In the East many traditional complementary and alternative medicines (TCAM) have flourished during the ages: traditional Chinese medicine (TCM), Unani, traditional Japanese medicine (TJM), Ayurveda, etc. Though less known, also in the West, one tradition has asserted itself: Western Constitutional Medicine (WCM). All these ancient medicines have a common denominator: the idea of constitution. Scientific studies have always been concerned with this idea and have tried to identify its features. Several theories have been advanced trying to explain the reality of constitutions, with various successes. Quite recently, a new concept has emerged from biology: the fact that humans are metaorganisms (holobionts).  This new way of looking at humans promises to change medicine forever. In this framework, the two forms of classification (WCM and ABO blood grouping) could be seen as not mutually exclusive and can merged into an alternative medical system.  On the one hand, the ABO blood type divides humanity into four basic blood groups: A, B, AB and O.  This typology is based on glyco-chemical markers or determinants which have been lately demonstrated to influence health and disease.  On the other hand, WCM four biotypes (air, water, earth and fire) have always been in the collective imagination of the West. The proposed new system of medicine defines 16 basic constitutions of individuals based on physical and genetic features. The ABO-WCM system merges ancient medicine of the West with contemporary biological medicine. The resulting new system can aid in identifying the susceptibility to diseases and the necessary dietary advice to exalt the characteristics of each unique human holobiont. In this way, the goal of personalized medicine becomes more easily achievable.