"Sparkling beverage volume fell 2 percent, largely due to softer Diet Coke volume," said CEO Muhtar Kent, adding that Coca-Cola was moving to address headwinds and misconceptions.
(Read more: Coke matches earnings estimates)
The effort will involve "increase[d] aggressive sweetener innovation, transparent consumer communications, continued packaging evolution and new partnerships with credible third parties around the world who will use meaningful facts to defend and protect the sparkling category," Kent said.
The overall carbonated cola category has also seen pressure in recent years, according to data from Euromonitor. Volume dropped 3.6 percent in the U.S. last year versus 2012. Worldwide, volume growth was flat.
—By CNBC's Katie Little. Follow her on Twitter