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The soda industry has taken a new approach to the war on obesity. Starting early next year, Coca-Cola (KO) and PepsiCo (PEP) will begin posting calorie counts on select vending machines in Chicago and San Antonio.

The revamped vending machines will be rolled out as part of a competition between government workers in the two cities. (Municipal employees in San Antonio and Chicago are engaged in a "wellness challenge").

Dubbed "Calories Count" by the American Beverage Association, the machines will not only display the number of calories in a can or bottle of soda but also suggest a lower calorie beverage option to consumers. If successful, the retooled vending machines will be expanded nationwide. Health experts say consuming sugary beverages like soda increases obesity in adults and children.

Related: Obesity to Cost Taxpayers 'Billions of Dollars': Weight Watchers CEO

Several cities are weighing a tax on soda purchases and the City of New York will ban sales of sugary beverages larger than 16 ounces in restaurants, stadiums, food carts, movie theaters and fast food joints in 2013.

Related: McDonald's Menu Makeover, NY Soda Ban Don't Go Far Enough: NYT's Mark Bittman

The soda industry's decision to test these new vending machines reveals that beverage makers are trying to change the anti-soda rhetoric, according to Ad Age reporter Natalie Zmuda.

"The beverage industry is being very proactive," she says in an interview with The Daily Ticker. The industry wants to "work hand in hand" with mayors that are considering soda taxes and become "part of the conversation" on obesity.

Posting calorie counts on vending machines could actually boost sales for Coca-Cola and PepsiCo, Zmuda says. Many of the low calorie or zero-calorie beverage brands available to consumers are owned by the two beverage juggernauts. Coca-Cola's product portfolio includes Honest Tea, Odwalla, DASANI, glaceau smartwater and vitaminwater and Minute Maid juices. PepsiCo owns Izze, Tropicana, SoBe Lifewater, Aquafina, Naked Juice, Dole Juices and Ocean Spray.

Coca-Cola and PepsiCo are "actively promoting their low or no calorie beverages potentially at the expense of their full calorie beverages," Zmuda notes.

Soda consumption in the U.S. has been falling since 2005. According to Beverage Digest, an industry trade publication, total sales volume of soda fell 1% in 2011, about the same level as 1996. Americans drank 714 eight-ounce servings of carbonated soft drinks last year compared to 728 in 2010. Soda consumption in 2011 hit the lowest level since 1987.