Probiotics and prebiotics – what are they, how do they work, and how to use them?

The article was updated on 25.05.2026

Probiotics are live bacteria and yeasts that have a beneficial effect on the body – prebiotics are food substances that nourish them. These are two different tools working towards the same goal: a healthy gut microbiome, which is the ecosystem of trillions of microorganisms inhabiting the human digestive tract. A probiotic provides beneficial microorganisms from outside; a prebiotic feeds those already in the gut. The combination of both in one preparation is a synbiotic.

The difference between them has practical significance: choosing a probiotic without knowing the strain and indication is often a shot in the dark, and most prebiotics can be obtained from the daily diet without any supplementation.

In this article, you will find concrete answers to questions that really matter when choosing: which probiotic strains are best researched and for what, how to read a supplement label, when probiotics are truly needed – and when a change in diet is sufficient.

1. What are probiotics and how do they work?

Probiotics are live microorganisms that – when administered in adequate amounts – confer a health benefit on the host. This is the official definition formulated jointly by WHO and FAO in 2001, which remains valid today in scientific literature and regulations. Two words are key here: live and adequate amounts – not every product containing bacteria deserves the name probiotic.

To understand why probiotics matter at all, we must start with where they act – the human gut microbiome.

1.1. The gut microbiome – what it is and why it matters?

The human digestive tract hosts 10 to 100 trillion microorganisms, representing according to newer metagenomic data up to 1500–2000 species of bacteria, and their total mass is about 0.2-1.5 kg depending on the methodology of the study. This ecosystem – called the gut microbiome – is not a passive passenger. It actively participates in digestion, the production of certain vitamins (including K2, B12, biotin), the regulation of the immune system and – what is increasingly interesting to scientists – the functioning of the nervous system.

The composition of the microbiome is as individual as a fingerprint and develops throughout life. It is influenced by: mode of birth, breastfeeding, diet, medications taken (especially antibiotics), stress, and the environment in which we live. A disturbance of this balance – known as dysbiosis – is associated with a range of health problems: from digestive ailments, through weakened immunity, to inflammatory diseases.

1.2. How do probiotics affect the body?

The mechanisms of probiotic action are complex and largely strain-dependent – the same species of bacteria can act differently depending on the strain. We distinguish several main pathways.

Competition with pathogens

Probiotic strains occupy sites on the intestinal epithelium, making it difficult for pathogenic bacteria to adhere and colonize. This mechanism is called competitive exclusion.

Production of antibacterial metabolites

Probiotics produce organic acids (lactic, acetic), hydrogen peroxide, and bacteriocins – substances that inhibit the growth of undesirable microorganisms and lower the pH of the intestinal environment, making it less hospitable to pathogens.

Strengthening the intestinal barrier

Probiotic bacteria support the tightness of the junctions between intestinal epithelial cells, which reduces the risk of undesirable substances penetrating the bloodstream – a phenomenon commonly known as "leaky gut".

Modulation of the immune system

The intestines contain the largest aggregation of lymphoid tissue in the body – it is estimated that about 70% of human immunocompetent cells are associated with the mucous membrane of the digestive tract. Probiotics communicate with these cells, influencing, among other things, the production of cytokines and lymphocyte activity. Studies indicate that regular intake of appropriate strains can contribute to the proper functioning of the immune system.

Gut-brain axis

This is a relatively new but intensely researched area. The intestines and brain communicate bidirectionally – through the vagus nerve, the hormonal and immune systems. The gut microbiome influences the production of neurotransmitters: about 90% of serotonin in the human body is produced in the intestines by enterochromaffin cells, and the microbiome regulates this process. Similarly with GABA – the main inhibitory neurotransmitter, reducing arousal and anxiety.

Research on so-called psychobiotics – probiotic strains that affect mood and cognitive functions – is still in its initial phase, but the results are promising. A meta-analysis published in General Psychiatry (Yang et al. 2019) suggests that probiotic interventions may contribute to reducing symptoms of depression. The mechanism is not yet fully understood – therefore, claims about probiotics "curing" depression are premature, but the research direction is clear.

Practical conclusion: the state of the gut and the mental state are interconnected. Taking care of the microbiome – through a diet rich in fermented products and prebiotics – is an investment not only in digestion. We also write about how diet affects inflammatory processes related to mood, among other things, in the article Anti-inflammatory diet – what to eat and what to avoid?

1.3. The most important probiotic strains – what you need to know about them?

A probiotic strain is not the same as a species. The full name of a probiotic microorganism consists of three parts: genus, species, and strain code – e.g., Lactobacillus rhamnosus GG. This code is crucial information: two different strains of the same species can have completely different properties and applications. Therefore, when choosing a probiotic, it is always worth checking whether the manufacturer provides the full strain name.

Below is a list of the most commonly used and best-researched strains:

Scroll right to see the full table (on mobile devices) →

1.4. Gut-brain axis – what does the microbiome have to do with mood?

The connection between the gut and the brain – called the gut-brain axis – is one of the most dynamically developing areas of modern science. The gut and brain communicate through multiple channels simultaneously: via the vagus nerve, the hormonal system (e.g., through cortisol and gut hormones), the immune system, and metabolites produced by the microbiome.

The microbiome participates in the synthesis or regulation of several key substances affecting mood and cognitive functions. It is estimated that about 90% of serotonin – a neurotransmitter commonly referred to as the "happiness hormone" – is produced in the gut by enterochromaffin cells, and the microbiome regulates this process. The same applies to GABA – the main inhibitory neurotransmitter, which reduces arousal and anxiety.

