🧬 Probiotics, Prebiotics, Synbiotics, Postbiotics and Metabiotics: The Complete Classification
Five terms that are easy to mix up — and what actually works and when
The terms "probiotics", "prebiotics", "synbiotics", "postbiotics" and "metabiotics" are used so often that their meaning has become blurred. Many people treat them as synonyms, yet they are fundamentally different things: some are living microorganisms, others are food for them, and still others are the products of their activity.
In this article we will bring order to the terminology, look at what science says about each class, and give practical rules for choosing and taking them. You will learn how a probiotic differs from a prebiotic, why postbiotics matter, and why the term "metabiotic" is actively promoted by manufacturers.
The gut microbiome: why everyone talks about it
The microbiome is the community of trillions of microorganisms (bacteria, fungi, viruses) living in the human body, mainly in the colon. By modern estimates, the gut hosts around 100 trillion microbial cells, and the collective bacterial "metagenome" carries dozens of times more genes than the human genome itself.
Microbiota performs several key functions: it helps digest fiber, synthesizes vitamins (for example, vitamin K and part of the B vitamins), trains the immune system, protects against pathogens and participates in metabolism. Disruption of the microbiota balance — dysbiosis — has been linked to a wide range of conditions, from antibiotic-associated diarrhea to irritable bowel syndrome.
Diversity
The more diverse the microbiome, the more resilient it is. A poor microbiome is associated with worse metabolic markers.
Not "good vs bad"
What matters is not the mere presence of "bad" bacteria, but the ratio and function of the whole ecosystem.
Whole-body effects
The microbiome affects not only the gut but also immunity, mood and metabolism via the gut–brain axis.
Food and supplements
Probiotics, prebiotics and other classes are tools to support this ecosystem, not a replacement for a healthy diet.
Probiotics: living microorganisms
Probiotics are live microorganisms that, when taken in adequate amounts, confer a health benefit on the host. Most often these are lactobacilli (Lactobacillus), bifidobacteria (Bifidobacterium) and the yeast Saccharomyces boulardii.
| Group | Examples | Common use |
|---|---|---|
| Lactobacillus | L. rhamnosus GG, L. casei, L. acidophilus | Gut health, protection against diarrhea |
| Bifidobacterium | B. longum, B. lactis, B. animalis | Gut, constipation, immunity |
| Yeast | Saccharomyces boulardii | Traveler's diarrhea, antibiotic-associated diarrhea |
| Streptococcus | S. thermophilus | In dairy and complex formulas |
Prebiotics: food for beneficial bacteria
Prebiotics are non-digestible food components that selectively stimulate the growth and activity of beneficial bacteria. They are not living organisms but "food" for them. The best-known prebiotics are inulin, fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), resistant starch and fiber.
The main difference from probiotics: prebiotics contain no live bacteria and are not affected by stomach acid, antibiotics or temperature. They reach the colon, where beneficial bacteria ferment them as a substrate, gaining energy and multiplying.
| Prebiotic | Sources | Comment |
|---|---|---|
| Inulin | Jerusalem artichoke, chicory root, onion, garlic | One of the most studied prebiotics |
| Fructo-oligosaccharides | Bananas, onion, asparagus, supplements | Well fermented by bifidobacteria |
| Galacto-oligosaccharides | Milk, dairy products | Often added to infant formulas |
| Resistant starch | Cooled potatoes, green bananas, legumes | Food for butyrate-producing bacteria |
| Pectin | Apples, citrus, carrots | Soluble fiber, fermented in the colon |
Synbiotics: probiotic + prebiotic
A synbiotic is a product or supplement that combines both a probiotic (live bacteria) and a prebiotic (food for them). The idea is to simultaneously introduce beneficial bacteria and feed them, improving their chances of colonizing and multiplying.
Live bacteria + food for them
The prebiotic gives the probiotic bacteria a substrate for growth after intake.
Convenient
Often one product is enough instead of two. Many complex supplements are synbiotics.
Postbiotics and metabiotics: bacterial "products"
Postbiotics are substances produced through the metabolic activity of beneficial bacteria that confer a health benefit. They include short-chain fatty acids (butyrate, propionate, acetate), bacterial enzymes, vitamins, peptides and other metabolites.
| Type | Examples | Benefit |
|---|---|---|
| Fatty acids | Butyrate, propionate, acetate | Energy for gut cells, barrier support |
| Enzymes | Hydrolases, β-galactosidase | Help with digestion |
| Cell components | Peptidoglycans, teichoic acids | Immune modulation |
| Metabolites | Vitamins, amino acids | Metabolic support |
How to choose: strains, doses, forms
The choice of a supplement depends on your goal. There is no "best" probiotic — there are strains with evidence for specific conditions.
| Goal | Strains with evidence | Comment |
|---|---|---|
| Antibiotic-associated diarrhea | L. rhamnosus GG, S. boulardii | Start at the beginning of the antibiotic course |
| IBS, bloating | B. animalis subsp. lactis, L. plantarum | A course of at least 4–8 weeks |
| Constipation | B. lactis, L. casei | Evaluate the effect after a few weeks |
| General support | Lactobacillus + Bifidobacterium complexes | Look at the listed strain and CFU |
Look for: the specific strain (not just the species), the CFU count through the end of the shelf life (not just at manufacture), the dosage form (capsules resistant to stomach acid) and storage conditions.
How to take: schedule, duration, combinations
Rules for taking depend on the product, but there are general recommendations:
Schedule
Many probiotics are taken on an empty stomach or with food. For resistance to stomach acid, choose coated capsules or strains with proven survival.
Duration
Live bacteria generally do not "colonize" forever: after you stop, they gradually disappear. So courses are usually repeated or combined with prebiotics to sustain the effect.
Pairing with antibiotics
If you take a probiotic during antibiotic therapy, separate the doses by at least 2 hours and continue for several weeks after the course.
Food and prebiotics
Fermented foods (yogurt, kefir, sauerkraut) are a natural source of live cultures, while fiber and vegetables are a source of prebiotics.
What is the difference between a probiotic and a prebiotic?
A probiotic contains live microorganisms, while a prebiotic is non-digestible food that stimulates the growth of beneficial bacteria.
What is a synbiotic?
A product or supplement that combines both a probiotic (live bacteria) and a prebiotic (food for them).
What is a postbiotic?
Substances produced through the activity of bacteria — for example, short-chain fatty acids. They provide benefits without live microorganisms.
Are metabiotic and postbiotic the same thing?
The meaning is close: both refer to products of bacterial metabolism. "Metabiotic" is more of a marketing term, "postbiotic" is used in scientific literature.
Which probiotics are the best?
There is no "best" for everyone. It depends on the goal: for antibiotic diarrhea — L. rhamnosus GG and S. boulardii, for constipation — B. lactis, and so on.
What does CFU on the label mean?
Colony Forming Units — the number of viable microorganisms in a dose. For adults, usually 1–10 billion CFU per day.
Can probiotics be taken every day?
Yes, they are considered safe for most people. But live bacteria do not colonize for long, so courses are usually repeated.
Do probiotics help with antibiotics?
Yes, certain strains (LGG, S. boulardii) reduce the risk of antibiotic-associated diarrhea. Take them at least 2 hours apart.
Can prebiotics cause bloating?
Yes, bloating and gas are possible with a sharp increase in dose. Start with small doses and increase gradually.
Do healthy people need probiotics?
Not necessarily with a balanced diet, but fermented foods and fiber are beneficial.