Beer purists scratch their heads and wonder how "low carb" beers got to have such a huge share of the market. After all, you might think that if you are supposed to shun carbohydrates as part of your diet, you probably would just stay away from beer altogether. But low carb beer is big business, with Anheuser-Busch's Michelob Ultra claiming 2.9 percent of the US market. Coors Brewing got into the game late with their Aspen Edge, and has been trying to make up for lost time with an aggressive ad campaign that claims people prefer the taste of Aspen Edge to Michelob Ultra. Coors may have to go to plan B, though. Anheuser-Busch has announced that due to its "alerts" to Coors that the Aspen Edge ad campaign is unfairly misleading, Coors is pulling those ads. We'll see whether Coors comes up with a new version of the same comparison commercials or tries to build up Aspen Edge sales in another way.