That may help explain the findings of a study that appeared in the Journal of Adolescent Health, in which researchers compared the eating habits of teens who ate at Subway and McDonald's.

They chose those two eateries because those were the places teens named when asked what places they considered healthy and unhealthy, respectively. But when researchers measured what teenagers actually bought at Subway and McDonald's – as opposed to the full scope of what those eateries actually offered – they found that those teenagers were eating, on average, virtually the same number of calories, no matter where they ate: 1,038 calories per teen at McDonald's, compared to 955 at Subway.

Fast-food restaurants' touting healthy options on their menu is nothing new. Despite a relatively recent push to promote some of its healthier menu items, McDonald's has gotten a lot of negative press over the years for its food's unhealthiness (and for targeting children in its advertising). But Subway has maintained a fairly sterling reputation as a healthy option for consumers needing a quick bite. (It was named on lists of the best healthy fast-food options here, here and here – then again, some items from McDonald's made some of those lists, too.)

While there may be plenty of green pins in the map, Dr. Lenard Lesser, the study's lead author, said he wasn't measuring what the restaurants offered teens. He was measuring what teens actually ordered.

The study

"Both restaurants are trying to change their menu to increase the 'healthy factor,'" said Lesser, who currently works as a doctor of family medicine at Palo Alto Medical Foundation Research Institute and was a Robert Wood Johnson Foundation Clinical Scholar with UCLA's medical and public health programs when he led the study. But that was largely irrelevant to teenagers' eating habits: "Our study found no real difference in what they were ordering," he added.

Among Lesser and his colleagues' other findings:

The sandwiches that teens bought at Subway had an average of 784 calories, compared to 572 at McDonald's.

On average, sodium intake was 2,149 grams at Subway and 1,829 grams at McDonald's.

Participants ate 102 grams of carbohydrates at Subway, compared to 128 at McDonald's.

Side items from Subway tended to add about 35 calories to the teenagers' meals, compared to side items from McDonald's, which added an average of 201 calories.

For their part, restaurants like McDonald's say they're committed to consumer choice: They'll offer healthy menu items and then let the consumer decide if she or he wants to buy them.

Lesser says restaurants ought to go further than that, and promote their menu items at least equally.

"The message that I'm giving is going to be overridden by the marketing machine of these restaurants," he said. "So the restaurants really have to focus on advertising healthier foods and promote healthier foods as much they promote [their other] food."

That's something he believes fast-food restaurants can do effectively, and not at a loss, he added. In the meantime, Lesser said, there are some stop-gap measures teens can take to combat the unhealthiness of orders.

"At McDonald's, they should really try to avoid ordering the sugary drinks and avoid ordering the fries," he said. "At Subway, opt for the six-inch sub … and ask for half the meat and extra veggies on the sandwich."