Starbucks is facing a lawsuit over its "sugar-free" protein drinks, with consumers alleging some contain nearly as much sugar as a candy bar.The proposed class-action lawsuit, filed Oct. 2 in federal court in Washington state, targets eight hot and iced Starbucks protein beverages, including its Sugar-Free Vanilla Protein Latte, Sugar-Free Caramel Protein Latte and protein matcha drinks.The beverages contain between 13 and 21 grams of sugar in a venti-sized serving, according to the lawsuit, which reportedly argues that "no reasonable consumer" would expect a drink called "sugar-free" to contain that amount.POPULAR PANTRY PRODUCT CAN'T LEGALLY BE CALLED PEANUT BUTTER — HERE'S WHYThe suit was brought by three consumers who bought the drinks in California, New York and Washington. It asks the court to stop Starbucks from using "sugar-free" to describe products that contain sugar.Starbucks is disputing the allegations."We believe these claims have no merit," a Starbucks spokesperson told Fox News Digital.GROCERY SHOPPERS MAY BE RELYING ON A 'MISLEADING' CLUE WHEN CHOOSING HEALTHY FOODS"Starbucks has consistently and clearly provided information about its protein beverages, sugar-free options, customization choices, and nutritional content across product announcements, menus, marketing materials, Starbucks.com and the Starbucks app, and we intend to vigorously defend ourselves in this matter."The company says the sugar in the drinks comes naturally from protein-boosted milk rather than added sugar, and that sugar-free syrups are used for flavoring.Nicolette Pace, a New York-based registered dietitian and certified diabetes educator, noted that lactose in milk is a naturally occurring sugar and is not counted as an added sugar, but "sugar-free" and "no added sugar" are not the same.DIRTY SODA DRINKS ARE EVERYWHERE, BUT DOCTORS WARN OF HEALTH RISKS: 'METABOLIC DISASTER'"Sugar-free" does not necessarily mean a product contains zero sugar, added Dr. Michael Aziz, an internist at Lenox Hill Hospital in New York City. Under FDA regulations, products labeled "sugar-free" generally must contain less than 0.5 gram of sugar per serving."No added sugar," meanwhile, means sugars or sugar-containing ingredients have not been added during processing or preparation, though a product can still contain naturally occurring sugar, as Starbucks says its protein drinks do. Naturally occurring sugars can still affect blood glucose levels, making the total carbohydrate content important for people with diabetes to consider.JUST ONE SMALL SERVING OF ULTRA-PROCESSED FOOD A DAY LINKED TO HIGHER DISEASE RISK, MAJOR STUDY FINDSThe plaintiffs argue that they paid more for products advertised as sugar-free than they would have for comparable alternatives, said Danny Karon, an Ohio-based class-action attorney who is not involved in the case. "The challenge will be convincing the court — and then the jury — that consumers relied on Starbucks' alleged misrepresentations when making their purchases," Karon told Fox News Digital.CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTERBeyond the protein beverages cited in the lawsuit, Aziz and Pace warned that other Starbucks specialty drinks can pack significant amounts of sugar, underscoring the importance of considering nutrition information, serving size and add-ons such as whipped cream and drizzles.A venti Java Chip Frappuccino can contain nearly 80 grams of sugar, or roughly 20 teaspoons, they said. They also pointed to the Caramel Ribbon Crunch Frappuccino and seasonal drinks such as the Peppermint Mocha and Pumpkin Spice Latte, which, depending on size and customization, can have almost as much sugar.CLICK HERE FOR MORE LIFESTYLE NEWS"That's massive amounts of sugar when we know that a soda has 63 grams of sugar," Aziz said, referring to standard 20-ounce bottles of popular regular sodas."Size does matter when it comes to these things at Starbucks," Pace said. The American Heart Association recommends limiting added sugar to about 6 teaspoons, or 25 grams, per day for most women and 9 teaspoons, or 36 grams, for men, she noted.CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTERShe stressed, however, that those recommendations apply to added sugar, not naturally occurring lactose in milk.For consumers looking to reduce their intake, she suggested keeping the order simple, and choosing a smaller size.Aziz recommends, "If you want to have a treat, maybe just have a simple latte or a cappuccino."