Overview: The "Nutrient-Repositioning" -Unexpected Amino Acid Functions

Repositioning is usually used to indicate drug repositioning, or the finding of new disease applications for existing, approved drugs. Nutrients can be ingested for nutritional as well as therapeutic purposes, acting much the same as drugs. Amino acids are organic compounds that possess both amino and carboxy group functionalities and are best known as building blocks of proteins in living organisms. Recent studies of individual amino acids have revealed them to be functional ingredients of new therapeutics, promoting health in addition to nutrition. Here, we propose "nutrient-repositioning", the discovery of effects different from the existing effects of nutrients. This review summarizes some recent discoveries of unexpected amino acid functions, especially in BCAAs, histidine and serine.