Postbiotics are byproducts of natural probiotic (good) bacteria fermentation. Postbiotics help growth and survival of good bacteria in the gut, help reduce inflammation, mimic effects of probiotics, kill pathogens, regulate hormone and insulin levels, and boost immunity. They are regarded as a good addition to probiotic supplements.
A 2019 study summery: “Research to date indicates that postbiotics can have direct immunomodulatory and clinically relevant effects and evidence can be found for the use of postbiotics in healthy individuals to improve overall health and to relief symptoms in a range of diseases such as infant colic and in adults atopic dermatitis and different causes of diarrhea”. (Postbiotics and Their Potential Applications in Early Life Nutrition and Beyond (nih.gov)
Below I have included a link to good article on postbiotics:
South Korea already makes nutritional supplements with postbiotics and they are available on ebay: Postbiotics | eBay