Several of the nation's largest food companies say they will take 1.5 trillion calories out of their products by 2015 in an effort to reduce childhood obesity.

First lady Michelle Obama announced the move Monday after a coalition of food manufacturers pledged to reduce the calories as part of an agreement with a group of nonprofit organizations concerned about childhood obesity. Mrs. Obama earlier this year launched her own anti-obesity campaign.

To keep the companies accountable, the Robert Wood Johnson Foundation, a nonpartisan philanthropic and research organization that works to improve the nation's health, will evaluate how the groups' efforts affect the number of calories consumed by children and adolescents.