Fast food is an undeniable part of American culture. We've probably all encountered the McDonald's "I'm Lovin' It" jingle and the white-goateed Colonel Sanders of KFC at least once, if not hundreds, of times.

The big fast-food chains market their foods to us constantly. And our children see, on average, three to five fast-food ads per day.

So perhaps the the Centers for Disease Control and Prevention's new findings shouldn't come as a surprise.

"About 34 percent of all children and adolescents, aged 2 to 19, consume fast food on a given day," says Cheryl Fryar of the CDC's National Center for Health Statistics.

In other words, every day about 1 in 3 kids in the U.S. is chowing down on fries, burgers, pizza or other fast-food favorites.

And despite all the promptings to eat more healthfully, this rate of fast-food consumption hasn't budged in the past 15 years.

So even if McDonald's bottom line is hurtingright now, it seems Americans' overall appetite for fast food is as strong as ever. The CDC has found that adult consumption of fast food mirrors what it is seeing in kids.

Part of the appeal is price. For example, a burger or ice cream off the dollar or value menu is cheap. And c'mon, admit it: French fries can be hard to resist. Fast-food menus are geared to our most basic desires.

"We're programmed to seek sweet and salty foods, and fast food knows how to pander to those cravings," says pediatrician Stephen Pont at Dell Children's Medical Center of Central Texas, who is chairman of the American Academy of Pediatrics section on obesity.

And once kids have a habit of eating these foods, it's hard to break it.

"A particular challenge with teenagers is that they all feel invincible, and they're not as sensitive to the long-term impacts of [diet] on their health," Pont says.

So it seems fast food's trifecta of marketing, affordability and taste has a hold on America's youth. And even as fast-food giant McDonald's is increasingly competing with fast-casual chains such as Five Guys and Chipotle, the basic formula remains the same.

"I think it speaks to how big a role fast food plays in how we eat in America," says Julia Wolfson, a doctoral student and researcher at the Johns Hopkins Bloomberg School of Public Health.

Shifting our preferences away from salt, sugar and fat is no small task.

But, Wolfson says, there seems to be some progress. She points to evidence that the major fast-food chains are trying to make their menus more healthful.

McDonald's, for instance, downsized its Happy Meal portions. And it has introduced new kinds of salads and added kale to its breakfast bowls in some locations.

As we've reported, Wolfson's research points to changes across the board. "We have found that fast-food restaurants have been introducing new menu items that are on average 60 calories lower than old menu items," Wolfson says.

Wolfson says if this trend continues, it could make a difference.

Kids are eating about 190 calories per day in fast-food calories. So if you think about shaving 60 calories off, "that's a good chunk out of the total."

Of course, there's lots of room for improvement.

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