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Since you've already addressed the overinflated claims (and prices) of noni and acai, I'm wondering about your opinion of mangosteen products (e.g. Xango).
Frankly: noni has a horrible flavour, but mangosteens are delicious, and I get them fresh where I live (Honduras). The same people who touted noni juice are now on the mangosteen bandwagon, though, but it all just seems like more "snake oil" and "patent medicine" to me.
I will admit to not having eaten mangosteen, but I have heard that it is pretty tasty. You are right about the "snake oil" claims for these juices. They may be high in antioxidants, but so are most fruits. We do know that juices are not the best way for getting your antioxidants: better to eat the fruit itself. If you have a choice, you will always be better off having the real thing rather than juice.
Have blueberries, strawberries, blackberries, figs, pears... any fruit is going to be great for you. (But you're right, it should taste good.)
Thanks for writing,
Timothy S. Harlan, MD, FACP