First Lady Michelle Obama joined Wal-Mart executives on Thursday at an event in Washington, D.C., to announce the launch of a broad initiative by the retailing giant to promote healthier foods.

Wal-Mart (NYSE: WMT) described several “key elements” of the program that will be introduced in all of its grocery stores. Wal-Mart is the largest U.S. grocer, and the world’s largest retailer.

Wal-Mart said it will reduce sodium by 25% and added sugars by 10% in its packaged foods by 2015. In addition, fresh fruits and vegetables will be made more affordable “through a variety of sourcing, pricing, and transportation and logistics initiatives that will drive unnecessary costs out of the supply chain,” the company said in a statement.

Wal-Mart also plans to lower prices on all products with reduced sodium , sugar or fat and improve the packaging on food products to help consumers make healthier choices.

The company also said it hopes to build stores in “underserved communities” to help improve access to fresh fruits and produce in those neighborhoods, and increase its charitable donations to organizations that support nutrition programs.

Wal-Mart is reportedly trying to raise its presence in urban areas, especially New York City, where the company’s penetration has been less successful than in rural areas.

Michelle Obama has made child obesity and improving the nation’s health her singular cause as first lady.

The First Lady said the announcement has "the potential to transform the marketplace and help Americans put healthier foods on their tables every single day."

"We are really gaining some momentum on this issue, we're beginning to see things move," she said at the event.

 “No family should have to choose between food that is healthier for them and food they can afford,” Bill Simon, Wal-Mart’s president and CEO, said in a statement.

Noting that Wal-Mart serves more than 140 million customer each week, Simon said the retailer is “uniquely positioned to make a difference by making food healthier and more affordable to everyone.”

Because of Wal-Mart’s size, it wields a tremendous amount of leverage over its suppliers. So if Wal-Mart tells the large food companies that supply its grocery stores to produce healthier products, those companies are likely to listen.

Competitors also keep an eye on Wal-Mart. In 2006, Wal-Mart introduced a $4 generic prescription drug program, leading other rival retailers to follow suit.

Wal-Mart has also introduced programs to reduce the amount of energy used and waste produced at its 8,700 retail outlets, a program generally praised by environmental groups.