LOS ANGELES (Reuters) - McDonald's Corp. is putting the pot-bellied green star of "Shrek" movies on a diet in a new campaign that features the restaurant chain's apple slices and salads rather than its burgers and fries.

On Tuesday, McDonald's and DreamWorks Animation SKG Inc., the studio behind the upcoming "Shrek the Third" movie, unveiled a promotion in which Shrek, Donkey and other characters from the animated film will be used to sell Happy Meals and other McDonald's food.

But unlike previous movie tie-ins, McDonald's will use Shrek to feature its salads, milk, apple slices and other products introduced in the last 3 years as the No. 1 restaurant company faced mounting criticism its food was not only unhealthy, but also contributing to the increase in overweight kids in the United States.

A Happy Meal with Apple Dippers, all-white-meat chicken McNuggets, and low-fat milk will be featured in television commercials and on posters in McDonald's restaurants. Shrek will also appear on packaging for the milk and apples.

While the apples, milk, salads and other featured products have been on McDonald's menu for more than a year, Chief Marketing Officer Mary Dillon said the company still had "opportunities to drive awareness both with parents and kids about these offerings."

McDonald's will also use Shrek to promote physical activity through games on its Web sites that require both online and offline play, Dillon said.

The company would not disclose how many Happy Meals it sells with apple slices versus those with French fries.

The decision to limit the Shrek characters to healthier products was taken by both corporations, DreamWorks spokesman Bob Feldman said.

Shrek also appears in a series of public service announcements by the U.S. Department of Health & Human Services that encourage kids to be physically active.

The department has come under fire from The Campaign for a Commercial-Free Childhood, which opposes marketing to children, for using Shrek at the same time he is to appear on products such as Happy Meals, M&M's chocolates and Kellogg Co. cereals such as Froot Loops and Frosted Flakes.

DreamWorks' Feldman said candy is a treat and how much a child eats is a matter of parental responsibility.

McDonald's Shrek promotion begins May 11 in the United States and will last about four weeks. "Shrek the Third" opens in the United States on May 18.