Earlier this year, the Food and Drug Administration unveiled a revamped Nutrition Facts label for food packages, proposing changes to the iconic white box for the first time since it was adopted 20 years ago.

Among the adjustments: a bolder calorie display, a line for vitamin D and potassium, and updates to the “reference amounts customarily consumed,” upon which serving sizes are based.

Of the changes proposed for the now-trusted label, none has prompted more scrutiny than a new line noting “added sugars” in products.

Nutritionists and some public interest groups have applauded the change, stressing the increasing evidence that links added or artificial sugars to obesity and all manner of metabolic disease. Drawing consumer attention to these added sugars, they say, could result in better choices in the grocery aisle and in better health.

But the food industry knows the little white label is probably the most valuable real estate on a package, and a tiny line for added sugars wields big power — and means potentially big problems for manufacturers.

The industry has, especially in recent years, added more sugars to many products to compensate for lowered fat in a multitude of processed foods. But it has long relied on sugar to woo consumers, something critics say the industry has tried to obscure for decades. Congress, too, has played a role in the sweetener landscape, critics say, by lavishing subsidies on corn and sugar producers, driving up production of both the sugar and high fructose corn syrup that end up in thousands of products.

When the new label was introduced, the industry immediately protested that the “added sugars” line would mislead consumers and has no basis in science.

“We have serious concerns about selective dietary guidance,” Andrew Briscoe, president of the Sugar Association, said at a recent public meeting. “There’s not a preponderance of science, as required by law, to support the added sugars declaration.”

Broader Worries About Sugar

The agency’s decision to include the added sugars line comes amid broader concerns over sugar’s role in disease — and a series of public relations drubbings in recent months.

In June, the Center for Science and Democracy at the Union of Concerned Scientists issued a report accusing makers of high fructose corn syrup and sugar of “tobacco-style” tactics in downplaying the potential health consequences of their products. The report tracks money spent lobbying congressional committees and overall lobbyist spending, including by beverage giants Coca-Cola and PepsiCo Inc. The report notes an uptick in spending in 2010 as Congress weighed and then reauthorized child nutrition programs (PL 111-296). “Sugar interests lobbied heavily on the [Healthy, Hunger-Free Kids Act],” the group wrote “and made political contributions to members of Congress on the committee developing the HHFKA.”

During the subsequent rule-making process, the food industry contributed to the nearly 1,200 public comments, making its position clear. General Mills, maker of Lucky Charms and Cheerios, wrote that “sugar intake has not been shown to be directly associated with obesity or any chronic disease or condition except dental cavities.”

In May, the Environmental Working Group issued an analysis of more than 1,500 breakfast cereals, finding that one-third of their calories come from sugar and that two-thirds of the cereals contained more than a third of the sugar that experts suggest kids should consume in a day. That report came shortly after the release of the documentary “Fed Up,” which blames the food industry for pouring sugar into the foods of an unsuspecting consumer public and causing obesity rates among children to double over the past 30 years.

The scientific evidence on added sugar appears to be mounting, prompting national and global health authorities to suggest limits on sugar intakes.

The Department of Agriculture’s Dietary Guidelines for Americans, last updated in 2010, suggest lowering sugar intakes, but don’t give a specific limit, saying only that combined calories for fats and added sugars should be no more than 5 percent to 15 percent of total daily calories. The Institute of Medicine has not issued a recommended daily allowance for sugar, but suggests that no more than 25 percent of daily calories should come from added sugars.

While health authorities puzzle over these limits, the food and sugar industries are attempting to make their case that added sugars and naturally occurring sugars, like those in fruits or dairy products, are indistinguishable in the body, and therefore shouldn’t be called out on the label.

“There are no analytic techniques to distinguish between artificial and natural,” said Regina Hildwine, a senior policy adviser with the Grocery Manufacturers Association. There’s “no evidence there’s a difference,” she added.

But researchers say the added sugar line is critical because more studies are demonstrating a unique link between added sugar and disease, particularly diabetes.

“This is a science driven proposal,” said Frank Hu, a professor of nutrition and medicine at Harvard’s School of Public Health, in a recent public meeting on the nutrition label. Hu noted that naturally occurring sugars in fruits and dairy are digested more slowly, and said artificial sugars are more strongly linked to fatty liver diseases and insulin resistance. “This phenomenon is unique to added sugars and does not occur with naturally occurring sugars,” he said.

As consumer advocates and the food industry battle it out, both seem to agree on one aspect: Having a line for added sugars on the label would be more meaningful if the FDA establishes a “daily value” or a threshold for sugar intake, which it has not done.

The FDA’s comment period, which has already been extended once, is scheduled to close on Aug. 1, and it’s not clear whether the agency will delay the deadline again.