Diet Dr Pepper cans display for sale in the supermarket. Photo: Zety Akhzar/Shutterstock

That New Year's resolution to lose weight might not include Diet Dr Pepper—at least, according to a federal appeals court that affirmed dismissal of a case challenging the soda's health claims.

In an opinion Monday, the U.S. Court of Appeals for the Ninth Circuit concluded that the word "diet" in Diet Dr Pepper did not mislead consumers into believing they could lose weight.

"Diet soft drinks are common in the marketplace and the prevalent understanding of the term in that context is that the 'diet' version of a soft drink has fewer calories than its 'regular' counterpart," wrote Judge Jay Bybee of the U.S. Court of Appeals for the Ninth Circuit. "Just because some consumers may unreasonably interpret the term differently does not render the use of 'diet' in a soda's brand name false or deceptive."

San Diego plaintiffs attorney Jack Fitzgerald, of The Law Office of Jack Fitzgerald, did not return a call for comment.

Baker Botts partners Evan Young, in Austin, Texas, Van Beckwith in Dallas, and Jonathan Patchen in San Francisco, represented Dr Pepper/Seven Up Inc. The Texas-based company did not respond to a request for comment.

The ruling is the latest in a class action challenging the health claims of diet soda. Fitzgerald brought cases in California and New York, where the U.S. Court of Appeals for the Second Circuit found this year that that "diet," in the context of Diet Coke, did not mean weight loss but, instead, fewer calories. In previous summary orders, the Second Circuit upheld dismissal of two other New York cases this year involving Diet Dr Pepper and Diet Pepsi.

On Dec. 23, the Ninth Circuit also dismissed the appeal of another Fitzgerald case challenging Diet Coke, concluding it lacked jurisdiction because the judge's order "shows no intent to dispose of the entire action."

In the Diet Dr Pepper case, Fitzgerald's client, Shana Becerra, had argued that the drink deceives consumers into believing they can lose weight, or at least not gain weight, when drinking the soda.

The Ninth Circuit, in its order, focused on Dr Pepper's argument that the plaintiff defined the word "diet" as a noun or verb, not as an adjective, as used in its product's name.

"When considering the term in its proper context, no reasonable consumer would assume that Diet Dr Pepper's use of the term 'diet' promises weight loss or management," Bybee wrote. "In context, the use of 'diet' in a soft drink's brand name is understood as a relative claim about the calorie content of that soft drink compared to the same brand's 'regular' (full-caloric) option."

The panel also dismissed allegations that Diet Dr Pepper's advertising alluded to weight loss with "the use of attractive, fit models."