Bill Gross who runs the world's biggest bond fund at Pacific Investment Management Co., said structural headwinds may reduce real economic growth below 2 percent in the U.S. and other developed nations.

"The biblical metaphor of seven years of fat leading to seven years of lean may be quite apropos in the current case with the observation that the developed world's growth binge has been decades in the making," Gross wrote in his monthly investment outlook posted on the Newport Beach, California-based company's website today. "We may need at least a decade for the healing."

With globalization, technological and demographic changes restricting growth, investors should seek returns from commodities such as oil and gas, U.S. inflation-protected bonds, high-quality municipal debt and non-dollar emerging market stocks, Gross said, reiterating earlier recommendations.

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