Postbiotics – Definition, Effects and Applications

What Are Postbiotics?

Postbiotics are a group of bioactive substances that arise as metabolic by-products when beneficial gut bacteria (probiotics) break down dietary fibres and other food components (prebiotics). They can be thought of as the end products of microbial fermentation in the gut. Unlike probiotics, which contain live microorganisms, postbiotics consist of non-living bacterial components or their metabolic products.

The term has been formally defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) as: a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.

Types of Postbiotics

Postbiotics encompass a wide range of substance classes, including:

• Short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate – produced during the breakdown of dietary fibre and essential for gut health
• Bacterial cell wall components such as lipopolysaccharides, peptidoglycans, and teichoic acids
• Bacterial exopolysaccharides – sugar-based compounds with immunomodulatory effects
• Enzymes and proteins produced by gut bacteria
• Bacteriocins – antimicrobial peptides that inhibit the growth of harmful bacteria
• Vitamins such as B vitamins and vitamin K, synthesized by gut bacteria
• Tryptophan metabolites and other neurotransmitter precursors

Mechanism of Action

Postbiotics exert their effects through various mechanisms in the human body:

Influence on the Immune System

Postbiotics can modulate both the innate and adaptive immune systems. They interact with Toll-like receptors (TLRs) and other pattern recognition receptors on immune cells, leading to targeted regulation of inflammatory processes. This allows them to act both pro- and anti-inflammatory depending on the needs of the organism.

Protection of the Intestinal Barrier

Short-chain fatty acids, particularly butyrate, serve as the primary energy source for intestinal epithelial cells (colonocytes). They strengthen the integrity of the gut mucosa, promote the expression of so-called tight-junction proteins, and thereby reduce intestinal permeability (leaky gut syndrome).

Antimicrobial Effects

Bacteriocins and other antimicrobial postbiotics selectively inhibit the growth of pathogenic microorganisms in the gut without disrupting the beneficial gut flora.

Influence on Metabolism and the Nervous System

Certain postbiotics, such as tryptophan metabolites, can influence the production of serotonin in the gut and may therefore affect mood and well-being through the gut-brain axis. Short-chain fatty acids are also involved in regulating blood glucose and lipid metabolism.

Medical Applications

Research into postbiotics is still relatively young but has shown promising results in several medical areas:

• Gastrointestinal conditions: Irritable bowel syndrome, inflammatory bowel diseases (Crohn's disease, ulcerative colitis), diarrhoeal diseases
• Allergies and atopic conditions: Atopic dermatitis, allergic asthma, food allergies
• Metabolic disorders: Type 2 diabetes, obesity, metabolic syndrome
• Immune support: Prevention of respiratory tract infections, particularly in children and the elderly
• Mental health: Research into depression and anxiety disorders via the gut-brain axis
• Oncology: Potential preventive effects against colorectal cancer

Postbiotics in Supplements and Foods

Postbiotics occur naturally in fermented foods such as yoghurt, kefir, sauerkraut, kimchi, miso, and kombucha. These foods contain a combination of live microorganisms as well as their metabolic by-products.

In addition, postbiotics are increasingly available as targeted dietary supplements in the form of capsules, tablets, or powders. A key advantage over probiotics is their greater stability: as they contain no living organisms, they are more heat-resistant, have a longer shelf life, and do not require a cold chain.

Difference Between Pre-, Pro-, and Postbiotics

These three terms are often confused, but they describe distinct concepts:

• Prebiotics: Non-digestible food components (e.g., dietary fibres, inulin) that promote the growth of beneficial gut bacteria
• Probiotics: Live beneficial microorganisms (e.g., Lactobacillus and Bifidobacterium strains) that confer a health benefit when consumed in sufficient amounts
• Postbiotics: Non-living components or metabolic products of microorganisms that also confer a health benefit

Safety and Tolerability

Postbiotics are generally considered well-tolerated and safe. Because they contain no living microorganisms, there is no risk of infection from the administered bacterial strains – unlike with some probiotics. This makes them particularly interesting for immunocompromised individuals, premature infants, or critically ill patients in whom live probiotics may be contraindicated.

Adverse effects are rare and in individual cases may include mild gastrointestinal complaints such as bloating or stomach discomfort, particularly at the start of supplementation.

References

1. Salminen S. et al. - The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology and Hepatology, 2021; 18: 649-667.
2. Aguilar-Toalá J.E. et al. - Postbiotics: An evolving term within the functional foods field. Trends in Food Science and Technology, 2018; 75: 105-114.
3. Żółkiewicz J. et al. - Postbiotics - A Step Beyond Pre- and Probiotics. Nutrients, 2020; 12(8): 2189. DOI: 10.3390/nu12082189.