Research on so-called psychobiotics – probiotic strains that influence mood and cognitive functions – is still in its preliminary phase, but the results are promising. A meta-analysis published in General Psychiatry (Yang et al. 2019) suggests that probiotic interventions may contribute to reducing symptoms of depression. The mechanism is not yet fully understood – therefore, claims about probiotics "treating" depression are premature, but the direction of research is clear.

Practical conclusion: the state of the gut and the mental state are interconnected. Taking care of the microbiome – through a diet rich in fermented products and prebiotics – is an investment not only in digestion. We also write about how diet affects inflammatory processes related to mood, among other things, in the article Anti-inflammatory diet – what to eat and what to avoid?

2. What are prebiotics and how do they work?

Prebiotics are substances that – unlike probiotics – are not living organisms. They are food components that human digestive enzymes cannot break down in the small intestine. They reach the large intestine undigested, where they become selective nourishment for beneficial gut microbiome bacteria. The word "selective" is key here: a true prebiotic does not feed all bacteria equally, but prefers the beneficial ones – mainly Lactobacillus and Bifidobacterium.

The official definition of a prebiotic, formulated by the International Scientific Association for Probiotics and Prebiotics (ISAPP) in 2017, states: a substrate selectively utilized by host microorganisms conferring a health benefit. Importantly, this definition extends beyond the gut – prebiotics can also act on the microbiome of the skin, respiratory tract, and vagina, although gut prebiotics are by far the best-researched.

2.1. How do prebiotics differ from ordinary fiber?

This question arises frequently, and it is worth clarifying precisely. Every prebiotic is a dietary fiber, but not every fiber is a prebiotic. Fiber is a broad term encompassing all polysaccharides and oligosaccharides undigested by humans. A prebiotic must meet an additional condition: it must selectively stimulate the growth or activity of specific beneficial microorganisms.

For example: cellulose is a dietary fiber – it swells in the intestine, regulates peristalsis, but it is not a selective nutrient for any specific group of bacteria and does not meet the criteria of a prebiotic. Inulin, on the other hand, is both a fiber and a prebiotic – studies consistently confirm its selective effect on the growth of bifidobacteria.

2.2. Types of prebiotics – inulin, FOS, GOS, and others

Not all prebiotics are the same. They differ in chemical structure, origin, site of fermentation in the gut, and the preferred bacteria they stimulate. Below is a discussion of the most important groups.

Inulin and fructooligosaccharides (FOS)

The most extensively researched group of prebiotics. Inulin is a fructose polymer, naturally present in chicory root (up to 48% dry weight), Jerusalem artichokes, and garlic. FOS are short-chain fractions of inulin. Both compounds are a selective nutrient for bifidobacteria and selected strains of Lactobacillus. Inulin is also commonly used as an ingredient in probiotic and prebiotic supplements and as a natural fat and sugar substitute in the food industry.

Galactooligosaccharides (GOS)

Naturally present in breast milk – this is one of the reasons why breast milk so effectively shapes the newborn's microbiome. GOS are industrially produced from lactose and added to infant formula. They primarily stimulate bifidobacteria and are well tolerated even by infants.

Resistant starch

A fraction of starch that resists digestion in the small intestine and reaches the large intestine, where it is fermented by bacteria into short-chain fatty acids (SCFAs) – mainly butyrate, propionate, and acetate. Butyrate is a key energy source for colonocytes (colon cells) and plays an important role in maintaining the integrity of the intestinal barrier.

Resistant starch is present in unripe bananas, cooked and cooled potatoes, and legumes. We have dedicated a separate article to it: Resistant starch – what it is and in which foods it is found?

Pectins

Polysaccharides present mainly in fruit peels – apples, citrus, plums. Fermented by gut bacteria into SCFAs, they exhibit prebiotic properties, although less selective than inulin or FOS.

Beta-glucans

Polysaccharides present in oats and barley. In addition to prebiotic properties, they have a well-documented effect on lowering LDL cholesterol levels – this is one of the few effects for which EFSA has approved a health claim.

2.3. Natural sources of prebiotics in the diet

Prebiotics are commonly available in a plant-based diet – the problem is that the average Western diet provides far too little of them. It is estimated that the recommended daily intake of prebiotics is 5–8g, while the average intake in European countries is about 3–4g per day. Below is a list of the best sources:

Scroll right to see the full table (on mobile devices) →

2.4. How do prebiotics change the microbiome? Research-confirmed effects

Regular consumption of prebiotics leads to measurable changes in the composition of the microbiome – and relatively quickly. DNA sequencing studies show that after just 2–3 weeks of a diet rich in inulin or FOS, the abundance of bifidobacteria and Lactobacillus increases, with a simultaneous decrease in the proportion of potentially pathogenic bacteria from the genera Clostridium and Fusobacterium.

The fermentation of prebiotics by intestinal bacteria leads to the production of short-chain fatty acids (SCFAs): butyrate, propionate, and acetate. Butyrate plays a special role: it is the main energy source for colon cells, exhibits anti-inflammatory properties, and supports the integrity of the intestinal barrier. Propionate goes to the liver and participates in the regulation of glucose levels and cholesterol synthesis. Acetate is absorbed into the bloodstream and serves as an energy substrate for peripheral tissues.

In other words: prebiotics do not act directly on the body – they act through the microbiome, which converts them into metabolites with a wide range of effects. This is what makes a prebiotic-rich diet one of the most effective tools for long-term intestinal health care.

3. Probiotics vs prebiotics – what's the difference and what do they have in common?

Probiotics and prebiotics are two distinct concepts that are often confused or used interchangeably. However, the difference between them is fundamental: a probiotic is a living organism, a prebiotic is a food substance. They share a common goal – both serve the intestinal microbiome – but their mechanisms of action, sources, and principles of use have little in common.

