Wal-Mart Stores Inc unveiled a plan to promote healthier and more affordable foods at its stores, a move supported by U.S. first lady Michelle Obama and one that could push food companies to overhaul some products.

The move comes as the world's largest retailer tries to overcome political and union opposition to its expansion in urban areas like New York City, Chicago and Washington, D.C., by touting its ability to bring lower priced fruits and vegetables and other healthy foods to areas that lack traditional grocery chains.

Mrs. Obama joined Wal-Mart executives as they announced details of the plan in Washington on Thursday. She said she was thrilled about Wal-Mart's new nutrition plan, adding: I believe this charter is a huge victory for folks all across this country.

Bill Simon, president and CEO of Wal-Mart's U.S. business, said in a statement on the company's web site ahead of the event that no family should have to choose between food that is healthier for them and food they can afford,

Mrs. Obama leads an administration initiative to combat child obesity. She has pushed food makers to quickly reformulate food to make it healthier.

Wal-Mart plans to make thousands of its packaged foods lower in unhealthy salts, fats and sugars, and to drop prices on fruits and vegetables.

Wal-Mart has already discussed its goal to bring lower-priced, healthier foods to urban areas known as food deserts that do not have traditional grocery stores, as it tries to expand in urban areas.

Thursday's announcement comes three months after Wal-Mart announced plans to double the sales of fresh produce from local farms in its U.S. stores by the end of 2015. That move was part of a broader strategy to revamp its global produce supply chain.

Wal-Mart is the largest seller of food in the United States, so any move it makes can have a ripple effect in the food supply chain. It also has the potential to impact everyone from farmers to grocery stores, drugstores and dollar stores, who have been beefing up their food offerings.

The battle for food spending is heating up, even before Wal-Mart's new initiative. Target Corp, Family Dollar, Walgreen Co and others have dedicated more space to food in their stores. They hope that by providing a wider variety of items people will come into their stores more often, and spend more when they visit.

Such shifts in the food industry have added pressure to grocery stores, which already face soaring costs.

Wal-Mart sells a wide variety of food from companies such as Kraft, Unilever and PepsiCo and sells food under its Great Value private brand.

Changes that Wal-Mart spearheads spread much further than its store doors. A few years ago, detergent makers such as Procter & Gamble Co quickly reformulated their products to remove water and reduce package sizes after Wal-Mart pushed suppliers for more environmentally-friendly products. The manufacturers absorbed millions of dollars in costs to meet the changes Wal-Mart was asking for.

Wal-Mart shares were up 83 cents, of 1.5 percent, at $55.86 on Thursday on the New York Stock Exchange.

(Reporting by Jessica Wohl, additional reporting by Sakthi Prasad in Bangalore, editing by Dave Zimmerman)

Michelle Obama Walmart