Garcinia Cambogia extract (GCE) comes from a tropical fruit grown in India and Southeast Asia. The active ingredient has been identified: hydroxycitric acid (HCA). It is said to block fat and suppress the appetite. It inhibits a key enzyme, citrate lyase, that the body needs to make fat from carbohydrates. It suppresses appetite by increasing serotonin levels; low serotonin levels are associated with depression and emotional or reactive eating.