According to the Code of Federal Regulations, a soft drink can be labeled "diet" as long as that label is not deemed "false or misleading." The terminology, long used by soda companies to designate sugar-free and low-calorie varieties, has been around and widely used for decades.
The terminology has survived other recent challenges. In 2015, a petition from consumer group U.S. Right to Know made a similar request of the federal government: that the "diet" label on soda be ruled misleading. The Federal Trade Commission denied the petition. The FDA never acted on it.
But acceptance of the term doesn't mean that it's still relevant. These lawsuits may change the way that soft drinks and other products are labeled. Today's consumers don't diet like they did a generation ago, and the label "diet" means something different to everyone. Outside of beverages, the generic "diet" label isn't on many products anymore.
Instead of following the generic low-sugar, low-fat diet of yesteryear, consumers watching what they eat now may prefer products with more well-rounded health halos, things that are less processed, or items that help them follow specialized diets such as paleo and keto. Regardless of how the court rules, manufacturers may take a look at the label claim and realize it is not specific enough to describe what a consumer is getting from a sugar-free, low-calorie soda.
Manufacturers may want to ditch the "diet" name anyway. While soda's overall market share has been falling over the last several years, diet soda's share has plunged much more quickly. Diet beverages have fallen out of favor with consumers, possibly because of their artificial sweeteners, or because of studies linking diet soda consumption with health and weight issues. But with few conversations about diet soda on social media, the drinks will only continue to lose their market.