What highly nutritious food is defending itself to American consumers -- even though they've consumed it happily for decades?

What drink is full of potassium, folic acid, vitamin C and a slew of antioxidants?

What longtime American favorite has slipped enough in sales that its industry is now mounting a major advertising campaign?

The answer to all these questions is orange juice.

Shunned by the low-carb diets for its concentrated carbohydrates and pummeled by a drop in sales, orange juice is having to polish up its image for the American public. Instead of being hailed for its many health benefits, orange juice has become an easy carbohydrate to forgo. And the orange juice industry is worried.

Orange juice consumption is at an all-time low, according to Florida Citrus Mutual, a trade association of 11,000 citrus growers. In the past two years, orange juice consumption has dropped about 5 percent. Last year, Americans drank about 4.7 gallons of orange juice. In 1997, the figure was 5.8 gallons. Since 1999, overall orange juice consumption has dropped 10.8 percent.

In the past year -- the time that corresponds to the growing popularity of the South Beach Diet -- that drop has been particularly noticeable. In the 52 weeks preceding April 18 alone, chilled orange juice sales fell 4.1 percent by volume, according to Information Resources Inc., a Chicago-based market research firm.

"The low-carb diet is the single biggest factor in the decrease in orange juice sales," says Dan Gunter, executive director for the Florida Department of Citrus.

"Slightly under 80 percent of American households right now buy orange juice," says Gunter. "Two years ago, it was about 81 percent." Gunter added the drop was particularly noticeable in the "heavy user" category -- households that consume 12.5 gallons or more annually.

In December 2003, the Florida citrus department asked the A.C. Nielsen Co. to investigate the sales drop and look at the connection between low-carb attitudes and orange juice. The findings: Over the past year, of the 2,600 households randomly surveyed, 26 percent of people knowingly reduced their orange juice consumption. And of that 26 percent, 35 percent did so because of low-carb dieting.

Getting specific numbers from the major orange juice players is a challenge. "We don't have a complete picture, says Charles Torrey, Minute Maid's marketing director for refrigerated products. "From what we can survey, about 10 percent of consumers are drinking less orange juice, stating calories, sugar or carbohydrates as the reason. We also can surmise through secondary data, such as articles in nutrition journals and newspapers, [that] about 4 percent of consumers may be avoiding orange juice specifically because of the low-carb diet." At Tropicana, chief marketing officer Ron Coughlin admits the orange juice category has seen a decline but says orange juice sales at Tropicana are steady.

Orange juice has been a pervasive presence at the American table, offered at breakfast counters in the same breath as coffee. But it wasn't always that way. It didn't enter the U.S. market until the 1920s when citrus growers in Florida and California joined forces in a major ad campaign to promote oranges and orange juice. The concept of vitamins had recently been introduced to the public, and orange juice -- lauded for its vitamin C in the battle against scurvy -- became an essential part of the American breakfast. "Rarely has a food habit been adopted so quickly by so many people," says Andy Smith, editor of the forthcoming Encyclopedia of Food and Drink in America (Oxford University Press). "Americans became convinced during this time that [their] health depended on orange juice each morning."

At first that juice was fresh. "The vast abundance and the lowering of cost of oranges during the early 20th century made fresh-squeezed orange juice common at breakfast," says Smith. Then during the 1920s and '30s, the focus shifted to canned juice.

But the newly refined freezing process and advances in transportation developed during World War II propelled orange juice into refrigerated trucks, supermarkets and kitchens after the war. Industry giants Tropicana and Minute Maid point to their role in that process.

Minute Maid gets the credit for frozen concentrate. Before the end of the war, Minute Maid's eventual founder Jack Fox was working on powdered juice for the U.S. Army.With the end of the war, he came upon freezing, an interim process that had more promise. In 1949, his company, the Florida Foods Corp., changed its name to Minute Maid. Tropicana gets the credit for flash-pasteurizing fresh orange juice (by raising the temperature of the juice for a very short time) in 1954 and shipping it in wax cartons.

