SAN FRANCISCO - Sugar producers think recent marketing efforts by manufacturers of high-fructose corn syrup aren't so sweet.

In a lawsuit filed last week, three sugar distributors say that equating HFCS with real sugar -- with slogans like "your body can't tell the difference" -- misleads consumers.

They accuse defendants, including Archer Daniels Midland Co (ADM.N) and Cargill [CARG.UL], of using the publicity campaign to offset growing customer concerns about obesity.

"This suit is about false advertising, pure and simple," said Inder Mathur, CEO of Western Sugar Cooperative, one of the plaintiffs.

Audrae Erickson, president of the Corn Refiners Association, said the lawsuit is without merit, as HFCS and sugar are nutritionally and metabolically equivalent.

"Sugar is sugar," Erickson said.

The United States is the biggest consumer and manufacturer of high-fructose corn syrup, with soft-drink makers the largest users.

The sweetener was added to beverages such as Coca-Cola in the early 1980s, but U.S. food makers have been edging away from it in recent years, trying out a return to sugar in some products after studies linked corn syrup to obesity.

However, HFCS has been able to regain market share recently amid surging sugar prices. [ID:nL3E7DK0BJ]

The Corn Refiners Association has asked federal regulators to allow HFCS to be called "corn sugar." But the lawsuit says the defendants "jumped the gun" and started using the term before receiving approval.

Erickson said the Corn Refiners Association will "vigorously" defend its right to petition for the name change with the U.S. Food and Drug Administration.

"We stand by the message in our ads and the science behind it," Erickson said.

The case in U.S. District Court, Central District of California is Western Sugar Cooperative et al. v. Archer Daniels Midland Co et al, 11-3473.

(Reporting by Dan Levine; Editing by Tim Dobbyn)