3.1. Probiotic vs prebiotic – comparative table

The following table organizes the key differences in one place:

Scroll right to see the full table (on mobile devices) →

3.2. What are synbiotics?

A synbiotic is a preparation combining a probiotic and a prebiotic in one formula. The idea is simple: if a probiotic needs nutrients to survive and multiply in the gut, then providing these nutrients simultaneously should increase its effectiveness. In practice, however, not every combination deserves this name.

ISAPP distinguishes two types of synbiotics:

• Complementary synbiotic – probiotic and prebiotic selected independently, each with confirmed individual action. The prebiotic does not have to be "tailored" to a specific strain – it acts on the microbiome overall.
• Synergistic synbiotic – prebiotic specifically chosen to be a selective nutrient for the accompanying probiotic strain. This approach requires greater precision and is better documented in clinical trials.

Example of a synergistic synbiotic: Bifidobacterium longum combined with inulin or FOS, which this specific strain ferments exceptionally effectively. Studies on such pairs indicate a stronger bifidogenic effect than when administering only the probiotic or only the prebiotic.

On the supplement market, the vast majority of products described as "synbiotics" are complementary synbiotics – which is not a disadvantage, as long as both components have documented effects. When reading the ingredients, it is worth checking: is the prebiotic named (inulin, FOS, GOS) and in what dose? A vague entry "fiber" without specification is a red flag.

3.3. Postbiotics – what are they and why are they being talked about more and more?

Alongside probiotics, prebiotics, and synbiotics, a fourth term is increasingly appearing: postbiotic. According to the ISAPP definition from 2021, a postbiotic is a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host. In other words: dead bacteria or their fragments which, despite their lack of viability, still exert a measurable effect on the body.

Sounds paradoxical? The mechanism is as follows: bacterial cell walls, their DNA, metabolites (including the same SCFAs that are produced during prebiotic fermentation), and released peptides can interact with immune system receptors and the intestinal epithelium regardless of whether the bacteria are alive. Some studies suggest that postbiotics may be more effective than probiotics in individuals with weakened immunity, where live microorganisms could pose a risk.

Postbiotics also have a practical advantage: they are stable at room temperature, do not require refrigeration, and are resistant to stomach acid. This makes them an interesting alternative or supplement to classical probiotics – especially for the elderly or after intensive immunosuppressive therapies.

3.4. Can probiotics, prebiotics, and postbiotics be used together?

Yes – and in most cases, it makes sense. Probiotics and prebiotics act synergistically: prebiotics provide nourishment for the introduced probiotic strains and for native intestinal bacteria. Postbiotics can complement this pair as a constant element of diet or supplementation, regardless of the state of the intestinal flora.

There is no evidence that simultaneous use of these three forms is harmful in healthy adults. Exceptions are situations described in the chapter on contraindications – primarily severe immune deficiencies, where even standard probiotics require medical consultation.

Practically speaking, the easiest and most effective way to combine all three elements is simply a well-balanced diet: fermented products as a source of probiotics, vegetables and whole grains as a source of prebiotics – and postbiotics will naturally arise as a result of intestinal fermentation. Supplementation is a justified complement when diet is insufficient or when specific, well-documented strains are needed in certain doses.

4. When is it worth reaching for a probiotic? Key indications

Probiotics are not a "cure-all" supplement – their effectiveness is strain-dependent and contextual. However, there are several areas where scientific evidence is solid enough to speak of real benefits, not just potential.

Below is a discussion of the most important indications along with information on which strains have the best research support.

4.1. Antibiotic therapy – when and how to use probiotics?

This is the most common and best-documented indication for probiotic use. Antibiotics do not act selectively – alongside pathogenic bacteria, they eliminate a significant portion of beneficial gut flora. The result is dysbiosis, which can persist for weeks or months after treatment ends, and its most troublesome symptom is antibiotic-associated diarrhea (AAD), affecting 5 to 35% of patients depending on the type of antibiotic used.

Cochrane reviews suggest that probiotics used concurrently with antibiotic therapy can reduce the risk of antibiotic-associated diarrhea, and the best studied strains in this context are Lactobacillus rhamnosus GG and Saccharomyces boulardii CNCM I-745.

A key practical question: when to take probiotics relative to antibiotics? The recommendation is consistent in most guidelines – a minimum of 2 hours between the antibiotic dose and the probiotic. An antibiotic taken simultaneously with a probiotic can eliminate the introduced bacteria before they manage to reach the large intestine. Probiotic therapy should be continued for at least 1-2 weeks after the antibiotic course ends.

4.2. Irritable Bowel Syndrome (IBS) – which strains help?

Irritable bowel syndrome is one of the most common chronic digestive disorders – it is estimated to affect about 10-15% of the population in Western countries. Its symptoms – recurrent abdominal pain, bloating, and irregular bowel movements – are chronic and significantly reduce quality of life. Gut dysbiosis is one of the recognized pathophysiological mechanisms of IBS, making probiotics a logical direction for support.

Research results are heterogeneous – partly because IBS is a heterogeneous disease entity with several subtypes (diarrhea-predominant, constipation-predominant, mixed). Nevertheless, several strains have stronger evidentiary bases:

• Bifidobacterium infantis 35624 – clinical studies have shown a reduction in the severity of abdominal pain and bloating in IBS patients.
• Lactobacillus plantarum 299v – improvement in bloating and pain, especially in the diarrhea-predominant subtype.
• Multi-strain preparations – some meta-analyses indicate the superiority of multi-strain preparations over single-strain ones in IBS, although the evidence is still inconclusive.

Important note: probiotics can alleviate IBS symptoms but do not treat its cause. In some patients, the effect is pronounced, in others minimal – which results, among other things, from the individual baseline microbiome composition. If after 4-6 weeks of regular supplementation there is no improvement, it is worth considering changing the strain or preparation.

