It is not obvious how well probiotics fit the above description of dietary supplements. Probiotics can provide a variety of functions otherwise not available to the human host, including enzymatic activities uniquely capable of efficiently metabolizing complex compounds such as dietary fibers, mucins, bile acids etc. There are many mechanisms, including generation of short term fatty acids (SCFA) and interactions with host immune system, that have been suggested as beneficial functions of probiotics. However, such functions might already be provided in ‘nutritionally sufficient’ amounts by an individual’s commensal gut microbiota. It remains to be defined what exactly ‘nutritionally sufficient’ amounts of such microbial enzymatic activities and other functions or ‘adequate amounts’ of probiotics are.