Fast food restaurants in the US have failed to raise the nutritional value of their dishes in 14 years, despite pledges to offer healthy choices, researchers say.
The global obesity crisis and rising levels of chronic diseases such as diabetes and strokes have put pressure on fast food chains to cut the salt, fat and sugar content of what they sell.
But a study funded by the Robert Wood Johnson Foundation's health eating programme and published in the American Journal of Preventive Medicine shows little has changed.
The nutritional quality of fast food meals, measured against the health eating index developed by the US Department of Agriculture, went up from 45 out of 100 in 1997/98 to just 48 in 2009/10.
The eight chains tested were McDonald's, Burger King, Wendy's, Taco Bell, KFC, Arby's, Jack in the Box and Dairy Queen.
Scores improved for meat, saturated fat and calories from solid fats and added sugars.
But scores dropped for milk/dairy and sodium. They did not change for fruit, vegetables, total grains and oils. KFC did best in increasing vegetables and total grains and decreasing saturated fats, solid fats and added sugars.
Margo Wootan, of the Centre for Science in the Public Interest, said restaurants had to change their thinking about the role their food plays in customers' diets and the impact on their health.
She suggested a range of measures, including reducing portion sizes and offering more fruit (not just juice) and vegetables, and making them default side dishes with meals. She also suggested removing sugar-sweetened drinks from children's menus.