*2.6.1 SCFAs*

They are produced by the intestinal fermentation of dietary fiber, non-starch polysaccharides (NSP), and resistant starch, mainly in the proximal part of the large bowel, in relationship with the substrates and the microbiota. The most important SCFAs are represented by acetic acid (AA), propionic acid (PA), and butyric acid (BA), and a proper SCFA ratio helps the immune system. Also, they have the capacity to acidify the environment, which is considered by some researchers to be beneficial by improving the bioavailability of metals and by protecting against the pathogenic bacteria, but harmful by others due to the supposed damage of the intestinal mucosal barrier [87–90].
