A postbiotic is a preparation of dead microorganisms or their structural components that delivers a measurable health benefit. Unlike probiotics, which are living bacteria, postbiotics contain no live organisms at all. They’re the newest member of the “biotics” family in gut health, formally defined by an international panel of scientists in 2021, and they’re showing up in a growing number of supplements and functional foods.
What Counts as a Postbiotic
The International Scientific Association for Probiotics and Prebiotics (ISAPP) established the working definition: a postbiotic is “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.” Two key requirements stand out. First, the preparation must contain dead microbial cells or pieces of them, such as cell wall fragments, surface proteins, or other structural parts. Second, it has to have a demonstrated health benefit. A random pile of dead bacteria with no proven effect doesn’t qualify.
One common misconception is that any metabolic byproduct of gut bacteria counts as a postbiotic. It doesn’t. Purified metabolites like butyrate, lactate, bacteriocins, and amino acids already have their own chemical names and established identities. While these compounds can be present in a postbiotic preparation, they alone aren’t enough to meet the definition. The preparation needs to retain some of the microbial biomass, whether that’s intact dead cells or fragments of them.
What’s Actually in a Postbiotic
Postbiotic preparations can contain a range of microbial materials. The most common include:
- Cell wall fragments: structural pieces from the outer shell of bacteria
- Bacterial lysates: mixtures created by breaking open bacterial cells
- Exopolysaccharides: complex sugars that bacteria produce on their surfaces
- Enzymes: proteins bacteria use to carry out chemical reactions
- Cell-free supernatants: the liquid left over after bacteria and yeast are removed from a culture, containing compounds they produced
On a supplement label, you won’t always see the word “postbiotic.” Instead, look for names like sodium butyrate, calcium butyrate, dried yeast fermentate, or heat-killed versions of specific bacterial strains. These are all forms of postbiotic ingredients, just marketed under more specific terminology.
How Postbiotics Differ From Probiotics and Prebiotics
The three “biotics” work at different stages of the same process. Prebiotics are fibrous foods that feed beneficial bacteria already living in your gut. Think of them as fertilizer. Probiotics are live microorganisms, found in fermented foods like yogurt, kimchi, and sauerkraut, that add helpful bacteria to your gut community. They crowd out harmful bacteria by competing for space and resources.
Postbiotics sit at the end of this chain. They’re what remains after bacteria have done their work: the structural remnants and byproducts of microbial activity. Your gut naturally produces postbiotics every time your resident bacteria break down fiber. But the supplement and food industries are now creating postbiotic preparations outside the body, using controlled fermentation processes followed by heat treatment or other methods to kill the microorganisms while preserving their beneficial components.
How Postbiotics Work in the Body
Postbiotics influence your health through several overlapping pathways. They help maintain gut barrier integrity, which is the tight seal between your intestinal lining and your bloodstream. When that barrier weakens, bacteria and toxins can slip through and trigger inflammation throughout the body. Components from dead microbial cells appear to reinforce this barrier.
They also modulate the immune system. Your gut houses roughly 70% of your immune cells, and postbiotic compounds interact directly with them. Cell wall fragments and surface proteins from dead bacteria can stimulate immune activity without causing infection, essentially training your immune system to respond appropriately. Research has linked these effects to reduced risk of several chronic conditions, including inflammatory bowel disease, type 2 diabetes, obesity, and cardiovascular problems.
Within the gut itself, postbiotics help maintain microbial balance by inhibiting the growth of harmful bacteria while encouraging beneficial species to thrive. This creates a more stable and diverse microbiome, which is consistently associated with better overall health.
Why Postbiotics Are Easier to Use Than Probiotics
Probiotics have a fundamental practical problem: they’re alive, and keeping them that way is difficult. Live bacteria are sensitive to heat, moisture, and time. They can die on the shelf, in transit, or in the acidic environment of your stomach before reaching your intestines. This makes manufacturing, shipping, and storing probiotic products a constant challenge.
Postbiotics sidestep all of this. Because the microorganisms are already dead, the preparations are environmentally resilient. They hold up under industrial processing conditions, tolerate temperature swings, and maintain their functional activity over a longer shelf life. They also carry no risk of infection, which matters for people with weakened immune systems who are sometimes advised to avoid live probiotics. This stability makes postbiotics easier to incorporate into a wider range of food products and supplements without specialized cold-chain storage.
Regulation and Safety
Postbiotics don’t have their own regulatory category in the United States. Like most supplement ingredients, they fall under existing FDA frameworks. If a postbiotic ingredient is added to food, it’s classified as a food additive and requires either premarket FDA approval or Generally Recognized as Safe (GRAS) status. Achieving GRAS status demands the same quantity and quality of scientific evidence as formal FDA approval, based on published scientific data and established scientific principles. Some postbiotic ingredients qualify through a long history of consumption in food.
In practice, this means the regulatory landscape is still catching up. Individual postbiotic ingredients may have GRAS status under their specific chemical names, but there’s no blanket approval for the category as a whole. The quality and evidence behind different postbiotic products varies widely, so the specific ingredient and the company behind it matter more than the “postbiotic” label on the front of the package.