SALT LAKE CITY — On stage at a sales convention, XanGo executive vice president Joseph Morton said that when he first stumbled across mangosteen, a tropical fruit with purported curative powers, "I didn't have to have it confirmed in the New England medical journal before I would listen."

Morton apparently was referring to the prestigious New England Journal of Medicine. Morton's Xango, a multilevel marketing company, has built a huge business around its mangosteen-based juice, which it promotes as an immunity booster.

The company still hasn't proved its health benefits — which it says could include a stronger immune system and improved joint function — to skeptical experts. XanGo's Web site includes a disclaimer, noting the juice is not meant to treat or prevent disease.

A lab test arranged by The Associated Press found its antioxidant power to be on par with other fruit juices.

Morton, 37, was on a business trip in Malaysia when he saw mangosteen, a white fruit wrapped in a blood-red leathery shell, on the dessert menu.

From that introduction, Morton and his business partners capitalized on a new brand category of liquid "super-fruits" that is "doing gangbusters," said Jeff Hilton, a partner at Integrated Marketing Group, a branding and packaging consultant.

LOTS OF COMPETITION

XanGo has more than two dozen competitors that sell fruit juices, powdered drinks and vitamin fizz tablets. Tahitian Noni International Inc. sold $2 billion worth of noni juice, from the French Polynesian fruit, in its first 10 years by 2006. MonaVie, also of Utah, bottles a blend of acai juice from the Amazon basin berry. Pure Fruit Technologies Inc. underprices XanGo on a mangosteen-based juice that sells in health food stores.

XanGo, a private company that doesn't reveal financial statements, said at the October convention that since its launch five years ago, sales of the mangosteen-based juice topped a cumulative $1 billion. It ships bottles by the case from Spanish Fork, Utah, and says it has 700,000 unsalaried sales associates in 17 countries.

"That's the only product they sell, and people are taking it around the world," said Sen. Orrin Hatch, R-Utah, who quaffs the purplish-colored juice and pops multivitamins and other supplements every day.

Hatch was the prime sponsor of the 1994 Dietary Supplement Health and Education Act, which allows the sale of supplements unless the Food and Drug Administration can prove them harmful.

An independent lab test performed for The Associated Press shows XanGo's antioxidant strength is no better than other readily available fruit juices, yet it costs nearly $40 a bottle. XanGo insists mangosteen contains other beneficial chemicals.

"My big concern with XanGo is that the business has gone a long way without showing any benefit in human trials," said Wayne Askew, director of the Division of Nutrition of the University of Utah's College of Health.

Others are skeptical, too.

"It's a 'Wizard of Oz' story," said Anthony Almada, president and chief executive of GENr8 Inc., a marketer of sports nutrition dietary supplements. "The industry is built on storytelling, and because they do it one-on-one, without advertising, they don't incur the wrath of the FDA."

TEST RESULTS

Dietary supplements are a $22 billion, largely unregulated business in the U.S.

For the lab test, The Associated Press shipped a 750-milliliter bottle of XanGo to Oregon State University's Linus Pauling Institute at Corvallis. The institute measured its antioxidant strength against store-bought juices that sell for a few dollars a bottle.

On a scale of molecular weight, XanGo's antioxidants measured 14,884 micromoles per liter — slightly higher than cranberry juice, but lower than black cherry and less than half that of blueberry juice. Apple juice finished last in this test.

"In terms of its antioxidant capacity, XanGo is in the middle of the pack," said Balz Frei, the institute's director and chairman.

Antioxidants are substances added to many foods and even soap in the belief they can slow down the damage oxidation can do to cells.

Frei and other scientists emphasize that antioxidants haven't been shown to actually work inside the human body. Antioxidants are known to work in test tubes, but stomach acids could neutralize them before they can get to work destroying any cell-damaging free-oxygen radicals.

Uncertainties over testing protocols have stalled research, yet every day seems to bring another mangosteen bottler, as an Internet search will show.

XanGo's research and development manager insists mangosteen has more to offer than its so-called oxygen radical absorption capacity — a cocktail of other chemicals barely known to science.

"You have a fruit that's very complicated, with a lot of chemicals in it," said Mike Pugh, who dismissed antioxidant ratings as a "numbers game" He said the type of antioxidants can be more important.

Pugh believes all the scientific debate can be pointless: If mangosteen makes people feel better, he said, it must do some good.

XanGo has been warned by the FDA for claiming that mangosteen could ward off disease or cancer. The company insists those claims were printed by a third party on a brochure at a recruitment seminar and that it's not responsible.