TORONTO (Bloomberg) - The Standard & Poor's/TSX Composite Index fell 15.21 points, or 0.1 percent, to 11,713.43. The S&P/TSX gained 3.7 percent this month as commodities rallied in response to stronger-than-forecast corporate earnings worldwide. The Thomson Reuters/Jefferies CRB Commodity Price Index advanced 6.1 percent this month, with copper surging 12 percent, the most in a year.

"How self-sustaining is this economy? That's what people are questioning," said Bob Decker, who helps oversee C$4.2 billion ($4.07 billion) as a money manager at Aurion Capital Management in Toronto. "No one disputes we've got a recovery in earnings. It's the sustainability of the recovery that's being questioned."

Canadian gross domestic product increased 0.1 percent in May, Statistics Canada said. Economists in a Bloomberg survey had estimated that economic growth climbed 0.2 percent, based on the median estimate in a Bloomberg Survey.

US GDP advanced at an annualised rate of 2.4 percent in the second quarter, the Commerce Department said in Washington, trailing the median economist estimate of 2.6 percent. The rate of increase in consumer spending eased from the first quarter.

The S&P/TSX Energy Index retreated for a fourth day, due largely to Canadian Oil Sands, which had its 12-month unit-price estimate cut to C$31 from C$34.50 by TD analyst Jeff Meunier.

Canadian Oil Sands dropped 2.2 percent to C$26.96. Nexen Inc., an oil and gas producer with operations on five continents, declined 1.2 percent to C$21.35. Canadian Natural Resources Ltd., Canada's second-largest energy company by market value, lost 1.1 percent to C$35.40.

Five of the six largest publicly traded Canadian banks declined. TD decreased 1.1 percent to C$73.16.

Royal Bank of Canada, the country's largest bank, slipped 0.6 percent to C$53.72. Canadian Imperial Bank of Commerce, the No. 5 bank by assets, retreated 0.6 percent to C$70.60.

RIM rose for a third day, gaining 2.6 percent to C$59.15 after Bloomberg News reported it will introduce a "Blackpad" tablet.

The company's worldwide smartphone shipments increased the most among the top five handset makers in the second quarter, researcher Strategy Analytics said yesterday.

First Quantum Minerals Ltd., the second-largest Canada- based copper producer, sank 4.5 percent to C$64.42, adding to yesterday's 4.7 percent slump. A parliamentary committee in Zambia has called for the reintroduction of a windfall tax on copper sales above $2.50 a pound, UBS AG analyst Onno Rutten said in a note to clients.

Viterra Inc., Canada's largest grain handler, fell 4.2 percent to C$8.05 after competitor GrainCorp Ltd. agreed to buy AWB Ltd. for A$803 million ($723 million). The purchase may help GrainCorp challenge Viterra and Cargill Inc. for market share in Asia.