Drinks giants Coca-Cola and Nestlé have this week been officially slapped with a lawsuit for claiming their new Enviga energy drink can help consumers burn off calories.
The firms were notified of intent to sue in December by consumer group Center for Science in the Public Interest (CSPI), which asked for the claim to be removed from the product labels.
But according to Beverage Partners Worldwide, a Coca-Cola and Nestlé partnership that has developed Enviga, "CSPI has their sound bites, we have sound science".
"We will vigorously dispute CSPI's unsupported allegations and will energetically oppose this meritless lawsuit."
The filing of the lawsuit promises another public relations battle between soft drinks firms and campaign groups. Enviga, launched in the US last month, is a carbonated, green tea beverage that claims to burn more calories than it provides.
According to chief Coca-Cola scientist Rhona Applebaum, it is the optimum combination of Enviga's green tea, caffeine and plant micronutrient content, which creates the 'negative calorie effect'.
The formula was made possible through access to decades of research on green tea by the Nestlé Research Center in Switzerland. It found the tea contained a powerful antioxidant, EGCG (epigallocatechin gallate), which could speed up metabolism and energy use when combined with caffeine.
Tests have shown that drinking three cans of Enviga everyday could burn an extra 60-100 calories in thin to normal weight people, the firms announced.
But CSPI accused both companies of misleading advertising, alleging that evidence for Enviga's 'negative calorie' effect was not substantial.
It also criticised the drink's caffeine content, around 300mg in one can, which sits right at the top end of the maximum daily intake advised by the American Dietetic Association.
Some scientists in the US recently called for all caffeinated drinks to show caffeine content on their labels, even carbonated sodas. Current caffeine levels in drinks were not clear enough for consumers, said their article, published in the Journal of Analytical Toxicology.
"In certain people, consumption of caffeine causes serious health effects, such as anxiety, palpitations, irritability, difficulty sleeping and stomach complaints," said Dr Bruce Goldberger, one of the researchers.
In December, the US Food & Drug Administration (FDA) held a hearing on how to regulate labeling and health claims for functional foods and beverages, such as Enviga, which have no legal category of their own to date.
Today's lawsuit was filed in US District Court in New Jersey.