permissible amounts of live microorganisms for pharmaceutical preparations and medicinal prod- ucts (01/2011:50104). Despite this lack of specific European regulation, many postbiotics (as well as probiotics, prebiotics, synbiotics) are still being advertised or licensed as immune-stimulating substances (Yin et al., 2018). On the other hand, the Food and Drug Adminis- tration (FDA) in the USA has no recommendations focused on postbiotics, and their use refer to the rules that apply to the individual regulatory catego- ry chosen for a product in development, meaning that the intended usage, safety, and efficacy of the probiotic-product must all fulfil the requirements for the relevant regulatory category (Thorakkattu et al., 2022). Evidence supporting postbiotic utility in the food and pharmaceutical industries is provided by an increasing number of both in vitro and in vivo studies, of which the focus is on postbiotic for- mulations produced from different Lactobacillus and Bifidobacterium strains and, to a lesser extent, from Saccharomyces species. CURRENT CLINICAL TRENDS IN POSTBIOTIC RESEARCH
In vitro investigations (e.g., cell lines and test- tube assays) help with identifying the bioactives in the postbiotic mixtures, while confirming their potential antimicrobial, anti-inflammatory, immu- nomodulatory, anti-proliferative and antioxidant properties. The exact mechanisms and proposed benefits are then tested in in vivo systems that employ the use of experimental animal models (e.g., rats, mice, hamsters). In those studies, the animals frequently receive a dietary intervention with the postbiotic at a dose calculated per body weight, helping to mimic a human real-case sce- nario. The intervention is then compared with an- imals receiving a control diet with no postbiotic (Cuevas-González et al., 2020). Once the postbiotic’s clinical capabilities in im- proving health outcomes are confirmed in an ani- mal model, the preparation can be further studied in humans. Of note, the efficacy found in animal studies may not translate to humans. Human stud- ies, or clinical studies, are primarily focused on confirming the suitability and efficacy of the post- biotics based on evidence obtained in the previous in vitro and in vivo studies. Clinical studies investi- gating postbiotics, similar to animal experiments,
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