Postbiotics – the underestimated active ingredients of the gut

Probiotics and prebiotics have long been part of everyday vocabulary. Microbiome research, however, has already moved a step further: postbiotics. These bioactive metabolic products of our gut bacteria work without any live germs — which makes them particularly stable and easy to control. Current studies suggest that postbiotics can influence the immune system, may play a role in defending against infections, and are even being studied in connection with metabolic health. A look at a still-young but fast-growing field of research.

What postbiotics actually are

Postbiotics are described in the scientific literature as bioactive compounds that form in a matrix during fermentation and may be beneficial to health. The term covers a range of substances: short-chain fatty acids (SCFAs), enzymes, peptides, teichoic acids, peptidoglycan fragments, polysaccharides, cell wall proteins and organic acids. Unlike probiotics, postbiotics contain no live microorganisms — only their metabolic products or cell components — which reduces the theoretical risk of unwanted immune reactions or bacterial translocation. A foundational 2020 review in the journal Nutrients puts it succinctly: because postbiotics contain no live microorganisms, the risks associated with them are minimised — a point that makes them potentially interesting for people with a weakened immune system, though individual suitability should always be assessed medically.

Through which channels postbiotics may act

A review published in October 2025 in the journal Infection, Genetics and Evolution describes in detail the immunomodulatory, anti-inflammatory and antimicrobial properties of postbiotics and the extracellular vesicles derived from them. Postbiotics are described as being able to intervene in immune regulation: they're associated with strengthening the epithelial barrier function, influencing the balance between Th1 and Th2 immune responses, and promoting regulatory T cells. Short-chain fatty acids such as butyrate, propionate and acetate — the best-studied postbiotics — also supply energy to gut lining cells and are linked to anti-inflammatory effects via certain signalling pathways in immune cells.

What is known about the so-called gut-lung axis

One particularly active area of research is the "gut-lung axis" — the observation that processes in the gut microbiome may also affect immune defence in the respiratory tract. The review mentioned above summarises preclinical findings on conditions such as pneumonia, influenza, COVID-19, asthma and allergic rhinitis: in animal and cell models, postbiotics strengthened the epithelial barrier, influenced the immune response, inhibited pathogenic biofilms and in some cases enhanced the effectiveness of conventional therapies. Important context: these are mostly preclinical findings; controlled human clinical trials for this indication are still lacking for most of the conditions mentioned.

What a recent study shows about postbiotics during antibiotic therapy

A randomised, placebo-controlled pilot study published in January 2026 in the journal Infection and Immunity examined 32 patients who received oral antibiotics and an oral probiotic for non-gastrointestinal infections. Half additionally received a fermentation-based postbiotic, the other half a placebo.

At the end of antibiotic treatment, the postbiotic group (n = 16) showed a 40% higher fecal bacterial alpha diversity than the placebo group (n = 16), as measured by the inverse Simpson index. Analysis of 157 longitudinally collected stool samples showed that this increase was mainly driven by enrichment of health-associated bacterial groups — particularly obligate anaerobic Firmicutes from the Lachnospiraceae family — while potentially pathogenic Escherichia/Shigella species remained reduced in the postbiotic-treated group, even ten days after the end of treatment. The treatment was well tolerated. As a small pilot study, this finding needs confirmation from larger trials before general recommendations can be drawn from it.

What a study shows about postbiotics and metabolic health

A randomised, double-blind, placebo-controlled pilot study published in January 2026 in the journal Nutrition examined the postbiotic pA1c®HI in 17 people with obesity, with and without prediabetes, over 12 weeks (1 × 10¹⁰ cells daily versus placebo). In the postbiotic group, HbA1c fell significantly by −0.22 percentage points compared with placebo, and diastolic blood pressure dropped by an average of −8.8 mmHg. Differences in body weight, BMI and body fat compared with placebo did not reach statistical significance, though trends pointed in the same direction. A post-hoc analysis of participants with prediabetes also suggested improvements in blood glucose, HbA1c and insulin resistance (HOMA-IR).

An honest assessment should note the study's funding: part of the author team is employed by, or holds a patent related to, the manufacturer of the postbiotic under study — a conflict of interest the authors themselves disclose and one that should always be kept in mind when evaluating manufacturer-linked studies like this. It's also a small pilot study (n = 17) whose results would need to be confirmed by larger, independent trials.

