WASHINGTON – Despite some concern in the late 1990s that diet soda might be falling out of favor with Americans, sales over the course of the next decade proved those concerns foolish, as diet soda sales grew by more than 30%, surpassing $8.5 billion in 2009.

Yet, halfway into the next decade, the industry is again concerned, as sales of low calorie soft drinks in the United States have fallen by almost 20% since that peak, according to Euromonitor data cited in the Washington Post in a recent article. The market research firm estimates that diet soda sales are on pace to drop another 5% this year, and another 25% from the 2009 peak by 2019.

The diet soda slowdown isn't exclusive to the U.S., either. While regular Coca-Cola and Pepsi are still growing globally, their diet versions are not. According to the Post, low-calorie sodas are experiencing fallout from two trends among American consumers: a decline in overall soda consumption and, according to the Post, “a perhaps more significant trend, is a growing mistrust of artificial sweeteners.”

Euromonitor analysts confirmed that their findings show that consumer attitudes toward sweeteners have changed significantly, evolving to a noticeably negative perception of artificial sweeteners. Perhaps in an effort to stem the tide, Coke and Pepsi have both recently introduced mid-calorie Stevia-sweetened sodas: Coke Life and Pepsi True.