More than one quarter of American adults consume fast food two or more times per week. Specifically, 37.4 percent of sales of meals and snacks away from home happen at limited-service eating places such as fast food restaurants. Among children, the percentage of calories consumed at fast food chains has surpassed the amount consumed at school, becoming the largest contributor among food prepared away from home. 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 their offerings.

Yet, a study funded by the Robert Wood Johnson Foundation's health eating program shows that little has changed among fast food restaurants over nearly a decade and a half, despite their promises to voluntarily change and offer more healthy choices.

"Given the role of fast food in Americans' diets, restaurants are in a unique position to help improve the diet quality in the US by improving the nutritional quality of menu offerings," said Mary Hearst, lead investigator and associate professor of public health at St. Catherine University in Saint Paul, Minn.

Published in the American Journal of Preventive Medicine, the study's aim was to assess 14-year trends in the nutritional quality of menu offerings at eight fast food restaurant chains in the U.S.: McDonald's, Burger King, Wendy's, Taco Bell, Kentucky Fried Chicken (KFC), Arby's, Jack in the Box, and Dairy Queen.

Researchers obtained data on menu items and food and nutrient composition in 2011 from the University of Minnesota Nutrition Coordinating Center Food and Nutrient Database. In this database, ingredient and nutrition information for all foods sold by the fast food restaurants were updated biannually between 1997/1998 and 2009/2010. Healthy eating index (HEI)-2005 scores were calculated and compared over time for each restaurant menu.

Measuring the extent to which menu offerings were consistent with The Dietary Guidelines for Americans, the HEI-2005 scores reach a possible index total of 100 (healthiest).

The HEI-2005 score across all eight fast-food restaurants was 45 in 1997/1998. That score rose just three points to 48 in 2009/2010. Individually, restaurant scores in 1997/1998 ranged from 37 to 56 and in 2009/2010 ranged from 38 to 56. The HEI-2005 score improved in six restaurants and decreased in two.

Scores improved for meat, saturated fat, and calories from solid fats and added sugars. Scores dropped for milk/dairy and sodium. They remained the same for fruit, whole fruit, total vegetables, dark green and orange vegetables, legumes, total grains, whole grains, and oils. KFC did best in increasing vegetables and total grains and decreasing saturated fats, solid fats, and added sugars.

"Americans now spend 41% of their food dollars on foods eaten outside the home, up from 26% in 1970," said Margo Wootan of the Center for Science in the Public Interest, adding that restaurants need to change their thinking about the role their food plays in a customer's diet and health.

For some time now, efforts have been made to encourage the fast food industry to improve the nutritional quality of their meals. In California, New York, and some municipalities, policies limit the use of trans fatty acid-containing oils, margarines, and shortenings in food preparation. And, not all the changes have been motivated by government policy; some fast food restaurants have announced plans to improve nutritional quality on their own.

Wootan suggests a range of measures, including reducing portion sizes and making more vegetables and fruit (not just juice) as default side dishes with meals. She also suggests sugar-sweetened beverages to be removed from children's menus altogether and those on adult menus to be served in containers no bigger than 16 oz.