Jessica Stone·Nutritionist and digestive health writer. Connects the dots between your gut bacteria, immune system, and daily well-being in ways that actually make sense.·· min read
What Is a Postbiotic and Why Should You Care?
You have probably heard of probiotics, the live bacteria in yogurt and supplements. You may have come across prebiotics, the dietary fibers that feed them. But there is a third category that the research community has been building a solid case for: postbiotics.
Postbiotics are not a wellness marketing invention. In 2021, an international panel published a formal consensus definition in Nature Reviews Gastroenterology and Hepatology, placing postbiotics on equal scientific footing with probiotics and prebiotics [1]. The clinical trial literature has grown substantially since, and the results are worth understanding.
What a Postbiotic Actually Is
The International Scientific Association of Probiotics and Prebiotics (ISAPP) defines a postbiotic as "a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host" [1]. Two conditions are required. The microorganisms must be inactivated (non-viable), and the preparation must have documented health-promoting effects.
The word "inanimate" is key here. Postbiotics contain bacterial cells that have been killed, most often through heat treatment, along with the structural fragments and metabolites those cells carry. The inactivation method must be documented, because it affects what the postbiotic does [1].
Before the 2021 consensus, the same category had been called paraprobiotics, ghost probiotics, and tyndallized bacteria, among other terms, with no standardized definition. The ISAPP framework resolved that: health claims must now be tied to specific, characterized preparations rather than to postbiotics as a broad undifferentiated label [1].
A postbiotic preparation may include whole inactivated bacterial cells, cell wall fragments like lipoteichoic acid (LTA) and peptidoglycan, bacterial metabolites including short-chain fatty acids (SCFAs), exopolysaccharides, and functional surface proteins [9]. The composition depends on the strain and inactivation method, which is why two products labeled "postbiotic" can behave quite differently.
How Postbiotics Work in the Body
Frequently Asked Questions
This content is for informational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any supplement or making changes to your health regimen.
JS
Jessica Stone
Nutritionist and digestive health writer. Connects the dots between your gut bacteria, immune system, and daily well-being in ways that actually make sense.
Nutritionist and digestive health writer. Connects the dots between your gut bacteria, immune system, and daily well-being in ways that actually make sense.
postbioticsgut healthprobioticsmicrobiome
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The ISAPP panel identified five mechanisms through which postbiotics act [1]. Three show up most consistently across the clinical literature, and understanding them explains why non-living bacteria can produce meaningful health effects [9].
The first is epithelial barrier reinforcement. SCFAs, including butyrate, propionate, and acetate, upregulate tight junction proteins that seal gaps between intestinal cells, reducing how much inflammatory material crosses into circulation [9]. This pathway underlies postbiotic effects in both IBS and inflammatory bowel disease [11].
The second is immune modulation. Cell wall fragments from inactivated bacteria activate Toll-like receptors in immune cells, driving anti-inflammatory cytokines and sIgA production, and shifting systemic Th1/Th2 immune balance [9]. This is why postbiotics show effects in atopic dermatitis despite being a gut-based intervention [4].
The third is metabolic signaling. SCFAs bind to G-protein-coupled receptors (GPR41, GPR43, GPR109a) that regulate appetite hormones and insulin sensitivity, connecting postbiotic intake to outcomes beyond the digestive system including metabolic syndrome [10].
Who the Research Supports
Clinical evidence for postbiotics spans several distinct populations. The strength of that evidence varies by condition, but a few groups stand out as having direct trial-level support.
People with irritable bowel syndrome (IBS) have the strongest data. A multicenter, double-blind, placebo-controlled RCT in Lancet Gastroenterology and Hepatology enrolled 443 IBS patients who received heat-inactivated Bifidobacterium bifidum MIMBb75 at 10 billion cells per day (10⁹ cells/day) for eight weeks [2]. The composite primary endpoint was achieved by 34% on the postbiotic versus 19% on placebo (risk ratio 1.7; p=0.0007; number needed to treat approximately 6.6), with no serious adverse events in the treatment group.
Infants are a second population with meaningful evidence. A 2024 meta-analysis covering nine RCTs and 2,065 participants found postbiotic-supplemented infant formula to be safe, with no significant GI symptom increase and a significant rise in stool sIgA (P less than 0.05) [3]. Because postbiotics carry no live bacteria, they eliminate the infection risk that makes clinicians cautious about live probiotics in neonates.
Adults prone to colds have direct RCT evidence as well. A 24-week, double-blind, placebo-controlled trial gave 183 healthy adults 50 billion heat-killed Lacticaseibacillus paracasei MCC1849 cells per day [7]. The postbiotic group had significantly fewer days with stuffy nose, sore throat, and cold-like symptoms (p less than 0.05), with no reported adverse effects. Children with atopic dermatitis are another evidence-supported group: a network meta-analysis across nine RCTs found Lactobacillus rhamnosus IDCC 3201 reduced symptom scores (SMD negative 0.53; SCORAD MD negative 5.52) with adverse events no different from placebo [4].