4.3. Traveler's Diarrhea

Traveler's diarrhea affects 20% to 60% of people visiting countries with an elevated sanitary risk (mainly South Asia, Sub-Saharan Africa, Latin America). It is most often caused by enterotoxic strains of Escherichia coli, less commonly by other bacteria, viruses, or protozoa.

Prophylactic use of probiotics before and during travel has moderate research support. The best-documented strain for this indication is Saccharomyces boulardii – as a yeast, it is naturally resistant to antibiotics and most unfavorable environmental conditions of the digestive tract. A meta-analysis published in Travel Medicine and Infectious Disease showed that S. boulardii reduces the risk of traveler's diarrhea by about 21% compared to placebo.

It is best to start taking the probiotic 5-7 days before departure and continue throughout the trip. This does not eliminate the risk but can reduce its severity and shorten the duration of diarrheal episodes.

4.4. Immune support – what does research say?

The link between the microbiome and immunity is well-documented. The question of whether probiotic supplementation translates into measurable clinical benefits for immunity is more complex.

Available data indicate that regular use of selected strains can contribute to reducing the frequency and shortening the duration of upper respiratory tract infections. A meta-analysis published in the British Journal of Nutrition (2014), covering 20 randomized clinical trials, showed that probiotics shorten the duration of respiratory tract infections by an average of about 0.77 days. The best-documented strains in this area are Lactobacillus rhamnosus GG, Lactobacillus acidophilus NCFM, and Bifidobacterium longum BB536.

The effect is more pronounced in people with initially weakened immunity: seniors, preschool and school-aged children, and people exposed to chronic stress. In healthy adults with a proper diet, the benefit is smaller, though still measurable.

4.5. Probiotics for women – intimate and vaginal flora

The vaginal microbiome is a distinct ecosystem, physiologically dominated by bacteria of the genus Lactobacillus – primarily L. crispatus, L. iners, and L. jensenii. They maintain an acidic pH (approx. 3.8-4.5), which protects against pathogen proliferation. Disruption of this balance leads to bacterial vaginosis (BV) or candidiasis.

Oral supplementation with probiotic strains that colonize both the intestines and the reproductive tract has increasingly better evidentiary bases. Research indicates the effectiveness of Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 strains – when administered orally, they migrate to the vagina and contribute to the restoration of physiological microflora. The effect is particularly well-documented as an adjunct to antibiotic therapy in recurrent BV.

4.6. Other areas of application – what does research suggest?

Beyond the indications discussed above, probiotics are the subject of intensive research in several other areas. The evidence here is less clear-cut or still preliminary, but worth mentioning.

Skin and atopic dermatitis (AD)

Meta-analyses suggest that probiotic supplementation in pregnant women and infants may reduce the risk of developing AD in high-risk children. The mechanism is linked to modulating the immune response early in life.

Mental health

Research on psychobiotics – as mentioned in chapter 1.4 – is promising but still in its early stages. Preliminary results suggest that selected strains may contribute to reducing anxiety symptoms and improving mood, but large clinical trials with clearly defined endpoints are still lacking.

Metabolism and body weight

Gut dysbiosis is linked to obesity and metabolic disorders. Studies suggest that some probiotic strains may influence lipid metabolism and glucose levels; however, the effects so far are modest and require confirmation in larger studies.

Helicobacter pylori

Several clinical trials have shown that supplementing standard eradication antibiotic therapy with probiotics – particularly Lactobacillus reuteri DSM 17938 and Saccharomyces boulardii – can reduce therapy side effects and slightly increase its effectiveness. Probiotics do not replace antibiotic therapy here, but rather complement it.

5. How to choose a good probiotic? A practical guide to the label

Pharmacy and health food store shelves are now stocked with dozens of probiotic preparations. They differ in price, composition, number of strains, and form of administration – and marketing doesn't make the choice any easier.

Below is a set of specific criteria that will allow you to assess the quality of a preparation without microbiological knowledge.

5.1. Full strain name – why is this the most important information on the packaging?

The first and most important thing to look for on a probiotic label is the full three-part strain name: genus + species + alphanumeric code. For example: Lactobacillus rhamnosus GG, Saccharomyces boulardii CNCM I-745, or Bifidobacterium longum BB536.

Why is this so important? Because probiotic properties are a characteristic of a specific strain, not a species. Lactobacillus rhamnosus without a strain code is a collective term covering hundreds of different strains with different properties – some have confirmed clinical effects, others have not been studied at all. A product with an incomplete name might contain a valuable strain, but you have no way to verify this.

So, on the label, look not only for the species name but also the code. If it's missing – that's a warning sign. Manufacturers who invest in quality and clinical research always provide full strain names, because that is their marketing argument.

5.2. CFU – what does it mean and how much is enough?

CFU (Colony Forming Units) is a measure of the number of living microorganisms capable of multiplying. It is the equivalent of a "dose" for probiotics. On labels, you will find values ranging from hundreds of millions to tens of billions of CFUs per serving.

The common belief that "the more CFUs, the better" is an oversimplification. The optimal dose is strain-dependent and indication-dependent – and results from clinical studies for a specific strain, not from general recommendations. For most applications in clinical practice, effective doses are in the range of 1-10 billion CFUs per day. Preparations with 50 or 100 billion CFUs are not automatically more effective – they may be justified for specific indications, but they are not the standard.

A more important question than "how many CFUs?" is: how many CFUs at the end of the shelf life? The number of live bacteria decreases over time, which is why an honest manufacturer guarantees the declared CFU count until the expiration date, not just on the day of production. Look for the phrase "guaranteed at expiry" or "until expiration date" next to the CFU count on the label.