The industry has always had its challenges: freezing weather that cut into crops; diseases that attack citrus groves. The familiar 64-ounce containers also face competition from other juice drinks on supermarket shelves (often marketed in individual serving sizes), and from an on-the-go lifestyle.

Then came the sales drop of the past three years. "No one was quite sure why," says Gunter. "We started looking for the other things and only recently discovered what it really was -- the low-carb diet and an increased awareness even among people not on the diet that orange juice has carbs in it."

(A typical eight-ounce glass of orange juice has 26 to 27 grams of carbohydrates. That's far more than an eight-ounce glass of tomato juice at 10 grams, whole milk at 11 grams or skim milk at 12 grams, according to "The Nutrition Bible" by Jean Anderson and Barbara Deskins (Dimensions, 1997).

The Florida Department of Citrus decided to address the problem by emphasizing the health values of orange juice.

"We'd gotten away from plugging vitamin C and potassium and folic acid," says the department's spokesman Andrew Meadows. "And lately there's been a lot of buzz around antioxidants, and orange juice is loaded with them. The underlying message is that if you're on a diet or not, orange juice is such a valuable source of vitamins and minerals, that you don't need to cut it out."

Last month, the citrus department turned to television as part of a $1.8 million campaign to revitalize orange juice sales. Its catchy ad features an upbeat guy throwing things into a blender to make an ideal but very unattractive health drink: rutabagas for vitamin C, liver for thiamin, Brussels sprouts for vitamin B6, a little fish for magnesium. Or, he says, you could just drink a glass of Florida orange juice.

The point, after all, is sales. And, according to Florida Citrus Mutual, this year's drop in sales is happening when there is a record orange crop on the Florida trees and a record high amount of already-squeezed juice in storage.

Historically, the orange juice industry has developed products designed to attract new consumers or to raise the level of American orange juice consumption. This is one of those times. "It's an uphill battle," says Gunter. "There are lots of competing products on the market. Consumers are bombarded with marketing messages every day. Only 16 percent of American users drink orange juice every day. Lots of consumers drink it three days a week or often. But we know there's room for expanding our sales."

At times, those products have been designed to meet a lifestyle preference; at other times, to meet an actual or perceived nutritional need. There are juices available, for example, that appeal to parents' concerns for their children's health, to consumers worried about heart disease and to those who are trying to bolster their immune system or are sensitive to a high-acid diet. "When we can, we take the opportunity to do innovations to create a niche that will drive sales," says Minute Maid's Torrey.

Currently, the industry is developing and pushing products that appeal to the low-carb crowd. Last month, Minute Maid, which is owned by Coca-Cola, brought out Minute Maid Premium Light, with half the carbs, calories and sugar of regular orange juice. Next week, Tropicana, which is owned by PepsiCo, will bring out a revised version of its new Tropicana Lite'n Healthy, with half the carbs, calories and sugar of regular juice. (In January, the product was introduced with one-third the sugar, calories and carbs, but then was reconfigured, making it competitive with Minute Maid's Premium Light.) "It's a complete match [with Tropicana Pure Premium orange juice] from a nutritional standpoint," says Coughlin.

The industry is naturally hoping that the low-carb way of life is a trend rather than a revolution. "We think it will run its course," says Minute Maid's Torrey. "I believe people will go back to what makes sense -- a balanced diet governed by reason and discipline."

Many other people who don't make their living selling orange juice are urging consumers to adopt a balanced attitude as well.

"When you look at foods through a low-carb lens, you miss the big picture," says Ed Blonz, an author with a PhD in nutrition. "If you want to lower the risk of chronic diseases -- obesity, diabetes or coronary heart disease -- it makes little sense to reject wholesome, nutrient-dense foods such as orange juice in favor of a low-carb, fast-food entree or some carb-free processed food. Orange juice has vitamin C, folic acid, potassium and untold naturally occurring beneficial compounds. All this make it a great food."