WASHINGTON (Reuters) - From pizzas and soups to deli meats, dips and hamburgers, Americans’ diets are often packed with salt. On Wednesday the Food and Drug Administration moved to cut average salt consumption by a third in an effort to reduce heart attacks and strokes.

A view shows the U.S. Food and Drug Administration (FDA) headquarters in Silver Spring, Maryland August 14, 2012. REUTERS/Jason

The agency issued draft guidelines for major food manufacturers and big chain restaurants designed to reduce salt in hundreds of products, with separate sodium reduction targets set for two and 10 years.

More than 70 percent of the salt in the average diet comes in the form of processed and prepared food. The FDA’s goal is to lower sodium in those foods and give consumers the choice to add salt later if they want to. Excess sodium raises blood pressure and is a leading risk factor for cardiovascular disease.

The goal is to cut average adult salt consumption from 3,400 milligrams a day to 2,300. The average American consumes almost 50 percent more sodium than recommended by most experts, the FDA said. (See sodium content in a typical meal .)

Many U.S. food companies, including Campbell Soup Co CPB.N, General Mills Inc GIS.N and Kraft Heinz Co KHC.O, have already cut salt levels to some extent in anticipation of the guidelines, which have been in the works since 2011.

The FDA said it looks forward to a robust discussion with the public and industry before finalizing the guidance. Susan Mayne, director of the FDA’s food safety and nutrition division, said the discussion is needed “to make sure we have the right targets.” She declined to predict when the guidance would be finalized.

The food industry is likely to challenge the FDA’s targets.

“Like others inside and outside of government, we believe additional work is needed to determine the acceptable range of sodium intake for optimal health,” Leon Bruner, chief science officer at the Grocery Manufacturers Association, the industry’s biggest lobbying organization, said in a statement.

“This evaluation should include research that indicates health risks for people who consume too much sodium as well as health risks from consuming too little sodium,” Bruner added.

The agency has divided the affected food into 150 categories. Each will have different sodium targets, and some products will have more room for reductions than others. The agency singled out salad dressing as an example, saying the amount of sodium ranges from 150 mg per hundred grams to more than 2,000. Wheat bread ranges from 220 mg to 671 mg, it said.

‘SUBSTANTIAL BENEFITS’

The FDA’s proposal received support from Dr. Tom Frieden, director of the Centers for Disease Control and Prevention.

“Scientifically rigorous studies consistently find that lowering sodium reduces both blood pressure and cardiovascular disease,” he said on a conference call with reporters. “No other intervention would have as large a benefit for so many people. Even modest reductions in sodium will have substantial benefits.”

FDA Commissioner Robert Califf acknowledged on the same call that some researchers have challenged the notion that lowering sodium is good for cardiovascular health and that there may be legitimate discussions about the benefit of lowering sodium to very low levels.

Still, the preponderance of evidence shows a direct, dose-related benefit to reducing sodium levels, he and other FDA officials said.

The guidelines were issued less than two weeks after the FDA said it planned a major overhaul of the way packaged foods are labeled to reflect the amount of added sugar and specific serving sizes.

The proposed salt guidelines are in theory voluntary. In practice FDA guidance tends to dictate practice. The approach is consistent with that taken by more than three dozen countries that are also working to reduce sodium consumption, Frieden said.

In the United Kingdom, he added, sodium consumption decreased by 15 percent between 2003 and 2011 and was associated with a substantial decline in heart disease and stroke.

The FDA’s recommendations are principally aimed at products marketed on a national scale and national chain restaurants.

The National Restaurant Association said it is offering more menu choices but that “as restaurants continue to develop lower-sodium items, these efforts are challenged by consumer preference, limited technology, and acceptable lower-sodium options that take into account taste, quality and safety.”

It said it is reviewing the draft to assess its next steps.

About half the money spent by Americans on food goes toward food eaten outside the home, according to government figures.