The Wall Street Journal reports that sales of low-cal carbonated drinks falling faster than other types. Coca-Cola Co. and rivals had hoped zero-calorie recipes would lift the $75 billion U.S. soda industry after Americans began scaling back on full-calorie soda in the late 1990s amid obesity concerns. For a while they helped: Diet soda’s share of consumption rose from 26% to 31% between 1990 and 2010. Now diet soda is the industry’s weightiest problem. Store sales of zero- and low-calorie soda plunged 6.8% in dollar terms in the 52 weeks through Nov. 23, while sales of regular sodas dropped 2.2%. As a category, diet soda has contracted more than regular soda for three straight years.