Banks’ pullback from commodities trading is weakening the link between raw materials and equities and helping to re-establish supply and demand as the main factor in setting prices, United Nations researchers say.

As Barclays Plc, JPMorgan Chase & Co. and Morgan Stanley leave parts of the business, prices of commodities are moving more independently of stocks. The correlation between U.S. equities and corn, cattle and wheat fell to less than 0.05 in January, compared with almost 0.3 in 2008, an analysis by David Bicchetti and Nicolas Maystre, economic affairs officers at the UN Conference on Trade and Development in Geneva, shows.

Banks, hedge funds and other financial institutions piled into physical commodities and derivatives over the past 12 years, amplifying a run-up in prices for everything from copper to oil, in short supply before the 2008 global recession, the UN found in a 2011 study. The exodus is nudging futures markets back toward their original function, as a way for farmers, miners and other companies in the commodities business to hedge against price swings.

“Now, we’re getting back to where strict supply-demand gives us truer pricing and hopefully better ability to look ahead,” Richard Nelson, chief strategist at Allendale Inc., a broker and consultant in McHenry, Illinois, said in an April 21 phone interview. For people who use the contracts to hedge, “it’s a completely good thing,” he said.

The weaker correlation with stocks also restores commodities’ appeal as a way for investors to diversify, according to Citigroup Inc. A correlation of 1 would mean prices moving in lockstep.