Grocery shoppers examining colorful packages bearing long lists of hard-to-pronounce ingredients might take comfort in the belief that those substances were deemed safe by the government.

They might also believe that some federal agency must, at least, be notified when a new substance enters the U.S. food supply.

But that's not the case.

Over the past 15 years, the vast majority of new ingredients added to U.S. food never received a safety determination from the government. And since 1958, at least 1,000 legally entered the food supply without the knowledge of government officials, according to the Pew Health Group.

The U.S. Food and Drug Administration acknowledges that since 1997, it has largely transferred the responsibilities for pre-market safety determinations on ingredients — including flavorings, preservatives, texturizers and binders — from its own scientists to food manufacturers.

The agency characterizes the move as a "pragmatic means to protect health and avoid wasteful use of government and industry resources" at a time when government funding for FDA staffing in this sector is scarce.

But in recent years, a range of experts, advocates and groups, including Pew, the Government Accountability Office and the American Heart Association, have expressed concern about what they see as a lack of oversight and a potential public health threat.

James T. O'Reilly, author of definitive texts on U.S. food and drug law, said he believes the 1997 policy changes put consumers at greater risk.

"I can confidently tell you there is no other area of food law in the developed world that is so badly regulated as this corner of the U.S. food system," he said.

Many industry representatives, however, say the system is working. In the July issue of the journal Food and Drug Policy, Ray A. Matulka, of the food safety consulting firm Burdock Group, responded to recent criticism of the program.

"FDA currently has sufficient authority to evaluate the safety of food ingredients (whether notified to FDA or not) and take the necessary course of action to maintain the safety of food and food ingredients," he wrote.

He characterized recent calls by Pew, the GAO and the heart association to overhaul the program as "an agenda-driven cadre of interest groups."

If a manufacturer wants to introduce a new ingredient to the food supply, it does not need to alert the FDA. But it does need to determine the ingredient is safe, meaning there is "reasonable certainty in the minds of competent scientists that the substance is not harmful under the intended conditions of use," according to the law. In the jargon of the FDA, this would make it a GRAS ingredient: generally recognized as safe.

What troubles some is that "competent scientists" can be employees or contractors of the product's manufacturer.

Manufacturers can — and many do — present their safety information on a new ingredient to the FDA as part of a voluntary notification program. The agency then examines the company's safety determination and issues a letter of "no questions" or "insufficient basis."

But even when the FDA does examine safety determinations, at no point does it affirm the safety of the product. In fact, it specifically notes in each letter that the agency has "not made its own determination of the GRAS status."

O'Reilly calls this a "yo-yo" letter, meaning: "You're on your own."

In 2010, the GAO issued a report criticizing government oversight of new ingredients, urging the FDA to strengthen its oversight of GRAS determinations, conduct random audits of manufacturers' safety assessments and address conflicts of interest between manufacturers and scientists hired for safety reviews.

At minimum, the report said, the FDA should require companies to submit basic information — including the name of substance, intended uses and scientists who evaluated it — when they put it on the market.

To Lisa Shames, director for food safety and agriculture at the GAO, this information void is one of the most troubling aspects of the process. "The FDA doesn't know what it doesn't know," Shames said. "It simply has no idea how many self-affirmed GRAS food substances have been introduced into the food supply."

The FDA indicated general agreement with the GAO recommendations but has never enacted changes in response to the report.

Last year, the Pew Health Group added to the debate by publishing a report with estimates on the number of substances the FDA has reviewed (7,000) since 1958, those it hasn't (3,000) and those it has never been notified about (1,000). These include ingredients added directly to food but also indirect ingredients, which come into contact with food during processing and in packaging.

Pew plans to publish more studies in coming months focusing on how other countries treat U.S. GRAS ingredients and how the program deals with conflicts of interest between scientists and manufacturers, among other topics.

Although Pew researchers acknowledge that the 1997 rule change encouraged more manufacturers to submit notifications about new ingredients to the FDA, very few of those manufacturers ask for an FDA review, preferring to make their own determinations. The change also limits the opportunity for the public to provide input on new ingredients.

"The FDA no longer writes specific regulations for the use of the substance or puts those rules up for public comment by consumers, academics and competitors," said Tom Neltner, who heads the Pew Health Group project.

The GAO report noted that a few substances initially considered GRAS have later been found to pose health risks and were subsequently banned by the FDA. The most recent of these decisions was in 1986, when the FDA prohibited the use of sulfites as a preservative on raw produce due to severe allergic reactions in those sensitive to sulfites.

The GAO investigated the GRAS system at the request of Congress in 2010, and Pew formed a group to dig further shortly after that. More recently, the heart association joined the GRAS debate as part of its effort to reduce salt consumption.

Earlier this year, the heart association presented a 19-page statement to the FDA on salt, asking the agency to modify salt's GRAS status and set limits on its safe use in products. The letter also called on the FDA to strengthen the GRAS process, noting that it currently "relinquishes too much of the agency's authority to food manufacturers and does not do enough to ensure the safety of substances that are added to food."

Those who favor the FDA's current approach often point to the power of the marketplace as form of regulation: Unsafe ingredients are bad for the bottom line.