A gut feeling

Pre, pro, post, it is enough biotics to make you go bonkers. You may not have heard of postbiotics, but if you consider the names of its more famous family members – and you are familiar with the rules of suffixes in the English language – you can probably make a deduction. But first, let us remember the good reasons to know the background behind the biotics.

Since the very early days of Hippocrates and his theory of the four humours, we have known that our food choices have had an impact on our health. “Let thy food be thy medicine and thy medicine be thy food,” as the mythologised quote goes. As though in accordance with this philosophy, we are currently undergoing a cultural reappraisal of the complementarity of nutrition and pharmacology. Our growing prioritisation of food for health is having a huge impact on consumer choices too, with 70% in a survey for the International Food Information Council (IFIC) saying they consumed yoghurt for its health and wellness benefits over its taste profile.

According to Grandview Market, the global probiotics market size is estimated at $77.12bn in 2022 and is expected to grow at a compound annual growth rate (CAGR) of 14% from 2023 to 2030. Meanwhile, the global postbiotic supplements market was valued at $10.7m in 2022 and is anticipated to reach $24.3m by 2030. It may sound considerably smaller than its familiar-sounding sibling but take into account that postbiotics are still in their early days of research; if you have not figured out those suffixes yet, it would be a healthy time to learn.

To bring everyone up to speed, probiotics are live microorganisms, mostly bacteria but sometimes some fungus as well. Prebiotics, on the other hand, essentially serve as the food for probiotics and are found in foods like garlic and bananas. Humans are not able to digest these prebiotic fibres. Rather, prebiotics are digested and used as food by the probiotics and other gut microbiota in the lower digestive tract.

From waste to wellness

By now, you have likely deduced that postbiotics are generated after digestion. They are the metabolites, the by-products or you could even say waste produced during the digestion of prebiotics and fibre-rich compounds by probiotics, in the gut’s resident microbiota. This occurs in the colon, the lower part of the digestive system, during colonic fermentation. Here, non-digestible prebiotic and fibre substances in our food are broken down by gut microbiota, producing beneficial compounds for our health like short-chain fatty acids, certain vitamins (vitamins B and K), amino acids and antimicrobial peptides that prevent the growth and activities of harmful bacteria.

“Postbiotics is a really new topic in this sort of family,” describes Senaka Ranadheera, senior lecturer of food processing and preservation at the University of Melbourne, Australia. “I mean, it’s been like 100 years, 110 years or so since the first sort of formal definition of probiotics. Even, in the early, very early ages, people knew that fermentation could bring some health benefits.” Renanadheera, a food scientist who has focused his research on probiotics and prebiotic food applications for more than a decade, explains that it is only been with the recent developments of techniques that we have been able to isolate and identify postbiotics and begin to understand their potential uses.

So far, it is generally understood that postbiotics are beneficial by-products for us and can even provide the same benefits as probiotics. Critically, however, they can provide these benefits without any side effects that pro and prebiotics can have. “Probiotics are very individual-specific, strainspecific. For example, some probiotics might work really well with my system, but they might not work within you; they’re very individualised,” Ranadheera says. “For certain people, consumption of probiotics can be a bit uncomfortable, not like very detrimental or really critical but things like gas and bloating.” Instead, postbiotics can offer as a beneficial alternative for those who cannot tolerate consuming probiotics and prebiotics, without any known risks.

Indigestible definitions

One of the well-known benefits of postbiotics is their ability to boost the gut microbiome and support healthy activities, growth and functions of probiotics – in fact, this “health-promoting effect” of postbiotics is the very definition that the International Scientific Association of Probiotics and Prebiotics (ISAPP) uses to define a postbiotic. “So, basically, they react by flourishing the beneficial microorganisms in our system,” adds Renanadheera. This regulation and promotion of gut microbiota activities plays a pivotal part in maintaining overall good health. “We know [postbiotics] stimulate our immune system, they can fight against bad pathogenic microorganisms,” Renanadheera notes. One example is the exopolysaccharides produced by Lactobacillus delbrueckii ssp. Bulgaricus – one of the starter culture bacteria used to produce yoghurt – which has even been shown to enhance the activity of the body’s natural killer cells.

Renanadheera’s research has also found postbiotic short-chain fatty acids produced by the digestion of fibre-rich plant foods can also lower the risk of colon cancer. These cancer-protective metabolites, as they are considered, have shown some positive effects on breast cancer patients, too. In summary, the authors of the comprehensive review, ‘The clinical evidence of postbiotics as microbial therapeutics’ published in Gut Microbes, also concluded: “There is growing evidence for the clinical benefits of postbiotics in the management of highly prevalent conditions including gastrointestinal, dermatological and neurological disorders as well as respiratory infections and metabolic syndrome. Postbiotics may offer a novel therapeutic approach for these conditions.”

However, it is important to remember that it is still early days for postbiotic research and much of what has been conducted so far has been cellularbased lab experiments or performed on animals. In fact, the concept of postbiotics is still so relatively new, that the process of defining them remains a work in progress. In an article in Nature Review, Renanadheera was among the authors who contested the aforementioned definition from the ISAPP. Key to their objection was that under the ISAPP’s term, postbiotics would be grouped with inactivated microorganisms or dead probiotics and their products. Recent research has shown that even if the probiotic cells are removed completely from their growth medium – for example, the food source that the probiotics are grown in – the cellfree source can still produce some positive effects, including boosting the immune system. This is because some postbiotics are produced in the food, even if all living probiotics have been removed, for example, some exopolysaccharides and vitamins remain active and do not degrade in food before they are consumed.

Renanadheera and his team, however, argue that grouping these dead probiotics with probiotic by-products under one definition would generate confusion. “So, are they probiotics or postbiotics? Because probiotics need to be living at the time of consumption, but what about if you consume dead probiotics in your yoghurt? They’re not metabolites.” While the exact perimeters of the definition are still being defined, Renanadheera and much of the scientific community are convinced of their benefits to support the body’s immune system. It is this grey area of dead probiotics, moreover, that Renanadheera seems to believe will be where the next big breakthrough will occur.

When asked if he thinks we understand the full extent of the benefits of postbiotics, Renanadheera is adamant: “No, not yet; we have no idea.” For now, all we know is that it is generally advised that the best thing to do for gut health is to continue eating probiotic containing foods, such as cottage cheese and sauerkraut. This is because they contain both the postbiotics that are produced during fermentation as well as living probiotics, which will continue to release more postbiotics into the gut. This synergistic potential is another reason Renanadheera advocates for consuming postbiotics through diet rather than supplements – as he also points out that this combination of biotic benefits is often more time and cost-efficient, too.

“Now, we know that gut microorganisms have a significant effect on a person’s health outcome, [and] gut microbes by microorganisms are very closely associated with probiotics, prebiotics, and now postbiotics,” Renanadheera explains. As scientists like himself continue to talk in support of the gutbrain axis, it is as though we are returning to those very early ideas of Hippocrates; except this time, we are armed with more knowledge and technology to understand how to harness the very best of our food. “We didn’t know about postbiotics before, but now, bit by bit via unveiling and discovering new things. Maybe [in the] next ten years, we might discuss certain other compounds as well,” Renanadheera concludes. “New things are always coming into, but this is really, really exciting for me as a probiotics researcher.” And after hearing from him, this enthusiasm for postbiotics is hard not to share.