Leaves from the tree llex paraguariensis are steeped in hot (but not boiled water) and the resulting infusion is drunk as a hot beverage called Maté (or Chimarrão) in Paraguay, Uruguay, Argentina and Brazil. Currently the branches, including the bark, are discarded, generating large amounts of solid waste. Now Brazilian researchers have found that extracts of the bark are high in the phenolic compounds epigallocatechin gallate and chlorogenic acid.
Epigallocatechin gallate is a catechin or flavanoid also found in green tea and has been subject to a number of theriputic drug trials (Wikipedia link at end of the story). Chlorogenic acid is found in peach, prunes and coffee, and has been shown to reduce the rate of glycogen conversion to glucose and to decrease glucose absorption in the body, which could help in weight control. Indeed, it is marketed in Great Britain and Sweden under the name Svetol as a slimming product.