This was Dr. D's question/answer post a couple of weeks ago (I didn't include the footnotes--have to go to the q&a if you are interested in them):
TYPE O AND YERBA MATE
QUESTION: I'm an O+ who quit drinking coffee and started drinking Yerba Mate.
Never felt better. Soothes my stomach. Is it advisable?
ANSWER: Yerba mate, or Ilex paraguariensis is a South American holly tree that
provides the leaves and stems from which a popular hot drink is brewed. In traditional cultures the tea is usually drunk from a hollowed out gourd which can be lavishly decorated with silver, or aluminum or just left plain. Yerba mate means, in fact, "gourd tea." The straw-like utensil with which the tea is drunk is called a "bombilla."
It is used in popular medicine and employed in commercial herbal preparations as a stimulant to the central nervous system, a diuretic, and an antirheumatic (1). The plant also has a considerable amount of antioxidant activity. (2)
Arguments have been raised as to whether Yerba Mate is high in caffeine -or whether the particular xanthine in Yerba Mate, given the name 'matteine' has a different action on the body. Since many people feel that Yerba Mate enhances their sleep, this may well be true.
Studies have also shown that the plant does have the effect of dropping the
'repiratory quotient' indicating a rise in the proportion of fat oxidized. This appears to indicate that the plant has some potential in the treatment of obesity.(3)
Yerba mate also appears to block the oxidation of the so-called 'bad cholesterol" or LDL (5) On the down-side, there is some evidence that mate drinking may be associated with increased risks of aero-digestive cancers (4) though this may be an interaction between mate and other factors such as alcohol or tobacco smoking.
Can I make it a recommendation? Not really. Though I suspect that an occcasional
cup is fine as long as one controls for other lifestyle issues, such as excessive use of alchohol, or smoking.