WASHINGTON (AFP) ― Faced with falling sales of its diet soda, Coca-Cola is running ads in the United States that say its sugar-free beverages, sweetened with the chemical aspartame, are safe.

The print ads which began appearing Wednesday in major U.S. newspapers show a pair of laughing women, one holding a bottle of diet Coke in hand, alongside text that reads: “Quality products you can always feel good about.”

The copy beneath the picture says, “The safety of aspartame is supported by more than 200 studies over the last 40 years.”

The soda industry is facing declining U.S. sales as some blame sugary drinks for fueling the obesity epidemic in America.

Diet Coke sales fell three percent in 2012 compared to a year earlier, and Coke was down one percent, according to Beverage Digest. Meanwhile, Pepsi slid 3.4 percent and Diet Pepsi fell 6.2 percent.

Scientists are not in agreement on whether aspartame, approved in the 1980s, is safe over the long-term, said Karen Congro, a nutritionist and director of the Wellness for Life Program at the Brooklyn Hospital Center.

“Despite claims from Coke and other companies about the safety of aspartame, we still don’t know about its long-term effects,” she said in an email to AFP.

“There is a growing backlash against ― not only diet soda ― products with artificial sweeteners and other artificial ingredients.”

Congro said recent research shows that people who consume artificial sweeteners so as to stick to a diet can actually end up craving more calories.

“Relying on artificial sweeteners probably causes cravings for sweets and sugar, which can contribute to obesity and poor eating habits,” she said.

“It’s possible that the brain reacts to artificial sweeteners in diet soda and other products by sending out insulin, which can make people hungry ― especially for sugar.

The U.S. Food and Drug Administration says aspartame “may be safely used in food in accordance with good manufacturing practice as a sweetening agent and a flavor enhancer in foods.”