Scroll right to see the full table (on mobile devices) →

5.3. Does a probiotic need to be stored in the refrigerator?

This is one of the most common questions – and the answer is less obvious than it seems. Traditionally, probiotics required refrigeration because live bacteria lose viability at higher temperatures. However, technological advancements in lyophilization (freeze-drying) and microencapsulation mean that more and more preparations are stable at room temperature.

The key question is not "refrigerator or not?", but "does the manufacturer guarantee the viability of bacteria under the declared storage conditions until the expiration date?" A preparation requiring refrigeration that was at room temperature for an extended period during transport or storage may be significantly less effective than declared on the label. A probiotic stable at room temperature, if its viability in these conditions is confirmed, is more reliable in this regard.

When purchasing online or in stores without a controlled cold chain: choose a preparation stable at room temperature or ensure that the seller stores it correctly. Buying a probiotic requiring refrigeration from a shelf at room temperature is a common mistake that can completely negate the supplement's effectiveness.

5.4. Single-strain or multi-strain probiotic – which to choose?

The market offers preparations containing a single strain (single-strain) and those with several or a dozen strains simultaneously (multi-strain). Which type is better?

The answer depends on the goal:

• Specific clinical indication – choose a single-strain or two-strain probiotic with documented efficacy in that area. If you're looking for support for antibiotic-associated diarrhea, LGG or S. boulardii have repeatedly confirmed efficacy. Adding additional strains without clinical justification does not increase the effect.
• General microbiome and immune support – multi-strain preparations may have an advantage because they act on a wider spectrum of gut functions. Condition: each strain must be listed with its full name and have its own justification in the composition.

Beware of preparations with 10-15 strains where each is listed only by its species name without a code, and the total dose is, for example, 5 billion CFU. For 12 strains, this means an average of about 400 million CFU per strain – a dose too low to show any clinical effect for most of them.

5.5. Form of administration – capsules, sachets, drops, or food?

Probiotics are available in several forms, each with its advantages and limitations.

Enteric-coated capsules

The coating protects bacteria from stomach acid and releases them only in the small or large intestine. This is one of the best forms in terms of survival – strains sensitive to low pH benefit significantly from enteric coating. Look for capsules labeled "DR" (delayed release) or "enteric-coated."

Standard capsules and powders

Effective for strains naturally resistant to stomach acid (e.g., Saccharomyces boulardii, some Lactobacillus strains). Powders to dissolve in water are convenient for children and people who have difficulty swallowing capsules – however, it is important not to mix them with hot liquids, which kill bacteria.

Drops and suspensions

Primarily dedicated to infants and young children. Most often contain Lactobacillus reuteri DSM 17938 or L. rhamnosus GG in oil or aqueous form.

Probiotics in food

Yogurts, kefirs, fermented drinks with added probiotic cultures. Efficacy depends on the number of live bacteria at the time of consumption and their resistance to stomach acid. Fermented dairy products are a valuable dietary supplement but do not replace supplementation for specific clinical indications – primarily because you cannot control the CFU count or specific strains.

5.6. Warning signs – what to avoid when choosing a probiotic?

Finally, a list of warning signs that should raise caution when choosing a preparation:

• Lack of strain codes – only species names without an identifier (e.g., just "Lactobacillus acidophilus" without a code). Impossible to verify in clinical studies.
• CFU listed only "on the day of production" – without a guarantee of viability until the expiration date. The actual bacterial content at the time of consumption may be many times lower than declared.
• Very large number of strains with a low total CFU dose – mathematically impossible for each strain to be present in an effective amount.
• Promises to treat specific diseases – probiotics are dietary supplements, not medicines. A manufacturer who promises to "treat" IBS, Hashimoto's, or depression is violating the law and should inspire distrust.
• Lack of information on storage conditions – every reliable manufacturer specifies the temperature and duration for which the product maintains its declared shelf life.

6. Natural sources of probiotics and prebiotics in the diet

Probiotic supplements are a useful tool, but they cannot replace a well-balanced diet. Fermented foods provide live bacterial cultures in a natural food matrix, while vegetables, fruits, and whole-grain products provide prebiotics, without which the microbiome cannot function properly. Below is an overview of the most important sources – with specific data, not generalities.

6.1. Fermented dairy products – yogurt, kefir, buttermilk

Natural yogurt and kefir are the most widely available and best-researched sources of probiotics in the diet. However, their probiotic value depends on several conditions that are worth knowing before purchase.

Natural yogurt

Produced by fermenting milk with Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus – these are standard yogurt cultures required technologically. The problem is that both strains are relatively sensitive to stomach acid and may not survive in sufficient numbers to colonize the large intestine.

Some producers enrich yogurts with additional probiotic strains – e.g., Lactobacillus acidophilus or bifidobacteria – which increases their value. It is worth looking for the label "live bacterial cultures" and a list of specific strains.

Kefir

A fermented dairy drink with a richer microbiological profile than yogurt – produced using kefir grains, which are a symbiotic colony of several dozen species of bacteria and yeasts. It contains, among others, Lactobacillus kefiranofaciens, Leuconostoc spp. strains, and yeasts from the genera Saccharomyces and Kluyveromyces.

Kefir has a higher probiotic potential than typical yogurt and is better tolerated by people with lactose intolerance – fermenting bacteria break down a significant portion of lactose during fermentation.

Traditional buttermilk

A byproduct of butter production, containing lactic acid bacteria cultures. It is worth distinguishing it from industrially produced "buttermilk" made by acidifying milk without fermentation – the latter has no probiotic value.