An ongoing study on postbiotics and mood

A randomised, double-blind, placebo-controlled trial currently under way in South Korea is examining the effect of a postbiotic on mood in adults. 52 participants aged 19 to 39 with elevated scores on a depression screening scale receive either a postbiotic or a placebo over eight weeks; outcomes measured include depressive symptoms, momentary mood, psychological stress, and gut microbiome composition. The trial is not yet complete, with results expected by the end of 2026 — an interesting approach, but one on which no conclusion about effectiveness can currently be drawn.

A look at basic research: immune modulation in an animal model

An animal study published in November 2025 in the journal BMC Veterinary Research examined the immunomodulatory properties of three heat-inactivated Lactobacillus strains in a zebrafish model. Fish fed postbiotics showed altered expression of immune genes (Il1β and Ifn-γ) and, after infection with viral haemorrhagic septicaemia virus, higher survival rates — particularly with the strains Lactiplantibacillus plantarum HA-119 and Lactobacillus helveticus HA-122. Histological examination showed no changes to the gut lining. Findings like these from animal models provide useful mechanistic clues but don't translate directly to humans.

Possible advantages over live probiotics

The scientific literature associates postbiotics with several potential advantages over live probiotics:

• Greater safety: no risk of bacterial translocation, infection or excessive immune reaction — a point especially discussed for immunocompromised people.
• Greater stability: longer shelf life and lower sensitivity to temperature, moisture and stomach acid.
• Clearly defined composition: precise chemical characterisation can support more accurate dosing and standardised quality.
• No horizontal gene transfer: without live bacteria, the theoretical risk of transferring antibiotic-resistance genes doesn't apply.

These are plausible, partly evidence-backed advantages — but they don't mean postbiotics fundamentally "replace" probiotics: for many indications, the evidence base for probiotics is considerably larger, and current research tends to treat the two approaches as complementary rather than competing.

Conclusion

Postbiotics are a young, active field within microbiome science. As bioactive metabolic products of gut bacteria, they're credited with immunomodulatory, anti-inflammatory and antimicrobial properties, without the theoretical risks of live germs. Early controlled human studies — for example on protecting the microbiome during antibiotic therapy or on metabolic health — deliver promising but still preliminary results from small samples. For many of the applications discussed, such as respiratory or mental health, the evidence so far comes mostly from preclinical models or ongoing trials. Anyone looking to support their microbiome broadly will find complementary options in a fibre-rich diet, fermented foods where appropriate, and — depending on individual circumstances — carefully chosen supplements.

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This article is intended for general information about postbiotics and the current state of research and does not replace medical advice, diagnosis or treatment. If you have health concerns, please consult a doctor or pharmacist.

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Sources

• Żółkiewicz J, Marzec A, Ruszczyński M, Feleszko W: Postbiotics—A Step Beyond Pre- and Probiotics. Nutrients. 2020;12(8):2189. doi: 10.3390/nu12082189 (PMC, Open Access)
• Fadaee M, Mahrooghi D, Lahouty M, Oskouei SA, Nezhadi J: Postbiotics and extracellular vesicles: mechanisms of action and clinical promise in respiratory infections and inflammation. Infect Genet Evol. 2025;135:105837. doi: 10.1016/j.meegid.2025.105837
• Schluter J, Jogia W, Matheis F, et al.: A retrospectively registered pilot randomized controlled trial of postbiotic administration during antibiotic treatment increases microbiome diversity and enriches health-associated taxa. Infect Immun. 2026;94(1):e00390-25. doi: 10.1128/iai.00390-25 (PMC, Open Access)
• Preliminary effect of the postbiotic pA1c®HI in glucose metabolism of obese individuals: A pilot, randomized, double-blind, controlled nutritional intervention. Nutrition. 2026. doi: 10.1016/j.nut.2025.112948 (author conflict of interest with the manufacturer disclosed)
• Effects of Postbiotics on Mood Disorders in Korean Adults. ClinicalTrials.gov (ongoing trial, results pending).
• Immunomodulating properties of postbiotics from lactobacilli in zebrafish. BMC Vet Res. 2025.