Does it really cost more to buy healthful foods? Maybe not.

According to a new study by the U.S. Department of Agriculture, most fruits, vegetables, grains and other foods we think of as healthful are actually cheaper per portion than foods with higher amounts of sugar, salt and fat.

The report contradicts a rather long-standing belief among many folks that it’s more expensive to eat well – a belief bolstered by a number of previous studies that have found higher costs for healthful food choices.

So who’s right?

The answer seems to lie in how you calculate it. Most studies that examine food costs have used a standard metric: the cost per calorie. The USDA researchers decided to look at this a couple of different ways. They estimated the cost for each of more than 4,000 food items – 4,439, to be exact – and then crunched the numbers to come up with the price per calorie, price per edible weight and price per average portion consumed. They also calculated the cost of meeting the government’s daily ChooseMyPlate recommendations.

Here’s what they found:

- When the price is measured by the calorie, lower-calorie healthful foods do cost more – but this is mainly because of the math. It takes far more broccoli, for instance, to equal 500 calories than does a cinnamon roll.

- When the cost is measured by weight or serving size, healthful foods are generally the better bargain.

Our perception that the U.S. nutritional guidelines are unaffordable for many households may simply be a matter of the metrics, the study’s authors suggest. Price per calorie may be “one way, but not the only way, to measure the cost of a healthy diet,” they wrote.

Andrea Carlson, an economist and co-author of the study, told USA Today, “We have all heard that eating a healthy diet is expensive, and people have used that as an excuse for not eating a healthy diet… but healthy foods do not necessarily cost more than less healthy foods.”

She notes, “The price of potato chips is nearly twice as expensive as the price of carrots by portion size.”

There are many other factors, of course, that go into the consumer’s decisions in the grocery aisle. Some fresh fruits and vegetables genuinely are expensive, especially when they’re purchased out of season. For many people, the time and cost of preparation are a major consideration; it’s more work, after all, to rinse, trim, cut up and steam a head of broccoli than it is to pick up the phone and order a pizza. The metrics of cost per calorie vs. cost per serving or cost per edible weight also don’t address food availability, which is an entirely separate – and important – issue.

But there’s clearly more than one way of looking at food costs. Carlson suggests the best way to think of it is by portion size. “How much do you have to pay to put something on your plate?” she asks.