If you were given the choice of two similar-looking snack bars—one that cost $1 and one that cost $3—which would you assume was healthier? If you’re like most people, you’d probably pick the more expensive one.

The problem? Consumers jump to that conclusion across a wide variety of food categories, according to new research, even when there’s no supporting evidence that it’s true. In a series of five separate studies to be published next year in the Journal of Consumer Research, researchers show how our belief that healthy foods must cost more affects our decisions—about what we buy, what we eat, and even how seriously we take certain health issues.

In one experiment, for example, people who were told about an expensive but unfamiliar-sounding ingredient for eye health then rated that ingredient—and protecting their vision in general—as more important than those who were told that the same ingredient was lower-priced.

"It's concerning,” consumer psychologist and study co-author Rebecca Reczek, Ph.D., professor of marketing at The Ohio State University, said in a press release. “The findings suggest that price of food alone can impact our perceptions of what is healthy and even what health issues we should be concerned about.”

Of course, there definitely are situations in which “healthy” foods have a higher price point. Organic and gluten-free products are two examples. “It’s an easy thing to assume,” Reczek told RealSimple.com, “because we can all think of examples when healthy foods cost more and unhealthy foods, like fast-food combo meals, cost less.”

There are other food categories, however—granola bars, for example—in which price does not necessarily correlate with health or nutrition. And then there’s the fact that “healthy” can be defined in so many different (and not always accurate) ways, says Reczek, which means it's difficult to make blanket statements about price.

If you really want to put a number on it, a 2013 Harvard University study found that the healthiest diets cost about $1.50 a day more than the least healthy. But this new research wasn’t looking at the actual relationship between health and cost—only people’s perceptions of that relationship.

In one experiment, participants were asked to name a price for a new “granola bites” product. Those who were told the bites had an A- health grade thought the bites would be more expensive than those who were told they had a C grade. In a second experiment, participants rated a breakfast cracker as healthier when they told it was more expensive.

Then, researchers asked participants to buy a healthy lunch for a co-worker. When given the choice between two sandwiches—a Chicken Balsamic Wrap or a Roasted Chicken Wrap, both of which had clearly displayed ingredients—most of the well-intentioned shoppers bought whichever one was listed as more expensive.

“Rather than doing their own research, people are using the price as a signal,” Reczek says. “They’re relying on their intuition that healthy is expensive, and that acts as a shortcut to make up our minds and get us through the store more quickly.”

These results weren’t unexpected, but the researchers were surprised at how pervasive these beliefs were. The most interesting findings came from yet another experiment, in which participants were told to imagine choosing between four different trail mix options. One product was called the “Perfect Vision Mix,” which was touted as being “rich in Vitamin A” to some participants, and “rich in DHA” to others.

The researchers knew from previous studies that people tend to be familiar with Vitamin A, but not with DHA (an omega-3 fatty acid). They were curious how price point would affect people’s opinions about a well-known versus a not-so-well-known ingredient, so they told some participants that the Vision Mix was priced similarly to the other trail mix options, and told others that it was significantly pricier.

For people who saw the Vitamin A label, price point didn’t seem to matter; they rated Vitamin A as equally important to a healthy diet, regardless of the trail-mix cost. But in the group that saw the DHA label, people who were told the mix had a higher price point rated DHA as a more important part of their diet than those who were told it was a standard price.

And that’s not even the strangest part. When the DHA group was told that the ingredient helped prevent macular degeneration, the price of the trail mix also seemed to influence how concerned people were about this common eye disease, and how important a health issue they thought it was.

This difference was only seen in the DHA group, however. When an ingredient is well known, the authors hypothesize, consumers don’t need price points to serve as clues.

Assuming healthier equals pricier isn’t the end of the world, says Reczek, and a lot of times you might actually be right. But that doesn’t mean we should rely on these instincts all the time, she adds—because they do have the potential to lead us astray, and even affect our priorities.

“It’s pretty easy to combat,” she says, “but it requires stopping and thinking carefully and gathering some of your own research. Make an effort to back up your assumptions with evidence—like comparing nutrition labels or researching products before you get to the grocery store.”

Being a smart shopper may save you money, too, by helping you find exceptions to this presumed “rule.” Buying store-brand and bulk items, choosing frozen produce over fresh, and using more whole foods are just a few ways you can trim your supermarket bill and still fill up on good-for-you groceries.