2016). From dietary fiber to host physiology: short-chain fatty acids as key bacterial metabolites. Cell, 165(6), 1332–1345. Source
- LeBlanc, J. G., Milani, C., de Giori, G. S., et al. (2013). Bacteria as vitamin suppliers to their host: a gut microbiota perspective. Current Opinion in Biotechnology, 24(2), 160–168. Source
- Bermúdez-Humarán, L. G., Chassaing, B., & Langella, P. (2024). Exploring the interaction and impact of probiotic and commensal bacteria on vitamins, minerals and short chain fatty acids metabolism. Microbial Cell Factories, 23(1), 172. Source
- International Scientific Association for Probiotics and Prebiotics. Probiotics: Dispelling Myths — "a greater number of colony forming units (CFU) does not always equate with enhanced effects." Source
- National Institutes of Health, Office of Dietary Supplements. Probiotics — Health Professional Fact Sheet. Source
- Ouwehand, A. C. (2017). A review of dose-responses of probiotics in human studies. Beneficial Microbes, 8(2), 143–151. Source
- International Scientific Association for Probiotics and Prebiotics. Making a Smart Selection: Probiotic Checklist. Source
- Jensen, B. A. H., Heyndrickx, M., Jonkers, D., et al. (2023). Small intestine vs. colon ecology and physiology: why it matters in probiotic administration. Cell Reports Medicine, 4(9), 101190. Source
- Judkins, T. C., Archer, D. L., Kramer, D. C., & Solch, R. J. (2020). Probiotics, nutrition, and the small intestine. Current Gastroenterology Reports, 22(1), 2. Source
- Cotter, P. D., & Hill, C. (2003). Surviving the acid test: responses of Gram-positive bacteria to low pH. Microbiology and Molecular Biology Reviews, 67(3), 429–453. Source
- Corcoran, B. M., Stanton, C., Fitzgerald, G. F., & Ross, R. P. (2005). Survival of probiotic lactobacilli in acidic environments is enhanced in the presence of metabolizable sugars. Applied and Environmental Microbiology, 71(6), 3060–3067. Source
- McFarland, L. V. (2021). Efficacy of single-strain probiotics versus multi-strain mixtures: systematic review of strain and disease specificity. Digestive Diseases and Sciences, 66(3), 694–704. Source
- Chapman, C. M. C., Gibson, G. R., & Rowland, I. (2011). Health benefits of probiotics: are mixtures more effective than single strains? European Journal of Nutrition, 50(1), 1–17. Source
- Kristensen, N. B., Bryrup, T., Allin, K. H., et al. (2016). Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Medicine, 8, 52. Source
- Éliás, A. J., Földvári-Nagy, K. C., Al-Gharati, Y. Z., et al. (2026). Effect of probiotic supplementation on the gut microbiota diversity in healthy populations: a systematic review and meta-analysis of randomised controlled trials. BMC Medicine, 24, 71. Source
- Brüssow, H. (2020). Problems with the concept of gut microbiota dysbiosis. Microbial Biotechnology, 13(2), 423–434. Source
