It’s often taken as an article of faith in food policy discussions: Healthy eating is expensive. The Department of Agriculture recently set out to test whether that was actually the case. It compared prices of more than 4,439 food items, everything from sliced ham to canned peaches to potato chips.

The answer? It all hinges on how you measure “price.” Food policy analysts have often looked at cost-per-calorie, pricing out each unit of food energy. By that metric, fruit and vegetables tend to come out incredibly costly: A head of romaine lettuce has nothing, calorie-wise, on a candy bar.

(Marvin Joseph/The Washington Post)

But researchers have also started using a different metric: price by weight. They look at how much it costs to buy 100 grams of “edible weight,” which measures “the price of putting a given weight of a food item on a plate.” That comes out to about a quarter-pound of food.

When you compare foods on that metric, the Department of Agriculture finds, fruits and vegetables come out less expensive. It’s generally cheaper to buy 100 grams of produce than it is to buy 100 grams of a food high in fat or sugar (what the agency classifies as a “moderation food.”

In other words, buying your average-size apple tends to be less expensive than a two small bags of chips, which usually will add up to the quarter-pound metric.

Thus, the report concludes, “it is not possible to conclude that healthy foods are more expensive than less healthy foods.” Nor is it possible to conclude that healthy foods are less expensive. It is possible to conclude that we need to decide what we mean when we say a given food item is “more expensive.”