What the Clinical Numbers Show
Looking at the postbiotic evidence as a body reveals what is well-established and what is still developing. The IBS RCT [2] is the clearest proof that non-viable bacteria produce clinically meaningful GI benefits: a 443-patient multicenter design with 34% versus 19% achieving the composite endpoint (risk ratio 1.7; number needed to treat approximately 6.6) provides solid Level 2 evidence.
The infant formula meta-analysis [3] adds population-level safety reassurance. Pooling nine RCTs and 2,065 participants, with no significant adverse event difference and a significant sIgA increase, matters for parents and clinicians weighing early nutrition options. The immune maintenance RCT [7] fills in the picture for healthy adults: 50 billion cells per day for 24 weeks, zero adverse effects, and significant reductions in cold symptom days.
A systematic review of 11 studies covering 477 participants found preliminary signals that postbiotics support mood stability, reduced fatigue, and athletic readiness over periods ranging from 13 days to 12 weeks [6]. Those findings are early-stage and larger trials are needed, but they hint at applications well beyond gut health. For context on how gut interventions connect to broader metabolic outcomes, the overview at probiotics for blood sugar covers related evidence.
Reviews on metabolic syndrome have identified specific inactivated strains, including heat-inactivated L. amylovorus CP1563 and B. animalis subsp. lactis CECT 8145, with evidence for improvements in body composition and metabolic markers [10]. That growing evidence base shows how the postbiotic research field is expanding beyond its original IBS and immunity focus.
Safety and Side Effects
The safety profile of postbiotics across published clinical trials is consistently favorable. Because they contain no live microorganisms, they eliminate the risks that live probiotics carry: no bacterial translocation, no antibiotic resistance gene transfer, and no sensitivity to concurrent antibiotics [8][9].
The clinical trial record bears this out. The IBS RCT recorded zero serious adverse events, with 91% rating tolerability as "very good" or "good" [2]. The infant formula meta-analysis found no significant adverse event difference across nine RCTs [3]. The 24-week immunity trial in 183 adults reported no adverse effects [7].
Where adverse effects have appeared, they are mild and infrequent. A systematic review of atopic dermatitis trials detected mild adverse effects in only 1 of 9 included RCTs [5]. Pediatric trials show adverse event rates equivalent to placebo, with the leading strain showing a risk ratio of 0.97 (95% CI 0.79 to 1.21) [4].
One caveat is worth noting. Older heat-killed Lactobacillus acidophilus LB formulations were linked to rare severe GI events in pre-2020 infant trials, which is why blanket safety assumptions across all formulations are not warranted [3]. The ISAPP consensus is explicit that health claims should be tied to specific characterized preparations, not to the postbiotic category as a whole [1]. Speaking with a healthcare provider before starting use is advisable, particularly for infants, immunocompromised individuals, or people managing chronic conditions.
Postbiotics vs. Probiotics: Practical Differences
The distinction between postbiotics and probiotics is not about one being superior in an absolute sense. It is about which option fits the situation better.
Stability is the most immediate practical difference. Live probiotics require refrigeration to maintain viability and can lose potency during warm storage or transit. Postbiotics have no viability requirement, so they can be shelf-stable with documented lifespans of up to five years [8]. That matters in warm climates, during travel, and for anyone who does not consistently refrigerate supplements.
Antibiotic compatibility is a second factor. Antibiotics target live bacteria, including those in probiotic supplements, but postbiotics are unaffected by concurrent antibiotic use since there are no viable cells to eliminate [8][12]. This makes them a practical option during or after an antibiotic course.
The immunocompromised population distinction is a third consideration. Live probiotic use carries a documented risk of bacteremia in severely immunocompromised individuals, while postbiotics carry no such risk [9]. For transplant recipients, patients on chemotherapy, or those with primary immune deficiencies, postbiotics are the biotic option with no viability-related infection concern. For a deeper look at how probiotic categories can work together, the synbiotics guide covers the evidence on combined approaches [12].
Frequently Asked Questions
Q. What is the difference between a postbiotic and a probiotic?
Probiotics are live microorganisms that confer a health benefit in adequate amounts. Postbiotics are preparations of non-viable (inactivated) microorganisms and/or their components that also confer a health benefit, without any live bacteria [1]. Key practical differences include stability (postbiotics do not require refrigeration and can last up to five years), antibiotic compatibility (they are not inactivated by concurrent antibiotic use), and safety in immunocompromised populations where live bacteria carry theoretical infection risk [8].
