Wal-Mart, the nation's largest retailer and grocer, said Thursday that it would launch an aggressive initiative to make its food products more healthful and affordable and would build new stores in underserved areas.

As part of First Lady Michelle Obama's signature campaign to fight childhood obesity, Wal-Mart said it would reduce sodium by 25 percent, lower added sugars by 10 percent and remove all industrially produced trans fats in the packaged foods it sells to its roughly 140 million customers each week. It also said it would work with its distributors and farmers to lower prices on fresh fruits and vegetables, estimating that it would save customers $1 billion a year.

Wal-Mart isn't the first to improve the healthiness of its products. But it sells more groceries than any other company in the country, and it works with a vast network of more than 60,000 suppliers. One move by Wal-Mart can ripple throughout the industry. And the company has grown increasingly bold in tackling social and political issues.

"We are obviously conscious about where we walk and who we walk with," said Sam Kass, assistant White House chef and coordinator of food initiatives. "But it was clear that this is potentially transformative."

The First Lady, who joined Wal-Mart executives in making the announcement in Washington, called it a victory for parents and children that will give families more information and more opportunities to eat more healthy foods. "When I see a company like Wal-Mart launch an initiative like this, I feel more hopeful than ever before," she said. "We can improve how we make and sell food in this country."

She said that because of company's size, the move "has the potential to transform the marketplace. ... They are changing how the entire food industry does business."

The announcement amounted to a very public display of affection for a company that had long been a thorn in the side of Democrats. Five years ago, Wal-Mart was in the midst of a bruising battle with labor groups that accused it of paying low wages and providing stingy health benefits. Michelle Obama resigned from the board of a Wal-Mart supplier during her husband's campaign. And Obama himself told supporters at an AFL-CIO forum in 2007 that he would not shop at Wal-Mart.

In recent years, Wal-Mart has reached out to Democrats. During the debate over health care, it broke ranks with business groups by supporting the mandate for employers in Obama's health care legislation. It has emerged as a leader in sustainability and carbon reduction, improving fuel efficiency for its supply trucks and vowing to eventually produce zero waste.

Healthful foods skyrocketed to the top of the company's priority list once the First Lady made it hers by launching the Let's Move campaign. Wal-Mart and Obama began talking about a year ago. Company leaders cited Michelle Obama as the "catalyst that helped make today's announcement a reality."

Easy to identify

The retailer said it has already met its goal in as much as a quarter of the products in its private-label brand, Great Value. Some of the food items being targeted include those that consumers don't expect to come with a lot of sodium or sugar such as salad dressing, lunch meat or box dinners, said Andrea Thomas, senior vice president of sustainability.

The company plans to tag products that meet the goals so customers can easily identify them. It also says it will lower prices on healthful foods, such as whole-wheat pasta, so that they cost the same as traditional versions. "No family should have to choose between food that is healthier for them and food they can afford," said Bill Simon, Wal-Mart's CEO.

Obama already has won pledges from companies including Kraft, Pepsi and Golden Valley-based General Mills to reduce calories by changing recipes or cutting portion sizes. General Mills said in November that it had boosted whole grains, cut sugar and made several other healthful changes to products that accounted for 25 percent of its U.S. sales in the past year.

Eden Prairie-based Supervalu Inc., one of the nation's largest supermarket companies, said it already offers many private label items that are low in salt or sugar. And Wal-Mart rival Target has increased its fresh food and grocery offerings.

Nutrition experts say Wal-Mart's changes could have a big impact on the affordability of healthy food and the health of U.S. families and children.

Almost like the FDA?

Some say the company has almost as much power as federal regulators to shape the marketplace. "Wal-Mart is in a position almost like the Food and Drug Administration," said Michael Jacobson, executive director of Center for Science in the Public Interest. "I think it really pushes the food industry in the right direction."

For example, in 2006, Wal-Mart introduced a $4 generic prescription drug program, leading rival retailers to follow suit.

But Wal-Mart is pushing only so far. He noted that Wal-Mart is not proposing to tackle the problem of added sugars in soft drinks, which experts regard as a major contributor to childhood obesity. And he said it would be "nice if Wal-Mart's timeline were speedier" than five years.

Staff writer Mike Hughlett, Washington Post, Los Angeles Times, Bloomberg, MarketWatch and New York Times contributed to this report.