ST. PAUL, MINN. — The nutritional quality of food offered at fast-food restaurant chains has improved only moderately over the past 14 years, according to new research funded by the Robert Wood Johnson Foundation’s Healthy Eating Research program and published in the American Journal of Preventive Medicine.

“Despite qualitative evidence that the fast-food industry is making improvements to the nutritional quality of at least some of their menu items, a quantitative evaluation of trends in the nutritional quality of fast food available in the marketplace was lacking,” said Mary Hearst, Ph.D., MPH, associate professor of public health at St. Catherine University in St. Paul, Minn., and lead investigator of the study. “This is the first study to quantitatively evaluate whether fast-food restaurant chains have improved the nutritional quality of their U.S. menu offerings over a period of time during which they have been encouraged to do so by governmental and nongovernmental agencies.”

Using data from 1997-1998 to 2009-2010 from the University of Minnesota Nutrition Coordinating Center Food and Nutrient Database, the researchers calculated Healthy Eating Index (H.E.I.)-2005 scores from eight restaurants (Arby’s, Burger King, Dairy Queen, Jack in the Box, Kentucky Fried Chicken, McDonald’s, Taco Bell and Wendy’s).

The U.S. Department of Agriculture developed the H.E.I.-2005 to evaluate the extent to which an individual’s diet is consistent with the 2005 Dietary Guidelines for Americans. The U.S.D.A. reported the mean H.E.I.-2005 score for the U.S. population was 57.5 out of 100.

The researchers found that of a possible index total of 100 (healthiest), the H.E.I.-2005 score across all eight fast-food restaurants was 48 in 2009-2010, up from 45 in 1997-1998. Individually, the restaurant scores in 2009-2010 ranged from a low of 38 to a high of 56. This compared with a range of 37 to 56 in 1997-1998.

Six of the eight restaurants studied improved the nutritional quality of their menu offerings, with the greatest improvement during the 14-year period registered by Kentucky Fried Chicken, up 9 points, followed by Jack in the Box, up 7 points. Burger King and Wendy’s were the only two fast-food chains not to post a gain in their comparative H.E.I.-2005 score over the 14-year period, the study noted.

The researchers said Wendy’s decreased the amount of vegetables and total grains offered, whereas saturated fats and calories from solid fats and sugars increased. At Burger King, scores decreased for meat, milk/dairy, sodium, and calories from solid fats and sugars, the researchers said.

In terms of the actual components making up nutritional quality, the study showed the greatest improvements were seen in the increase of meats/beans, decrease in saturated fat, and decrease in the proportion of calories from solid fats and added sugars. The fruit, whole fruit, total vegetables, dark green and orange vegetables and legumes, total grains, whole grains and oils component scores did not change during the period. A lower score was noted for two H.E.I.-2005 components: milk/dairy and sodium.

“Given the role of fast food in Americans’ diets, restaurants are in a unique position to help improve the diet quality in the U.S. by improving the nutritional quality of menu offerings,” Dr. Hearst said. “Modest improvements in average nutritional quality of menu offerings across eight fast-food restaurant chains were observed, which is consistent with both legislative efforts (e.g., banning trans fat) and the industry’s own statements about creating healthier menu options. However, considering that fast food is ubiquitous in the U.S. diet, there is much room for improvement.”

Responding to the study, Joan Rector McGlockton, vice-president of industry affairs and food policy at the National Restaurant Association, said, “Nutrition is a strong trend across the industry, including quick-service, and significant progress has been made just in the last few years alone. The National Restaurant Association’s 2013 Restaurant Industry Forecast shows that over 85% of adults say there are more healthy options at restaurants than there were two years ago. Consumers choose to dine out for many occasions and restaurants provide an array of choices to meet their customers’ preferences, including a growing selection of healthful menu options.”