NEW YORK (Reuters Health) - The price of fruits and vegetables is climbing faster than inflation, while junk food is actually becoming cheaper, the findings of a new study suggest.

Using retail prices at major supermarket chains in Seattle, researchers at the University of Washington found that low-calorie, nutrient-rich foods -- mainly fruits and vegetables -- were far more expensive, calorie for calorie, than sweets and snack foods.

Moreover, the average price of the lowest-calorie foods -- including green vegetables, tomatoes and berries -- increased by almost 20 percent over 2 years. In contrast, in the same time period there was a 2-percent dip in the cost of the most calorie-laden fare, such as butter, potato chips, cookies and candy bars.

The findings, published in the Journal of the American Dietetic Association, highlight a key obstacle to healthy eating. And they may help explain why obesity rates are highest among the poorest Americans, according to the researchers.

“Whereas (calorie)-dense foods remain the most affordable option, the price of the recommended healthful foods of lower (calorie) density has disproportionately increased,” write Drs. Pablo Monsivais and Adam Drewnowski.

They add that, along with encouraging Americans to change their personal behavior, the government may need to make policy shifts that help people eat more healthful foods -- such as changes in the way the government subsidizes the agricultural industry.

In their study, the researchers examined the prices of 372 foods and beverages at Seattle supermarket chains in 2004 and 2006.

They found that snack foods, sweets and fatty foods offered the most bang for a shopper’s buck. Whereas the price of the lowest-calorie fruits and vegetables was more than $18.16 per 1,000 calories, the most calorie-rich foods cost $1.76 per 1,000 calories.

The 20-percent increase in the cost of the lowest-calorie foods may be putting healthful foods out of reach for those Americans who need these foods the most, according to the researchers.

“The finding that (calorie)-dense foods are not only the least expensive, but also most resistant to inflation, may also help explain why the highest rates of obesity continue to be observed among groups of limited economic means,” they write.

SOURCE: Journal of the American Dietetic Association, December 2007.