6.2. Fermented foods – cabbage, cucumbers, kimchi, sourdough starter

Fermented foods are the oldest and most natural source of probiotics in the human diet. Lactic acid fermentation, which produces them, occurs without the use of baker's yeast or vinegar – solely thanks to lactic acid bacteria naturally present on the surface of vegetables. This makes fermented foods a product with an exceptionally rich and diverse microbiological composition.

Sauerkraut

A classic lactic acid fermentation product, containing mainly Leuconostoc mesenteroides strains (dominant in the early phase of fermentation) and Lactobacillus plantarum and L. brevis (dominant in mature sauerkraut). In addition to its probiotic value, sauerkraut is a rich source of vitamin C, lactic acid, and polyphenols.

Important note: sauerkraut must be raw and unpasteurized. Canned or jarred sauerkraut that has undergone heat treatment loses its live bacterial cultures.

Pickled cucumbers

Similar bacterial profile to sauerkraut, with a dominance of L. plantarum. It is worth distinguishing pickled cucumbers from gherkins (marinated in vinegar) – the latter do not contain live cultures and have no probiotic value. On the label: the ingredients of pickled cucumbers are only cucumbers, water, salt, and possibly spices. Vinegar in the ingredients means it's a gherkin.

How to pickle cucumbers yourself is described in the article Pickled cucumbers – step-by-step recipe and tips.

Kimchi

Korean fermented Napa cabbage, radish, and other vegetables, fermented with garlic, ginger, and chili. The bacterial profile is similar to sauerkraut – Leuconostoc spp. and Lactobacillus kimchii dominate. Kimchi provides both probiotics (fermented vegetables) and prebiotics (garlic, onion, ginger) – it is a natural form of synbiotic.

Beet kvass and fermented vegetable juice

Liquid form of fermented food, rich in lactic acid bacteria and lactic acid. Easy to incorporate into the diet as a drink or soup base.

Miso and tempeh

Fermented soy products popular in Asian cuisine. Miso – a paste made from fermented soybeans and rice or barley – contains live bacterial and fungal cultures, although heat treatment (e.g., cooking miso soup) destroys most of them. Tempeh – a block of fermented soybeans with the fungus Rhizopus oligosporus – is a rich source of protein and has a beneficial effect on the microbiome, although its probiotic profile differs from classic bacterial fermented foods.

Kombucha

Fermented tea drink produced using a symbiotic culture of bacteria and yeasts (SCOBY). It contains acetic acid, lactic acid, enzymes, and live microorganisms. The probiotic profile of kombucha is less homogeneous and more difficult to standardize than that of dairy products or fermented vegetables – the quality and microbiological composition vary significantly between manufacturers.

6.3. How to incorporate more prebiotics into your daily diet?

Most Poles consume too few prebiotics – the estimated daily intake is about 3–4 g, while the optimal amount is a minimum of 5–8 g. The difference is not large, but consistently maintained for years, it has a real impact on the composition of the microbiome and gut health.

Below is a summary of simple dietary changes that significantly increase prebiotic intake without drastic changes to the menu:

• Add raw garlic or leeks to salads and dressings – heat treatment destroys a significant portion of FOS; raw allium vegetables are the richest easily available source.
• Replace white rice with cooked and cooled potatoes – cooling after cooking converts some of the digestible starch into resistant starch, which acts as a prebiotic.
• Introduce legumes 3–4 times a week – beans, lentils, chickpeas provide both resistant starch and FOS; soaking before cooking improves tolerance.
• Eat unripe bananas instead of ripe ones – a yellow banana with green ends contains several times more resistant starch than a fully ripe one.
• Replace instant oats with regular or rolled oats – oatmeal is a rich source of beta-glucans; "instant" versions have a lower glycemic index and fewer beta-glucans after grinding.
• Add a spoonful of ground flaxseed to yogurt or oatmeal – flaxseed contains pectins and other fibers with prebiotic properties.

6.4. How to combine probiotic and prebiotic sources in your daily diet?

The most effective strategy is to combine fermented products (source of probiotics) with vegetables and whole-grain products rich in fiber (source of prebiotics) in one meal or throughout the day. This is a natural form of synbiotic – the probiotic receives nutrients exactly when it needs them.

Several proven combinations:

• Natural yogurt with an unripe banana and oatmeal – probiotic + prebiotic in one breakfast.
• Groats with sauerkraut and legumes – a classic Polish combination that coincidentally is almost a textbook synbiotic.
• Salad with raw leeks or garlic with a natural yogurt-based dressing.
• Miso soup (paste added to cooled broth at approx. 60°C, not boiled with it) with added inulin-rich vegetables.

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7. Are probiotics safe? Side effects and contraindications

Probiotics have a very good safety profile in healthy adults and children – confirmed by years of use and data from thousands of clinical trials. However, this does not mean that they are entirely risk-free for everyone. There are several situations where probiotic supplementation requires caution or medical consultation, and knowing possible side effects helps distinguish a normal body reaction from a signal requiring attention.

7.1. Typical reactions at the beginning of supplementation

The most commonly reported ailments when starting probiotics are bloating, increased gas, and abdominal discomfort in the first few days of use. This is a physiological, not pathological, reaction – the gut microbiome adapts to the influx of new microorganisms, and the fermentation of prebiotics (if using a synbiotic or simultaneously increasing fiber intake) produces gas as a byproduct.

Such symptoms usually resolve spontaneously within 3–7 days. If they are severe, the dose can be reduced for the first 1–2 weeks, and then gradually increased. A similar strategy – gradual introduction – is recommended when incorporating large amounts of prebiotic-rich vegetables into the diet, especially Jerusalem artichokes, garlic, and legumes.

Less commonly reported reactions include mild nausea or loose stools in the first few days – especially with multi-strain preparations in high doses. These symptoms also usually resolve spontaneously.

