THE shoppers looked skeptical.
"This is the first drink that can actually help you lose weight," sales representative Anthony Monforte said confidently, handing out tiny samples of a new soft drink, Celsius, at a Vitamin Shoppe in Aliso Viejo.
Leslie Bedford and Marsha McDonogh, office workers who had stopped by on their lunch break, took cautious sips. "Hmmm. It does taste like RC Cola," McDonogh said, agreeing with Monforte's description. Sold on the taste -- and especially the promise -- she plunked down $6.99 for a four-pack.
"If it really works, that's great," Bedford said. "Everyone in our office wants to lose weight one way or another."
Beverage makers are counting on it. Stung by falling sales and criticism that sugar-sweetened soft drinks raise the risk of obesity, they're reaching into scientists' laboratories to come up with healthier products -- vitamin waters, sports drinks, fortified juices and now so-called negative-calorie drinks. The drinks, most notably Celsius and Coca-Cola's and Nestle's Enviga, promise to boost metabolism and burn calories.
The key ingredients are green tea and caffeine. Celsius' manufacturer says its particular combination will increase metabolism enough to burn up to 77 calories per 12-ounce bottle; Coke states that three 12-ounce cans of Enviga will burn 60 to 100 calories. Snapple has also introduced green tea beverages, with labels that claim they boost metabolism.
"Consumers are looking for some functional benefit," says John Sicher, editor and publisher of Beverage Digest, an industry trade publication. "They are saying they want their calories to do something for them."
The effects of the green tea drinks go beyond those of caffeine-laden zero-calorie sodas, the manufacturers of Celsius and Enviga say. An antioxidant found in green tea -- epigallocatechin gallate, or EGCG -- significantly increases metabolism, they say. This, in turn, boosts the body's ability to burn fat.
Raising metabolism is more complicated than simply ingesting a chemical that speeds up the heart rate, which often makes users jittery. Though scientists still aren't sure just how EGCG works, some suggest it triggers greater production of a neurotransmitter called norepinephrine, elevating metabolism. Caffeine also raises the metabolic rate, and early research suggests combining EGCG with caffeine is the key to a measurable increase.
The concept is intriguing -- but far from proven, pharmacology experts point out.
"The data are still emerging," says Roger Clemens, a spokesman for the Institute of Food Technologists and an adjunct professor of pharmacy at USC. "They are not convincing."
Jeffrey Blumberg, a senior scientist in pharmacology at Tufts University is similarly skeptical. "In really carefully controlled studies, you can actually find an increase in metabolic rate," he says. "But if the effects are modest, it might be hard to see them in the real world."
Other studies have shown that the antioxidant does have potential to help prevent some types of cancer, they acknowledge, but the effects on metabolism shouldn't be counted on at this point.
Put to the test
The makers of both Enviga and Celsius say they have research to support their weight-loss claims.
In a study of Celsius, which contains five to 10 calories a bottle depending on the flavor, 20 people were divided into two groups with one group consuming 12 ounces of Celsius and the other group consuming 12 ounces of Diet Coke. The volunteers' metabolic rate was measured before and after consumption. The study showed an average increase of 12% in metabolic rate over a three-hour period among those drinking Celsius compared with a 4% to 6% rise in the Diet Coke drinkers.
Depending on the person's own metabolism (which varies by fitness level, weight, gender and age among other factors), a 12% increase could result in burning up to 77 calories a bottle, says Elite FX, the manufacturer of Celsius, which funded the study. The research was conducted at Ohio Research Group of Exercise Science and Sports Nutrition and was presented last year at a meeting of the International Society of Sports Nutrition.
A study of Enviga, which contains five calories per can, showed that drinking three 12-ounce cans a day increased calories burned by 60 to 100 per day. The study, performed at the University of Lausanne, has not been published.
"The data show the green tea extract appears to enable this gentle boost in the metabolic rate," says Rhona Applebaum, chief scientist of Coca-Cola. "The second mechanism is caffeine. The two together -- what we have found and what other studies have found -- produces this synergy that allows for this gentle boost in rate."
Enviga was launched in October in the northeast United States and will become available nationwide in January. Sweetened with aspartame, it comes in three flavors -- green tea, berry and peach -- and sells for about $1.29 to $1.49 a can.
