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There's nothing deceptive about calling a soda "diet," even if it doesn't help you lose weight, a federal appeals court has ruled.

A three-judge panel of the 9th U.S. Circuit Court of Appeals in San Francisco declined to reinstate a class-action lawsuit by a California woman who accused the makers of Diet Dr Pepper of false advertising for using the word "diet" in the product's name.

"Dictionary definitions of the term 'diet' commonly refer to weight loss, or to other health benefits resulting from a special or limited selection of food or drink," the woman, Shana Becerra, asserted in her suit.

She said she had been drinking Diet Dr Pepper for 13 years, believing it would help her lose weight. She felt cheated when it didn't.

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The suit, which also said decades of advertising featuring skinny models enjoying the drink was deceptive, argued that aspartame, the calorie-free sweetener in Diet Dr Pepper, can, in fact, lead to weight gain and other health challenges.

But the court rejected those claims this week, upholding a lower court decision that found that the drink's maker, Dr Pepper/Seven Up Inc., had broken no laws and that the studies Becerra cited about aspartame were insufficient.

In an opinion that came down Monday, Senior Circuit Judge Jay Bybee wrote that the definition of "diet" changes depending on whether the word is used as a noun, a verb or an adjective.

While Becerra had claimed that the word was a noun or a verb meaning "he is dieting" or "she is starting a diet," Bybee said that when it's used as an adjective or a proper noun, the word can mean "reduced in or free from calories."

"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.

He added: "In common usage, consumers know that Diet Dr Pepper is a different product from Dr Pepper —different not only in name, but in packaging and, importantly, taste."

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Becerra and her attorneys didn't immediately respond to requests for comment. Neither did attorneys for Dr Pepper/Seven Up Inc.