The obesity epidemic is caused by many factors, but nutritionists say one main reason is how dependent we've become on eating out.
When you cook at home, most ingredients in your cupboard have mandatory FDA nutrition labels. But restaurants are exempt, so when you place your order you can only guesstimate how many calories you'll be putting in your mouth.
Now one of the most powerful health officials in the country wants to change that by forcing chain restaurants like McDonald's and Wendy's to spell out exactly how fattening their food is -- right when you decide what to order.
As correspondent Lesley Stahl reports, the idea is gaining support nationwide, but also faces fierce opposition from the restaurant industry itself.
It all started last December, when New York City passed a regulation requiring chain restaurants to post the calories of their food right on their menus or menu boards.
"We think it will encourage people to choose lower calorie options because that information will be available to them," explains New York's health commissioner, Thomas Frieden.
Frieden is in charge of regulating New York City's $11 billion restaurant market, and tells Stahl the restaurants "really hate" having to do this. "There's no question about that," he says.
"Now most of the chains have the nutritional information somewhere," Stahl points out.
"Usually on a Web site hidden somewhere," Frieden says. "Or on the package liner or the tray liner, after you've bought the product."
Asked why that isn't enough, Frieden argues, "No one is going to check a Web site, then go to the local burger joint and decide what to buy. People do look at the menu board. The menu board is the most prominent thing within a fast food restaurant."
The regulation would cover mainly big chains, like KFC, Burger King, McDonald's and Starbucks.
Frieden wants people to see as they order that some combo meals, like one from Burger King, pack 2,200 calories -- more calories than many adults need in a day. Some Starbucks drinks are more fattening than Big Macs. And even what seems good for you might be anything but.
"You might think that tuna salad, because it says it's salad, is healthier. But you might see it's many more calories than a roast beef sandwich. And you might prefer the roast beef sandwich, too. You were having the tuna salad because you thought it was healthy," Frieden explains.
Brian Wansink is a nutrition and marketing professor at Cornell University. He uses the mall as a laboratory, observing the food-court crowd like other scientists study rare tribes.
Wansink, who even wrote a book called "Mindless Eating," finds that people always underestimate calories, but they get it especially wrong when they're eating something they think is healthy.
On one of his recent "observation trips," Wansink concentrated on meals from Subway, which markets itself as the healthy fast-food alternative. He asked people to estimate the calories of an especially caloric combo: a foot-long Subway sandwich with mayo, chips and juice.
"Now for this you estimated that it had about 300 calories," Wansink pointed out to a man. "In reality it has 1,390."
"When people are eating in a restaurant that they think is healthy, people grossly underestimate how much they eat by about 50 percent," Wansink explains.
"So they eat much more than they think they're eating?" Stahl asks.
"By about twice as much," he says. "That mayonnaise you ate probably was not healthy. The extra cookie you ate probably wasn't that healthy. The chips probably weren't that healthy."
"Well, let's say for instance that we would have had the calories listed on the menu when you ordered something like that. Would that influence what you ordered?" Wansink asked a man.
"Absolutely. I don't think I would have gotten it. I mean, 1,350 calories for a Subway," the man replied.