The American Beverage Association, whose members include Coca-Cola Co, PepsiCo Inc, and Dr. Pepper Snapple Group Inc, and the Alliance for a Healthier Generation, announced the plan at the Clinton Global Initiative annual meeting in New York. The alliance was founded by the American Heart Association and the Clinton Foundation.

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Soda makers plan to reach their goal by 2025 by educating communities to reduce the calories they are drinking, and offering more zero or low calorie drinks including bottled water.

The American Beverage Association will select an independent evaluator to monitor progress, but it is unclear how many calories a 20 percent reduction would entail.

The measure will likely be based on sales volume, calories per serving and the U.S. census population, said Susan K. Neely, president and chief executive of the American Beverage Association.

"It'd be hard to sustain the progress that has been made so far without this commitment," Neely said in an interview.

Such calorie-cutting initiatives are not new. In 2006 the American Beverage Association and the Alliance for a Healthier Generation partnered to reduce beverage calories in schools.

In 2010, 16 of the biggest U.S. food and beverage companies, including Coca-Cola and PepsiCo, pledged to remove 1 trillion calories from the U.S. marketplace by 2012 and 1.5 trillion by 2015. The companies are part of the CEO-led Healthy Weight Commitment Foundation formed in 2009 to reduce obesity.

In January, companies in the foundation said they had collectively sold 6.4 trillion fewer calories in the United States in 2012 than in 2007. But an analysis by University of North Carolina researchers, published in the American Journal of Preventive Medicine last week, showed that total calories from packaged goods sold to households with children by those companies did not change from 2011 to 2012.
 

Government data show that 34 percent of adults were obese in 2007-2008.