Celsius, which sells for roughly $1.99 a bottle at Vitamin Shoppe stores and Albertsons, was launched in June 2005. Sweetened with sucralose, or Splenda, it too is available in a variety of flavors.
Caffeine, of course, plays a role in the drinks' effect on metabolism. Celsius contains 200 milligrams of caffeine and Enviga 100. A Coke or Pepsi contain approximately 35 milligrams of caffeine; a 5-ounce cup of coffee has about 100 milligrams. Celsius also contains seeds of guarana, an Amazonian berry, which contain caffeine.
But EGCG's effect on metabolism is stronger than that of caffeine, the drink companies say.
"We tested the whole bottle," says Janice Haley, owner and vice president of Elite FX. "We know it's all the ingredients working together that causes the increase in metabolism."
The same EGCG-and-caffeine combination can presumably raise metabolism and burn calories among drinkers of hot green tea. Numerous laboratory and animal research, plus a few studies in humans, have measured an increase in metabolism from green tea consumption. And many dietary supplements containing green tea extract also make weight-loss claims.
But the green tea carbonated soft drinks are aimed at specific markets: gymgoers watching their weight, and consumers who normally down several 150-calorie sugary sodas a day but are thinking of switching to something healthier.
Of course, simply exercising and replacing regular sodas with low- or no-calorie drinks could obviously help Americans shed excess pounds. And, as nutritionists point out, it's pretty easy to cut 100 calories a day in other ways, such as by skipping one cookie or not adding a tablespoon of butter to pasta or bread.
But for people who simply want to feel that they're helping the cause, not actually hurting it, the drinks could fill a niche.
"It's all about watching calories," Haley says.
That message is one consumers know well.
Spurning soft drinks
Shoppers appear to be tuning in to the chorus of health professionals who say soft drinks are playing a sizable role in rising rates of obesity. Sales of carbonated soft drinks fell last year -- by 0.7% -- for the first time in two decades.
A study presented last year at the Experimental Biology annual meeting found that sugary soft drinks are the leading source of calories in the average American diet, accounting for as much as 9% of energy consumed. (A little more than a decade ago, white bread was the biggest source of calories.) The study also found that obesity rates were highest among regular soft-drink consumers.
A review of 30 studies published in August in the American Journal of Clinical Nutrition found that greater intake of sugar-sweetened beverages was linked with weight gain and obesity in both children and adults.
Today, sweetened soft drinks are targeted for removal from campuses by school boards and are vilified by most health professionals. A few health organizations have even proposed adding a federal tax to soft drinks to try and curb consumption.
"We're at a turning point," USC's Clemens says. "Consumers are really being encouraged to make more healthful choices."
These new drinks fit that bill -- for some people.
Although Celsius' maker has backed away from earlier statements that drinking it regularly over the course of a year could lead to a 17-pound weight loss, the company markets Celsius as a "replacement" for high-calorie, sweetened soft drinks.
"We are careful not to say that this is a weight-loss product," Haley says. "We don't want people to think this is Jenny Craig or Slim-Fast. It's a great-tasting drink that is a great alternative to soft drinks or coffee drinks or even diet sodas."
Coke views Enviga as "another step" for consumers who are trying to become healthier, Coca-Cola's Applebaum says.
"I can't emphasize enough that this is not a magic stick," she says. "If you are going to eat everything in sight, this product isn't for you. It won't overcome bad behaviors. But if you are making progress, this is an additional step."
Enviga doesn't cause adverse effects such as increased heart rate, blood pressure or respiration, notes Applebaum. Previous diet drinks and teas that contained high levels of caffeine or the herb ephedra have caused serious health problems such as heart attacks in some people.
Celsius is also safe, Haley says. But consumers who are caffeine-sensitive should avoid the product, she says.
Tuft's Blumberg, a member of the scientific advisory board to the trade group Tea Council of the USA, agrees with the notion that the so-called calorie-burning drinks can play a role in a diet-and-exercise program.
"If you're doing lots of good things, that contribution of 60 to 100 extra calories is a help," he says. "The problem is that people tend not to look at these things in a sensible manner. You can lose 60 calories a day by taking this product three times a day. But if you are consuming 3,000 calories a day, 60 calories is not a meaningful amount."