WASHINGTON — Eating healthy foods is not necessarily more expensive than eating less healthy foods, according to a new report from the Economic Research Service of the U.S. Department of Agriculture. In fact, the findings suggest the metric used to measure the price of food items tended to have a large effect on which foods were more expensive.

The report, “Are healthy foods really more expensive? It depends on how you measure the price,” was posted May 16 on the E.R.S. web site (www.ers.usda.gov).

To assure a balanced assessment, the E.R.S. study compared the prices of healthy and less healthy foods using three price metrics: the price per calorie, per edible gram and per average portion. The E.R.S. report defined healthy foods as containing an amount of food in at least one of the major food groups (vegetables, fruits, grains, dairy and protein foods) equal to at least half the portion size that the Dietary Guidelines for Americans 2010 uses for measuring the nutrients in that food, and containing only moderate amounts of saturated fats, added sugars and sodium.

“Foods low in calories for a given weight appear to have a higher price when the price is measured per calorie,” the E.R.S. said. “For example, vegetables and fruits, which are low in calories, tend to be a relatively expensive way to purchase food energy.

“Conversely, less healthy foods (called ‘moderation foods’ in this report) — especially those high in saturated fat and added sugar — tend to be high in calories and to have a low price per calorie.

“When measured on the basis of edible weight or average portion size, grains, vegetables, fruit and dairy foods are less expensive than most protein foods and foods high in saturated fat, added sugars and/or sodium.

“In following the food group recommendations at ChooseMyPlate.gov, it is less costly to meet the grains, dairy and fruit recommendations than those for vegetables or protein foods.”

Study lead author Andrea Carlson in a May 16 blog posting added, “We found that the price measure used has a large effect on which foods are more expensive. If we use price per calorie, fruits and vegetables tend to be more expensive than less healthy foods. In contrast, if we use price per edible weight or per average amount eaten, then grains, vegetables, fruits and dairy foods are less expensive than most protein foods and less healthy foods.”

The E.R.S. estimated the cost of 4,439 food items as part of the study, which drew on three data sets: the National Health and Nutrition Examination Survey to estimate the types and quantities of foods consumed; the U.S.D.A.’s Center for Nutrition Policy and Promotion foods prices database for food prices; and the U.S.D.A. Food Pattern Equivalent Database (formerly known as the MyPyramid Equivalent Database) for information on food group classification, saturated fat, added sugars and sodium content.