What are Probiotics, Prebiotics, and Postbiotics? A Guide to Gut Microbiota Health

  Gut health has been at the center of scientific interest in recent years, and for good reason. Trillions of microorganisms inhabit the human digestive system, collectively forming the gut microbiota. The gut microbiota participates in digestion, immune system regulation, the synthesis of certain vitamins, and even communication with the brain via the so-called gut-brain axis¹. The balance between "good" and potentially harmful microorganisms is crucial for maintaining health. When this balance is disrupted, we speak of gut dysbiosis. Dysbiosis (microbiota imbalance) is linked to a range of conditions, including:

• inflammatory bowel diseases,
• metabolic syndrome,
• allergies,
• mood disorders, etc.

Although causality is still being investigated, there is increasing evidence that microbiota modulation through diet, prebiotics, and probiotics can play an important preventive and supportive role². In this context, probiotics, prebiotics, and increasingly - postbiotics are often mentioned. Although the terms are similar, their roles are distinct yet interconnected. In this article, we provide a scientifically-based explanation of their synergy and importance for the body.  

1. Probiotics - Good Bacterial Cultures

According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host³. For a microorganism to be considered a probiotic:

• it must be clearly identified at the strain level,
• safe for use, and
• have a proven effect in clinical trials³.

They most commonly belong to the genera Lactobacillus, Bifidobacterium, and the yeast Saccharomyces boulardii. These microorganisms are naturally present in a healthy gut microbiota, but their representation can be reduced due to stress, improper diet, infections, antibiotic use, medications, etc.

How do probiotics work?

Probiotics act through several complementary mechanisms:

1. Competitive inhibition of pathogens: probiotic strains can bind to the intestinal epithelium, thereby preventing the adhesion of potentially pathogenic microorganisms. They also produce antimicrobial substances such as bacteriocins and organic acids that lower pH and hinder the growth of harmful bacteria³.
2. Strengthening the intestinal barrier: certain probiotic strains promote the production of mucin and tight junction proteins, thereby contributing to the integrity of the intestinal barrier and reducing intestinal permeability⁴.
3. Modulation of the immune system: probiotics can influence the activation of dendritic cells, macrophages, and lymphocytes, and regulate the balance between anti-inflammatory and pro-inflammatory cytokines³. This contributes to the maintenance of immune homeostasis.
4. Metabolic activity and fermentation: in cooperation with prebiotics, probiotics participate in the fermentation of indigestible carbohydrates, producing short-chain fatty acids (SCFAs), including butyrate, acetate, and propionate⁵.

In what conditions are probiotics used?

Numerous studies have investigated the effects of probiotics in various conditions:

• Prevention and alleviation of antibiotic-associated diarrhea: a meta-analysis published in JAMA showed that probiotics reduce the risk of diarrhea associated with antibiotic use⁶.
• Irritable Bowel Syndrome (IBS): a systematic review and meta-analysis indicate that probiotics can reduce overall IBS symptoms, including pain and bloating⁷.
• Immune support: certain strains are associated with a reduction in the frequency of respiratory infections and modulation of the immune response³.

How to choose a quality probiotic? What to look for?

1. Strain-specific action One of the most important characteristics of probiotics is the fact that their effects are strain-specific. This means that a health effect proven for one bacterial strain cannot be automatically attributed to another strain, even within the same species³. For example, different strains within the genus Lactobacillus or Bifidobacterium may have different effects on digestion, the immune system, or the intestinal barrier. Therefore, when choosing probiotic formulations, it is crucial to check if the declaration states the exact strain name (e.g., a combination of genus, species, and strain designation) and to verify if there is scientific documentation supporting its use. 2. Number of live microorganisms (CFU) and survival through the digestive system

The efficacy of probiotics also depends on a sufficient number of live microorganisms, most often expressed in colony-forming units (CFU).

It is also important that the microorganisms survive passage through the acidic environment of the stomach and reach the intestines in an active form³. Quality formulations use technological solutions that increase the stability and resistance of bacteria, such as protective capsules or microencapsulation. 3. Combination of multiple strains and synergy with prebiotics Modern approaches to probiotic formulations often include a combination of multiple strains in appropriate concentrations. Such a combination can provide complementary effects, for example, simultaneous support for the intestinal barrier and immune regulation. Additionally, the combination of probiotics with prebiotics (so-called synbiotics) can increase the effectiveness of their action. Prebiotics provide a substrate for the growth of beneficial bacteria, stimulating their metabolic activity and the production of short-chain fatty acids like butyrate. This achieves their synergistic effect.  

