Now it's up to the patrons of Big Macs and fries to decide how big an appetite they have for a healthier McDonald's, which unveiled its latest low-fat offerings yesterday as part of a new marketing blitz.

"If I want to eat healthy, I'll eat at home," said 33-year-old Chuck Horton as he lunched at a crowded McDonald's in Garrisonville, Va.

"I come to McDonald's for one reason: the fries. ... I think this healthy eating thing has gone too far," he said.

Horton and other fast-food lovers need not panic. The restaurant giant isn't changing the recipe for its burgers and fries — the financial meat-and-potatoes of its $6 billion-a-year U.S. operation — or dropping its triple-thick shakes.

A target of obesity lawsuits and a magnet for criticism that fast food is bad for you, McDonald's Corp. is simply trying to meet health issues head-on and show that it, like many of its customers, has become more diet-conscious. Top executives announced the new campaign in Washington, where U.S. Health and Human Services Secretary Tommy Thompson applauded McDonald's for promoting balanced eating and exercise.

The new "Go Active!" adult Happy Meals will be available in all 13,600 U.S. McDonald's on May 6, accompanied by brochures offering some gentle exercise advice: Walk more. Other changes will soon follow.

"We want to help adults achieve the right balance between their daily calorie intake and physical activity, and to help children adopt active, balanced lifestyle habits early on," said Mike Roberts, president of McDonald's U.S. business.

Food-industry experts credit McDonald's with taking steps in the right direction but voiced some skepticism about its new pro-health stance.

Bob Goldin, an analyst for the restaurant consulting firm Technomic Inc. in Chicago, called it ironic that the world's leading purveyor of fast food, "which has a lot of calories, fat, sodium, you name it," is trying to portray itself differently.

"Their menu has inched toward healthier, it certainly hasn't leapfrogged," he said.

The introduction of adult Happy Meals is just one in a series of related moves by McDonald's, which introduced white-meat chicken nuggets late last year and is phasing out super-sizing.

As part of the campaign, the company said that in June it will roll out healthier choices in its Happy Meals for kids nationwide, such as the option to substitute apple slices and juice for fries and soft drink.

It also will distribute brochures telling customers how to modify their McDonald's orders for lower fat, calories and carbohydrates, such as by skipping the cheese or bun. The promotion has been employed at its New York-region restaurants since January.

Also new: low-fat salad dressing, a fourth variety of salad, and providing nutrition information on Happy Meal packages starting in test markets.

Obesity and diet concerns have been forcing sweeping changes in the U.S. food and restaurant industries. McDonald's introduced entree salads in the United States about a year ago, helping lead to a surge in long-lagging U.S. sales, and has been moving to add some healthier options to its restaurants worldwide, including salads in Europe this spring. Fitness whiz Bob Greene has signed on to help the company promote walking.

Its competitors, too, have been responding to consumer concerns. Wendy's added entree salads well before McDonald's, and Burger King started promoting bunless burgers in January.

Blaming McDonald's for Americans' rising obesity and physical inactivity is "not reflective of reality," Roberts said in an interview.