7.2. When can probiotics be risky?

Although serious side effects from probiotic use are rare, medical literature describes cases where live microorganisms posed a real threat. The risk is almost exclusively associated with specific clinical conditions – it practically does not occur in healthy individuals.

Severe immunodeficiencies

In patients after organ transplants, receiving immunosuppressive therapy, with advanced AIDS, or after chemotherapy – the introduction of live microorganisms carries a risk of bacteremia or fungemia (bacteria or yeasts entering the bloodstream). Documented cases mainly involve Lactobacillus strains in extremely immunosuppressed patients and Saccharomyces boulardii in patients with a central catheter. The absolute risk is low, but real in this group.

Premature infants and newborns with very low birth weight

This is a specific clinical situation – the intestinal barrier of newborns born before 32 weeks of gestation is immature, and the risk of bacterial translocation is higher than in older children and adults. At the same time, there are studies suggesting a benefit of probiotic therapy in preventing necrotizing enterocolitis (NEC) in premature infants – the decision to use should be made solely by a neonatologist.

Acute pancreatitis

This is a rare but significant contraindication. The PROPATRIA clinical trial (Netherlands, 2008) showed a higher risk of complications and mortality in a group of patients with severe acute pancreatitis who were given probiotics. The mechanism is not fully understood, but this study unequivocally excluded probiotics from treatment in this condition.

Structural heart defects and artificial heart valves

Isolated cases of bacterial endocarditis associated with Lactobacillus spp. have been reported in patients with valvular defects. The risk is extremely low, but cardiac surgery patients should inform their doctor about probiotic use.

7.3. Probiotics in children – what you should know?

In healthy children, probiotics have a good safety profile confirmed in numerous clinical studies. The best-studied pediatric strain is Lactobacillus rhamnosus GG – used in studies in infants, toddlers, and school-aged children without significant adverse effects.

Indications for which probiotics in children have the strongest evidence base:

• Antibiotic-associated diarrhea – as in adults, LGG and S. boulardii are the strains with the best clinical documentation.
• Acute infectious diarrhea – meta-analyses indicate a reduction in the duration of rotavirus diarrhea by approximately 1 day with the use of LGG.
• Infant colic – Lactobacillus reuteri DSM 17938 in drops has shown in several studies a reduction in crying time in breastfed infants, although results in formula-fed infants are less clear.
• Prevention of atopic dermatitis – probiotic supplementation in pregnant women at risk of atopy and in infants may reduce the risk of developing atopic dermatitis, although the effect depends on the strain used and the timing of the intervention.

Dosage in children differs from that in adults and depends on age and indication. Manufacturers of pediatric products usually provide adjusted dose ranges – adult products should not be used in children without verifying the dose.

7.4. Probiotics and medications – what interactions to avoid?

Interactions between probiotics and medications are relatively rare, but some are worth knowing:

Antibiotics. As described in section 4.1 – antibiotics can eliminate introduced probiotic strains. Maintaining at least a 2-hour gap between an antibiotic and a probiotic is standard advice. An exception is Saccharomyces boulardii – as a yeast, it is naturally resistant to bacterial antibiotics and can be taken simultaneously.

Immunosuppressive drugs. When using cyclosporine, tacrolimus, methotrexate, or other immunosuppressive drugs, probiotic supplementation requires consultation with the treating physician – see section 7.2.

Antifungal drugs. Fluconazole and other azole antifungal drugs can inhibit the growth of Saccharomyces boulardii – their simultaneous use reduces the effectiveness of this strain.

Apart from the situations mentioned, probiotics do not show clinically significant interactions with most commonly used medications – including drugs for hypertension, statins, antidiabetic drugs, or hormonal contraceptives.

7.5. Side effects of prebiotics – when is "too much of a good thing" harmful?

Prebiotics are generally safe, but their tolerance is individual and dose-dependent. The main adverse effects are bloating, gas, and intestinal discomfort at excessively high doses or when introduced too quickly into the diet. This results from rapid fermentation by gut bacteria and the production of gases (mainly hydrogen and carbon dioxide).

Prebiotic tolerance is particularly important in:

• Irritable Bowel Syndrome (IBS) – people with IBS often tolerate fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) poorly, which include FOS and inulin. The low-FODMAP diet, used in IBS, paradoxically limits the consumption of some prebiotics. In this group, prebiotics should be introduced particularly cautiously and in small doses.
• Inflammatory Bowel Disease (IBD) – in active inflammation of the large intestine or Crohn's disease, large amounts of fermentable fiber can exacerbate symptoms. The decision to supplement with prebiotics should be consulted with a gastroenterologist.
• Fructose or sorbitol intolerance – FOS contains fructose as a monomer; people with fructose intolerance may react to large doses of FOS or inulin.

8. Frequently Asked Questions about Probiotics and Prebiotics

8.1. Can probiotics be taken long-term?

Yes – in healthy adults, long-term probiotic supplementation is safe and does not cause addiction or "laziness" of one's own microbiome. The gut microbiome does not stop functioning independently under the influence of regular external probiotic supply.

However, it is worth distinguishing between two scenarios. For a specific clinical indication – e.g., antibiotic-associated diarrhea or IBS – supplementation makes sense for a defined period, after which the effects are evaluated. For prophylactic use, as general microbiome support, long-term supplementation is justified, provided it is based on a product with documented strains. The most important thing is not to treat supplementation as a substitute for a diet rich in fermented products and prebiotic fiber.

8.2. Do prebiotics work without probiotics?

Yes – prebiotics work independently of probiotic supplementation, because their role is to nourish bacteria already present in the gut, not those supplied externally. Every person has their own established microbiome, which benefits from prebiotics regardless of whether they take probiotics.