2. Prebiotics – Nutritious fibers for good bacteria

Prebiotics are substrates selectively utilized by host microorganisms conferring a health benefit⁸. Unlike probiotics, which are live microorganisms, prebiotics are most often indigestible dietary fibers or their derivatives that pass intact through the small intestine and reach the large intestine, where they become a food source for beneficial bacteria. The best-researched group of prebiotics are fructans, which include inulin and fructooligosaccharides (FOS). Although chemically related, they differ in chain length, fermentability, and clinical effects. They are not digestible in the small intestine but reach the large intestine where they serve as "food" for beneficial bacteria.

How do prebiotics work?

Prebiotics work in the following ways:

1. Selective stimulation of beneficial bacteria: prebiotics promote the growth and activity of bifidobacteria and lactobacilli, which is known as the "bifidogenic effect"⁹. This contributes to microbiota balance and reduces space for potentially harmful microorganisms.
2. Increased production of short-chain fatty acids (SCFAs): the fermentation of prebiotics produces SCFAs: acetate, propionate, and butyrate; which have important metabolic and immunological roles⁵.
3. Regulation of intestinal function: prebiotics increase stool volume, improve consistency, and can contribute to regular digestion⁹.

When probiotics and prebiotics are used together, we speak of synbiotics. The goal is to improve the survival and activity of beneficial microorganisms by providing an appropriate substrate for their growth¹⁰. Such a combination can increase the colonization of beneficial bacteria, stimulate the metabolic activity of the microbiota, and enhance the production of beneficial metabolites.

What are FOS (fructooligosaccharides) and inulin? Similarities and differences

Both FOS and inulin belong to the fructan group, but they differ in polymer chain length: FOS have shorter chains (usually 2–10 fructose units) while inulin has longer chains (up to 60 or more units). This difference affects the speed of fermentation, tolerability, and metabolic effects. Key advantages of FOS are:

• Faster and more selective fermentation: due to its shorter chain length, FOS ferments more quickly in the large intestine, resulting in more efficient and predictable stimulation of bifidobacteria⁸. This pronounced bifidogenic effect is well-documented in clinical studies.
• Better tolerability at lower doses: although both FOS and inulin can cause bloating at higher doses, FOS is often used in lower, more precisely defined quantities that allow for achieving the effect with less gastrointestinal discomfort⁹.
• Faster effect on the microbiota: a shorter chain also means a faster metabolic response of the microbiota. This can be especially important in situations where faster modulation of gut balance is needed, for example, after antibiotic therapy.
• Synergy with probiotics: due to its rapid fermentability, FOS serves as a suitable substrate for probiotic strains, thereby supporting their activity and SCFA production¹⁰.

The key value of prebiotics is not only in promoting the growth of beneficial bacteria but in the creation of their metabolic products, especially butyrate. The availability of fermentable substrates directly affects the amount of SCFAs produced⁵. In this way, prebiotics represent the foundation for the creation of postbiotics and indirectly influence the integrity of the intestinal barrier, immune regulation, and metabolic balance.  

3. Postbiotics and butyrate - key metabolic products

One of the most important results of the fermentation of prebiotics by probiotics is the production of short-chain fatty acids (SCFAs), among which butyrate (butyric acid) is particularly prominent. According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit on the host¹¹. In a broader sense, they also include metabolic products like SCFAs.

Butyrate - why is it important?

Butyrate has multiple biological effects:

• Main energy source for colon cells (colonocytes): up to 70% of the energy needs of colonocytes are provided by butyrate oxidation¹².
• Preservation of intestinal barrier integrity: butyrate promotes the expression of tight junction proteins, thereby contributing to the reduction of intestinal permeability⁴.
• Anti-inflammatory action: it acts as a histone deacetylase (HDAC) inhibitor, regulating the expression of genes involved in inflammatory processes¹².
• Immunomodulation: it promotes the differentiation of regulatory T-cells, important for controlling the immune response¹³.
• Metabolic effects: SCFAs are linked to the regulation of glucose and lipid metabolism⁵.

 

Conclusion

Prebiotics and probiotics act synergistically; the former feed beneficial bacteria, while the latter directly supplement the microbiota. Their interaction results in the creation of postbiotics like butyrate, a molecule with proven effects on the intestinal barrier, immune system, and metabolic health. Scientific evidence clearly points to the importance of maintaining a diverse and functional microbiota. The combination of carefully selected probiotic strains, prebiotic fibers, and key micronutrients represents a rational, scientifically based approach to supporting gut health, and thus the entire organism.   References:

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