First it was blueberries, then the pomegranate, and now the "superfood" of the moment is the açai berry, a fruit native to South America that is harvested from trees in the Amazon rainforest. In Brazil, Colombia and Suriname, açai (pronounced "ah-sigh-ee") has been used both medicinally and as a food  for hundreds of years. More recently, Americans have been gulping down gallons of açai juice in an effort to court good health.

One of the companies cashing in this trend is MonaVie, a juice that blends the potent açai berry with 18 other fruits-including grape, passion fruit, kiwi, pomegranate, banana, blueberry and cranberry. It's packaged in a chic wine bottle that retails for about $40 (although the products are sold only through multilevel marketing, not in stores). The MonaVie website includes links to several research studies that extol the antioxidant-rich virtues of the açai berry, but they are very careful not to make any outrageous health claims. According to the studies they cite, the açai berry outscores every other fruit and vegetable on the ORAC scale, a measurement which ranks the antioxidant activity of various foods. "The freeze-dried açai found in MonaVie has an antioxidant capacity that is 15 times higher than blueberries, and research has shown that drinking four ounces of MonaVie Active daily can help enhance your body's antioxidant capacity and ability to fight free radicals," explains a MonaVie spokesperson. (MonaVie, citing their proprietary formula, doesn't reveal how much açai juice is in their beverage.)

But even though the company is careful with any claims, it can't control what committed users have to say about the product. A quick Web search reveals numerous Web sites dedicated to praising the powers of drinking juice made from açai berries. The açai converts claim that the purple elixir can perform all manner of health miracles-improve stamina; make skin look younger; lower blood pressure; alleviate joint pain; eradicate hot flashes, migraines and gout; improve sleep; and help autistic children function better. And although MonaVie is one of the biggest names in the açai game, it's not the only player. Other açai products are available online (such as Viva! Açai, which sells for $24.95 for a 32-day supply), and the shelves at stores like Whole Foods hold other açai juices (such as Bossa Nova, which sells for $2.99 for a 10-ounce bottle, and Sambazon Açai, $2.69 for a 10.5-ounce bottle).

"If the açai berry can do even one quarter of the things the hucksters claim it can, then it will prove to be a great thing," says Brent Bauer, M.D., director of the complementary and integrative medicine program at the Mayo Clinic in Rochester, Minn. "At this point, açai falls into the category of intriguing but unproven. It may in fact turn out to be the superfood it's advertised to be, but first we need some solid scientific evidence that can only come from human clinical trials."

So far, most of the studies done on the açai berry have been done in the lab-analyzing the nutrient content of the so-called superfood. What is known is that the berry is packed with good stuff: antioxidants (including flavonoids similar to those found in red wine), amino acids, monounsaturated oleic acid, fiber, and phytosteroids. What all that means is that açai berries do have the potential to have several positive health benefits. These include anti-inflammatory effects (which could, in theory, help with arthritis pain), cancer prevention, improving elasticity of the arteries, and preventing cholesterol from oxidizing and adhering to the artery walls.

"It definitely has the potential to do lots of good things, and I do think there's something there, but we still don't know what happens when you concentrate it and give it to humans at doses many times stronger than what the natives in the Amazon have been consuming for years," says Bauer.

He brings up a historical example that he feels should be a cautionary tale for anyone willing to endorse something just because it looks promising: the beta carotene story. Beta carotene is a powerful antioxidant, and several epidemiological studies showed that people whose diets featured high levels of beta carotene had less cancer. When that news broke, health-conscious people started popping high doses of beta carotene. But when a large-scale human clinical trial was finally completed, it was found that in smokers, high levels of beta carotene actually increased the risk of cancer.

The bottom line? Most experts agree that the açai berry probably does qualify as a superfood (it's a favorite of health gurus like Dr. Mehmet Oz and Dr. Nicholas Perricone), thanks to its rich antioxidant and nutrient profile. But they remind consumers that there is no health magic bullet. "If you still smoke, drink, don't exercise and eat fast food, drinking a few ounces of açai juice every day isn't going to keep you healthy," says Bauer.