Reducing the trans-fatty acids in fries won't lower calorie counts. Outside experts say the move is risky because the formula could alter the taste of McDonald's famous fries. But if McDonald's succeeds, rivals Burger King and Wendy's would almost certainly be forced to try to follow. That could accelerate the development of healthier fast-food menus that consumers are clamoring for.

Trans-fatty acids — unsaturated fats created in processing vegetable oil for cooking — are now feared to be as much or more a risk for heart disease as saturated fats.