It's getting more expensive to eat right, concludes a first-of-its-kind study by two researchers at the University of Washington.

Earlier research by one of the researchers had already concluded that it cost more — based on an admittedly unusual measure, the cost per calorie — to eat healthful foods; this latest twist finds the gap is widening.

Adam Drewkowski, director of the university's Center for Public Health Nutrition, and Pablo Monsivias, a research fellow there, compared the price of foods that are less energy-dense to those that are more energy-dense in 2004 and 2006. Since "energy density" is rarely indicated on the shelf labels of local supermarkets, in pondering "less dense" foods, think fresh fruits and vegetables. Processed items that are high in refined grains, added sugars and added fats fall into the more-dense category.

Drewkowski and Monsivias first trooped through Seattle-area supermarkets checking out the prices in 2004, then repeated the survey in 2006. They report in the December edition of the Journal of the American Dietetic Association that while the general inflation rate for food in the U.S. rose 5 percent in those two years, prices rose 19.5 percent for lower-calorie chow.

Of course, their measure is just one way of parsing the dinner table. They note that years of consumer-oriented surveys, including one by the U.S. Department of Labor that produced the 5 percent figure above, have looked at food costs through a basket of products, where say falling produce prices may offset rising dairy costs. That, they feel, can mask the increasing cost of eating properly.

It's not, at least in the developed world, a matter of eating enough. "We are an overfed but undernourished nation," Drewkowski said in a release, which noted that people who dine regularly on energy-dense foods may consume more calories than they need while getting less nutrition than they bargained for.

With obesity on the rise, the researchers see their work as bulking up the evidence that it will take more than the bully pulpit to change the trend. "We need to focus on bigger-scale changes," Monsivais was quoted, "like the farm bill or other policy measures that can address the disparity in food costs."

They may have some powerful built-in listeners: The project was supported by two federal agencies, the Department of Agriculture and the National Institutes of Health.