By Jonathan Davies
Pepsi is now the second most popular fizzy drink in the US after outselling Diet Coke last year.
Figures from the Beverage Digest magazine showed Coca-Cola maintaining top spot, with Diet Coke sales falling 6.6%. Diet Pespi fell by more than 5%.
Both Coca-Cola and Pepsi increased sales overall, with Coca-Cola posted its first overall sales increase since 2000.
Beverage Digest suggested that the sugarless alternatives like Diet Pepsi, Diet Coke, Pepsi Max and Coke Zero has lost popularity due to concerns over the side effects of artificial sweeteners used in place of sugar.
In a growing sign of the more health-focused diet, bottled water pushed Nestle sales up 9%.
"There has been a tremendous migration to other categories in recent years," John Sicher, editor of Beverage Digest, told the BBC.
He said that the likes of Coke and Pepsi are trying to lower the calories in their drinks with artificial sweeteners.