Rising U.S. sales of acai, a purple Amazon berry promoted as a "superfood" on Oprah Winfrey's Web site, are depriving Brazilian jungle dwellers of a protein-rich nutrient they've relied on for generations. U.S. consumers are turning "a typical poor people's food into something like a delicacy," said Oscar Nogueira, who specializes in the fruit at Embrapa, Brazil's agricultural research company. Spending on acai-based products by Americans seeking to lose weight, gain energy or slow aging doubled to $104 million last year, according to SPINS, a Schaumburg, Ill.-based market research firm. Since U.S. demand took off early this decade, the fruit's...