Q. Do postbiotics actually work, and what does the evidence say?
For several specific conditions, the clinical evidence is meaningful. An RCT in 443 IBS patients found heat-inactivated B. bifidum MIMBb75 achieved the composite primary endpoint in 34% versus 19% on placebo (p=0.0007; NNT approximately 6.6) [2]. A 24-week RCT in 183 adults found significant reductions in cold-like symptom days with no adverse effects [7]. Meta-analyses confirm safety and immune benefits in infants [3]. The strongest evidence covers IBS, infant immunity, atopic dermatitis, and respiratory immune maintenance.
Q. Are postbiotics safe for infants and children?
Current evidence is reassuring. A meta-analysis of nine RCTs involving 2,065 infants found no significant increase in serious adverse events or GI symptoms with postbiotic-supplemented infant formula, and documented a significant sIgA increase (P less than 0.05) [3]. Pediatric atopic dermatitis trials show adverse event rates equivalent to placebo [4]. The specific preparation and strain matter, and guidance from a pediatrician is appropriate before use in infants.
Q. Can postbiotics be taken with antibiotics?
Unlike live probiotics, postbiotics are not affected by concurrent antibiotic use. They contain no viable bacteria for antibiotics to target, removing the timing concerns that apply to live probiotic supplementation [8][12]. Some researchers have investigated postbiotics as a specific option during antibiotic courses, when live probiotic viability is compromised, though larger trials are still needed in this area.
Q. Is there a standard dose for postbiotics?
There is no universal dose, because efficacy is strain-specific and preparation-specific [1]. Clinical trials have used 10 billion inactivated cells per day for IBS over eight weeks [2] and 50 billion heat-killed cells per day for immune maintenance over 24 weeks [7]. Products where the strain, inactivation method, and dose match published trial conditions are more straightforward to evaluate than those using generic postbiotic labeling.
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. DOI: 10.1038/s41575-021-00440-6
[2] Andresen V, Gschossmann J, Layer P, "Heat-inactivated Bifidobacterium bifidum MIMBb75 (SYN-HI-001) in the treatment of irritable bowel syndrome: a multicentre, randomised, double-blind, placebo-controlled clinical trial," Lancet Gastroenterology and Hepatology, 2020. DOI: 10.1016/S2468-1253(20)30056-X
[3] Liang X, Li Y, Zhao Z et al., "Safety and efficacy of adding postbiotics in infant formula: a systematic review and meta-analysis," Pediatric Research, 2024. DOI: 10.1038/s41390-023-02813-w
[4] Tan Lim CSC, Sajo MEJ, Orteza KEMP et al., "Next-Gen biotherapeutics: A systematic review and network meta-analysis on postbiotics as treatment for pediatric atopic dermatitis," Pediatric Allergy and Immunology, 2023. DOI: 10.1111/pai.14022
[5] Lima M, Paulino LC, "Oral Postbiotics as a Therapeutic Strategy for Atopic Dermatitis: A Systematic Review of Randomized Controlled Trials," Journal of the American Nutritional Association, 2024. DOI: 10.1080/27697061.2023.2232021
[6] Kerksick CM, Moon JM, Jager R, "It's Dead! Can Postbiotics Really Help Performance and Recovery? A Systematic Review," Nutrients, 2024. DOI: 10.3390/nu16050720
[7] Sato S, Arai S, Iwabuchi N et al., "Effects of Heat-Killed Lacticaseibacillus paracasei MCC1849 on the Maintenance of Physical Condition in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study," Nutrients, 2023. DOI: 10.3390/nu15153450
[8] Mosca A, Abreu Y Abreu AT, Gwee KA et al., "The clinical evidence for postbiotics as microbial therapeutics," Gut Microbes, 2022. DOI: 10.1080/19490976.2022.2117508
[9] Ma L, Tu H, Chen T, "Postbiotics in Human Health: A Narrative Review," Nutrients, 2023. DOI: 10.3390/nu15020291
[10] Bourebaba Y, Marycz K, Mularczyk M, Bourebaba L, "Postbiotics as potential new therapeutic agents for metabolic disorders management," Biomedicine and Pharmacotherapy, 2022. DOI: 10.1016/j.biopha.2022.113138
[11] Wang S, Wang P, Wang D et al., "Postbiotics in inflammatory bowel disease: efficacy, mechanism, and therapeutic implications," Journal of the Science of Food and Agriculture, 2025. DOI: 10.1002/jsfa.13721
[12] Smolinska S, Popescu F-D, Zemelka-Wiacek M, "A Review of the Influence of Prebiotics, Probiotics, Synbiotics, and Postbiotics on the Human Gut Microbiome and Intestinal Integrity," Journal of Clinical Medicine, 2025. DOI: 10.3390/jcm14113673
This content is for informational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any supplement or making changes to your health regimen.
