When the Food and Drug Administration unveiled its revision of the iconic Nutrition Facts label that appears on processed foods and beverages earlier this year, nutritionists and consumer groups applauded the changes. Even the food industry, which resisted the labels in the first place, greeted the news with a display of muted enthusiasm.

Since then, though, the industry has been reviewing the agency’s proposal, preparing to mount what will likely be a hefty pushback.

With the exception of an added line for trans fats, the label hasn’t undergone any major changes since Congress first approved it under the 1990 Nutrition Labeling and Education Act. Since then, consumers — an estimated 65 percent of adults — have come to rely on the information it provides.

But the agency and nutritionists agree it needs an overhaul, reflecting changes in consumer habits and new nutrition science. The agency has been working on those changes for nearly a decade, publishing an advance notice of proposed rulemaking in 2003.

“After 20 years of this label, we’ve learned a lot and we know we can make improvements,” said Mike Taylor, the FDA’s deputy commissioner for foods and veterinary medicine, in a recent briefing with reporters.

The agency has to walk a fine line, however. “It’s a kind of loved icon,” said Burkey Belser, who designed the current label in the early 1990s, speaking at a recent panel discussion. “So I would suggest to FDA: Mess with it at your peril.”

One of the most notable proposed changes is an increase in the type size of the calories printed on the label, making the total calories much more prominent. That, nutritionists say, could inform consumers who are trying to trim calories and waistlines.

More importantly, perhaps, the agency is also proposing changes to serving sizes to reflect how much consumers actually eat in one sitting — known as the RACC, or reference amount customarily consumed.

For example, a 20-ounce soda will now be considered a single serving, so the calorie count on the label will reflect the entire bottle. Any product that’s less than two times the RACC can now be considered a single serving under the proposed changes.

“They’re saying anything up to 7.9 ounces would be considered a single serving,” said Michael Jacobson, executive director of the Center for Science in the Public Interest. “That’s important. That will stop a lot of deceptive information.”

The beverage industry has said it’s already made the shift. “We welcome many of their proposals, which are consistent with changes already implemented voluntarily by our members,” the American Beverage Association said in a statement. “Since 2010, beverage companies have shown calorie counts on the front of every bottle, can and pack they produce, and have labeled beverages up to 20 ounces as single servings on the [Nutrition Facts Panel].”

But other segments of the food industry aren’t likely to be as comfortable. The dairy foods industry, for example, will have to display calorie counts for a full cup of ice cream under the revised serving amounts, rather than the current half-cup requirement — not something producers necessarily want to highlight.

“We’re carefully looking at the database they used,” said Cary Frye of the International Dairy Foods Association, referring to the data the agency studied in determining the amount of food people typically consume.

Other changes include a lowering of the daily limit of sodium, from 2,400 milligrams to 2,300 milligrams, reflecting the current recommendation in the 2010 Dietary Guidelines. Many consumer groups believe the figure should be lower — 1,500 milligrams — which is the current recommended maximum for people over the age of 50, African-Americans and those with high blood pressure.

Another notable proposed change is an additional line indicating added sugars, thought to boost intake of empty calories. The current Dietary Guidelines call for Americans to consume fewer added sugars. Under the proposal, companies will be required to keep records for two years showing how much sugar they add to products — something the industry will likely fight.

“Despite modern technology there’s no way to distinguish in apple sauce, say, the amount of sugar that comes from the apples and the amount of sugar the producer might add,” said Bruce Silverglade, a principal with OFW Law who worked to get the 1990 law passed. “I think there’s concerns throughout the industry.”

Other proposed changes include removing vitamins A and C from the label, and adding vitamin D, linked to improved bone density, and potassium, linked to prevention of hypertension. Both are considered “nutrients of public health significance.” Food manufacturers will still be able to list A and C voluntarily.

Jacobson said he felt the changes were generally positive. “I think it’s a real improvement over the current labels, and I think the controversy will be over sodium and added sugars.”

The agency, however, declined to set a daily value — or limit — for added sugars. Jacobson and others say that setting a daily limit for overall sugar consumption would provide a more meaningful measure for consumers.

Silverglade asked, “The concern about added sugar is really about calories, and if the basic tenet is to keep it simple, then why include added sugar at all given that they’re not setting a daily value for sugars?”

The agency has said the cost to the industry of updating the labels will run about $2 billion, but the new information could save $20 to $30 billion dollars over two decades from a “wide range” of benefits, largely related to health care.

Silverglade said the benefits aren’t clear. “We know that the changes are going to cost the food industry billions of dollars, that’s for sure,” he said. “But the estimated benefits are more elusive and depend on a myriad of factors.”

While the industry, analysts and consumer groups pore over the proposed rule and offer comments, many say the more important real estate on food packaging is not in the nutrition facts label at all — but on the front of food packages.

“FDA should really be spending more time policing unauthorized front-of-package labeling than tweaking the back,” Silverglade said.

The FDA has sanctioned some industry-led efforts, including one by the Grocery Manufacturers Association and the Food Marketing Institute, dubbed Facts Out Front. “I think the front-of-package disclosure is going to be much more meaningful,” said Jeremy Kees, a professor at Villanova University who specializes in nutrition disclosure on packaging. “More condensed information is better in a shopping environment.”

The FDA has said it would consider mandating front-of-package labeling, but has not done so — and doesn’t appear to be moving in that direction.

“I think the FDA is doing the right thing to see if this can catch on,” Kees said, referring to the Facts Out Front effort, which recently said it would spend $50 million on a media campaign.

In the meantime, as comments from industry and consumer groups flow in before the June 2 deadline, the agency likely will have a big job ahead of it. When the labels were first released in 2003 and 2004, designers offered up at least 35 versions before the current one was accepted. It is now considered one of the most widely reviewed graphics of the 20th century.

“It’s a lot of science on that label. There’s a lot of information you’re asking people to know,” Belser, the designer of the original label, said. “It’ll quickly become a mess with everyone’s personal agenda.”

Clarification of Bruce Silverglade’s comments about added sugar.