Will Diet Coke Be the Same … With Vitamins?

For most of the last century vice was defined by critic Alexander Woollcott's remark that everything he liked was "illegal, immoral or fattening." That, though, was before the invention of Diet Coke. "It's my one vice," says Amy Stensrud, a 46-year-old Seattle mother of two, who buys a 32-ounce container of Diet Coke at a 7-Eleven every morning, right after the gym. She has in effect defined vice upward as something "inconsistent with my values," which was never Woollcott's problem with bathtub gin.

But now her only sin is in danger of being transformed into a virtue, as Coke rolls out a new version of Diet Coke with added vitamins and minerals. Blue-capped bottles of Diet Coke Plus will begin showing up in stores this week, empty of calories but containing 10 to 15 percent of the daily requirement of niacin, zinc, magnesium and vitamins B6 and B12. It isn't meant to replace Diet Coke, now the third best-selling soft drink in America, after Coke Classic and Pepsi; it's just a part of Coke's plan to conquer the world by making so many kinds of soda that stores won't have room for anything else. Competition is especially fierce now in the $70 billion soft-drink market. For the first time in recent history, the amount of soda sold in the United States—more than 16 billion gallons—fell in 2005, and again in 2006. Diet Coke Plus, says John Sicher, publisher of Beverage Digest, stands at the convergence of two powerful trends: the rise of diet drinks (30 percent of the soda market, up from 25 percent in 2000) and the move toward "functional" products such as sports drinks. According to Coke spokesman Scott Williamson, Diet Coke Plus will be advertised with slogans that merely imply it's good for you ("Your best friend just got friendlier!") without making any health claims. To do otherwise, he said, "would reinforce the false notion that soft drinks are unhealthy to begin with."

Diet Coke Plus grew out of what Williamson calls Coke's "ongoing dialogue" with its customers. The same process gave rise to the dozen or so permutations of Coke on the market, including Diet Coke in 1982, followed by Diet Cherry Coke and Diet Coke Cherry (the same thing), and Coca-Cola Zero, a no-cal drink for men who are put off by the feminine connotations of "diet." Diet Coke Plus tastes something like Diet Coke, but sweeter, because it contains both aspartame and a sweetener called acesulfame potassium. Its choice of added nutrients seems somewhat arbitrary and doesn't include the one substance that might arguably be useful, calcium. "What's the point of adding vitamins to a soft drink?" wonders nutritionist Marion Nestle of NYU. "You can take a multivitamin pill. You can even take it with a Diet Coke."

You might need to, if you're a Diet Coke fanatic like Victoria Beckham, the former Posh Spice, who drinks almost nothing else and claims to hate the taste of water. Diet Coke is the one addiction that public figures willingly own up to. It's the only beverage in the back of producer Harvey Weinstein's limo, and makes up one half the diet of Florida State football coach Bobby Bowden. The other half consists of peanuts. A 12-ounce can of Diet Coke, which may contain from a third to half the amount of caffeine in eight ounces of coffee, is the breakfast drink of choice for many college students. "I like that fake sugar taste," says Stanford sophomore Margot Markman, who usually has the first of four daily 16-ounce cups from her sorority's fountain at 8:15. It is one of the few things you can buy at a gas station that's also an object of connoisseurship. Kristen Scaletta, a senior at Northwestern University in Evanston, Ill., who recently cut back from about a gallon of Diet Coke a day to three quarts, drinks it only from cans, preferably at room temperature—a taste she formed as a child when she had to sneak it past her parents to drink in her bedroom. Other people insist on the flavor of Diet Coke from liter bottles, or McDonald's.

Taste aside, what makes Diet Coke so addictive? Caffeine produces physical dependence, as anyone who has suffered through the headaches of coffee withdrawal can testify. But addiction specialists pooh-pooh the idea that people can be "addicted" to soda, in the sense that it interferes with normal life. The other obvious point about it is that it has no calories. Not everyone who drinks it is trying to lose weight, but presumably none of them cares to subject her body to the 1,120 calories in eight cans a day of regular Coke. The role of diet sodas in weight loss is a contentious area of research. "Studies suggest that diet drinks can bump calories out of the diet short term," says Dr. David Katz, a public-health specialist at Yale, "but that people compensate over time by eating more sugar." An unpublished seven-year study by Sharon Fowler of the University of Texas found that the more diet sodas people drank, the more likely they were to be overweight—although that doesn't prove cause and effect. Fitness guru Richard Simmons estimates that 85 percent of the people who come to him to lose weight drink diet soda habitually.

People do worry about the health effects of diet soft drinks. There is some research to suggest that all colas, not diet ones in particular, may contribute to bone loss in women, but all the evidence isn't in yet. A new study found that the acid in sodas erodes tooth enamel (although full-sugar versions, and citrus flavors, are worse). As for artificial sweeteners, a study of the literature by Valerie Duffy of the University of Connecticut suggests they're safe. "They've all been through extensive testing," she says, "for acute toxicity, chronic toxicity, carcinogenic potential, effects on fertility, lactation, fetal development" and about six other things. To reach the FDA's "acceptable daily intake" of aspartame—which itself has a wide margin of safety—"you'd have to drink 18 cans of Diet Coke every day of your life," says Hud Englehart, a spokesman for aspartame's manufacturer, NutraSweet. (The actual figure, Duffy points out, varies with the person's weight.) "It's pretty hard to drink that much."

Mr. Englehart, meet Rich Underkofler, a 47-year-old from Euclid, Ohio. "I drink this stuff like crazy," Underkofler says. "I don't even go to restaurants that don't serve Diet Coke." Checking his refrigerator one night last week, he found two 12-packs. That would last him, he figured, a little more than a day.