The Food and Drug Administration yesterday announced a new regulation that will allow manufacturers of diet supplements wide leeway in making health claims for their products.

Some consumer advocates expressed dismay that the FDA's "final regulation" appeared to back away from earlier, tougher proposals on label claims, and suggested that the rule could sow further confusion among supplement users.

"The marketplace will be flooded with thousands of products claiming to treat every ailment known to man," said Bruce Silverglade, legal affairs director for the Center for Science in the Public Interest. "For the average consumer this regulation puts them back in 19th century--'buyer beware.' "

The new rule, which will take effect Feb. 5, marks the latest round in the FDA's ongoing and often acrimonious efforts to enact effective regulations to cover the booming diet supplement industry.

Under the 1994 Dietary Supplement Health and Education Act, supplement companies may market new products without prior FDA approval, as long as they do not claim to prevent, treat or cure a disease.

The companies are free to make claims about how their products affect the "structure or function" of the human body. Thus, "treats insomnia" is a "disease claim," while "helps you relax" is a "structure/function" claim, even though they relate to the same condition.

Quarrels over this distinction have provoked frequent conflicts between the FDA and the supplement industry, and some court cases. The new regulation was designed to "clarify" the difference by "setting up criteria and providing a large number of examples," said Margaret Dotzel, the FDA's acting associate commissioner for policy.

Dotzel also acknowledged that the FDA narrowed the definition of "disease" after sifting through the "thousands of comments from industry, consumers and consumer groups" that came in after the agency first proposed a rule last year: "We did think some of the concerns were valid," Dotzel said. "Our [new] criteria will only capture disease claims."

The Grocery Manufacturers of America, an industry group, praised the new regulation. "We applaud FDA for moving in the right direction and correcting the problem concerning the scope of the definition of the term 'disease,' " said Stacey Zawel, the group's vice president for scientific and regulatory policy, in a statement.

Silverglade, however, scoffed at the FDA for softening its position after "industry dumped thousands of letters on its doorstep."

While the vast majority of products marketed as diet supplements are either helpful or harmless, reports persist of adverse reactions to unregulated products that may contain powerful drugs that in synthetic form can only be obtained with a prescription.