NEW YORK (AP) — Want a side salad with that Big Mac?

McDonald's says it will start giving customers the choice of a salad, fruit or vegetable as a substitute for french fries in its value meals. The world's biggest hamburger chain was set to make the announcement at the Clinton Global Initiative in New York City, where CEO Don Thompson was slated to speak late in the afternoon.

The fast-food company also said it would use the packaging for its Happy Meals to promote healthier options. It said all advertising to kids will include a "fun nutrition or children's well-being" message.

The changes come as McDonald's faces criticism from health advocates who say it promotes bad eating habits. McDonald's, based in Oak Brook, Ill., is also trying to shake its fast-food image to keep up with shifting tastes. Chains such as Chipotle and Panera, for example, have become more popular because they're seen as offering higher quality food for a little extra money.

To keep pace, McDonald's recently introduced the option to get substitute egg-whites in all its breakfast sandwiches. The chain also rolled out chicken wraps, which are partly intended to go after people who might head to places such as Subway instead.

It's too early to say what impact the changes will have. Late last year, the company reported its first monthly sales decline in nearly a decade. The company has struggled to push up the figure ever since.

In August, sales edged up just 0.2 percent at restaurant open at least a year. The metric is a key indicator of health because it strips out the volatility of newly opened and closed locations.

McDonald's has also been under scrutiny for its marketing to children. A recent study by the Robert Wood Johnson Foundation, for example, found that the chain's ads targeting children often emphasize toy giveaways and movie tie-ins, rather than food.

McDonald's Corp., which has more than 34,000 locations around the world, said the changes will take place in 20 major markets. They will be in place in up to half the markets within three years and all the designated regions by 2020, the company said.

The markets include Argentina, Australia, Brazil, Canada, China, France, Germany, Hong Kong, Italy, Japan, the Netherlands, Poland, Russia, Spain, Sweden, Switzerland, Taiwan, the United Kingdom and the United States.