In practice, this means that increasing dietary prebiotic intake – through allium vegetables, legumes, oats, or resistant starch – makes sense as an independent health strategy, even without parallel probiotic supplementation. However, simultaneous use of both produces a synergistic effect, especially after antibiotic therapy or during microbiome reconstruction after dysbiosis.

8.3. How much time should pass between an antibiotic and a probiotic?

The recommended interval is at least 2 hours. An antibiotic taken too close to a probiotic dose can eliminate the introduced bacteria before they reach the large intestine. An exception is Saccharomyces boulardii – as a yeast, it is naturally resistant to bacterial antibiotics and can be taken without a time interval.

Probiotic therapy should be started as soon as possible after the first dose of antibiotic – without waiting for the end of the course – and continued for at least 1-2 weeks after its completion. The microbiome needs time to rebuild, and probiotics help shorten this period and reduce the risk of post-antibiotic dysbiosis.

8.4. When to take probiotics – on an empty stomach or with food?

It depends on the strain and the form of the preparation, but the general rule is: most probiotics are best taken just before or during a meal. Food buffers stomach acidity and shortens transit time through the low pH environment, which improves bacterial survival. A study published in Beneficial Microbes (Tompkins et al., 2011) showed significantly higher survival of Lactobacillus and Bifidobacterium strains when administered with a fat-containing meal compared to administration on an empty stomach.

Exception: Probiotics in enteric-coated capsules are designed to survive the acidic stomach environment regardless of the time of consumption – the timing of administration is less critical for them. Saccharomyces boulardii is naturally resistant to stomach acid and can also be taken regardless of meals.

8.5. How many CFU should a good probiotic have?

There is no single universal answer, as the optimal dose is strain-dependent and determined by clinical trials for specific applications. In practice, most well-researched preparations fall within the range of 1-20 billion CFU daily – and this dose is sufficient for the vast majority of indications in healthy adults.

More important than the number of CFUs itself is whether the dose is guaranteed until the expiration date (not just on the day of manufacture) and whether the specific strain has been clinically tested at a similar dose. A product with 50 billion CFUs of unidentified strains is less valuable than a product with 5 billion CFUs of a well-researched strain with a specified code.

8.6. Do probiotics help with Helicobacter pylori infection?

Probiotics do not replace eradication antibiotic therapy for H. pylori infection – this is causal treatment and there is no alternative. However, several clinical studies have shown that adding selected probiotic strains to the standard treatment regimen can reduce the severity of therapy side effects (diarrhea, nausea, dysbiosis) and slightly increase the rate of successful eradication.

The best-documented auxiliary strains in H. pylori therapy are Lactobacillus reuteri DSM 17938, Saccharomyces boulardii CNCM I-745, and selected multi-strain preparations with Lactobacillus and Bifidobacterium. The decision to include a probiotic in eradication therapy should be discussed with the treating physician.

8.7. Are probiotics safe during pregnancy and breastfeeding?

Available data indicate that probiotic use during pregnancy and lactation is safe for healthy women. No adverse effects for the mother or fetus have been reported with the most commonly studied strains – Lactobacillus rhamnosus GG, L. acidophilus, Bifidobacterium lactis – at standard doses.

Furthermore, probiotic supplementation in the third trimester of pregnancy and early breastfeeding is the subject of research as a strategy to reduce the risk of atopic dermatitis in children at risk of atopy. Despite the good safety profile, as with any supplementation during pregnancy, it is advisable to inform the treating physician about the preparations being used.

8.8. How quickly do probiotics and prebiotics change the microbiome?

The first measurable changes in microbiome composition appear relatively quickly – studies using DNA sequencing show changes after just 1-2 weeks of regular probiotic supplementation or increased prebiotic intake. An increase in the number of bifidobacteria with inulin or FOS supplementation is visible after 2-3 weeks.

A key caveat: changes caused by supplementation are largely temporary. After discontinuing probiotics or returning to a fiber-poor diet, the microbiome gradually returns to its baseline state – usually within a few weeks. Permanent changes in microbiome composition require permanent dietary changes. Supplementation is an effective short- to medium-term tool, but it does not replace a long-term nutritional strategy.

9. Summary

Probiotics and prebiotics are two different tools serving the same purpose – a healthy gut microbiome. A probiotic is a live microorganism, a prebiotic is a food substance that nourishes it. Together they form a synbiotic; the product of their joint action are postbiotics – metabolites with a wide range of effects on the body.

Key takeaways to remember:

• The strain matters. Probiotic properties are a characteristic of a specific strain, not a species. A product without a full three-part name and strain code cannot be verified in clinical studies.
• Indication determines choice. For antibiotic-associated diarrhea, you reach for LGG or S. boulardii. For IBS – for B. infantis 35624 or L. plantarum 299v. For intimate flora problems – for L. rhamnosus GR-1 and L. reuteri RC-14. A single "one-size-fits-all" product does not exist.
• Diet is fundamental. Probiotic supplementation yields temporary effects – the microbiome returns to baseline if the diet remains poor in fiber and fermented products. Pickled foods, kefir, allium vegetables, legumes, and oats are the foundation without which no supplement will have a lasting effect.
• Safety is high, but not unconditional. In severe immune deficiencies, acute pancreatitis, and selected clinical situations, probiotic supplementation requires medical consultation.
• CFU and number of strains are not everything. Fewer strains in a higher dose with full names are better than a long list without codes and in a dose too low to show clinical effect.

The gut microbiome is one of the most dynamically researched areas of modern medicine. Knowledge about it is changing rapidly – some of today's recommendations will be revised or refined in a few years. What is already certain is that a diet rich in diverse plant products and fermented foods is the most effective long-term investment in gut health – regardless of how further research on probiotics develops.

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