Making those calories count

You've probably heard of calories. You may have seen them listed on foods in the supermarket or on some restaunt menus.

But do you know what calories are?

“Maybe something that's not good for you,” said Georgi Hyde, 10, visiting the National Zoo from Georgia last month.

“Something that's not necessarily good if you have too many,” added her sister Virginia, 13.

The girls were half right. It is bad to eat too many calories. But understanding calories, and how many you need, is more complex than that.

How many calories you eat determines how much you weigh, and kids weigh more than they ever have. Today, one in three kids in the United States is overweight or obese, which means being severely overweight. That's triple the rate of 30 years ago, according to government statistics.

Life was different back then: Kids usually walked to and from school and played outside every afternoon. Today, more kids ride buses and play on computers. Kids also ate fewer snacks and smaller portions. The average child eats 30 percent more calories today than 40 years ago and gets less exercise. That adds up to extra weight.

Adults are worried because overweight children are more likely to develop health problems as teens or adults. First lady Michelle Obama started a program called Let's Move (www.letsmove.gov), which encourages activity and healthful eating. Some restaurants are adding calorie information to menus and more-healthful choices. McDonald's Happy Meals, for example, will soon contain apples and fewer french fries.

What exactly is a calorie? It's a measurement of how much energy your body gets from the food you eat. They are “literally the amount of fuel that food provides,” said Robert Post, one of the top nutritionists at the U.S. Department of Agriculture.

If you eat more calories than you need over a long period of time, those calories get stored in your body as fat cells, and you gain weight.

Not all kids need the same number of calories. If you play sports and ride your bike every day, you need more fuel (calories) than someone who is sitting at home reading. Boys also need more calories than girls because they tend to be bigger and have more muscle than girls.

So according to USDA, a 10-year-old girl who is 4 feet 10 inches tall, weighs 80 pounds and gets less than 30 minutes a day of intense exercise will need about 1,600 calories a day. But the same girl would need 2,200 calories if she got an hour of vigorous physical activity each day.

Everyone needs calories, but some calories are better than others.

For example, a medium-size banana and half of a glazed doughnut both have about 100 calories. We know what you're thinking — you'd pick the doughnut!

But look more closely: For 100 calories, that half a doughnut has almost nothing in it that's good for you, and it has a lot of fat, which is not good for your body.

The banana has almost no fat, but it is nutritious: It has lots of vitamins, minerals and fiber, which help your body and brain work well. A banana also makes you feel full for a longer time.

Did you change your mind?

The number of calories you consume each day isn't as important as the average calories you eat over a week or a month, Post said. So if you eat a ton of pizza and ice cream at the soccer party one day, try to eat a smaller, healthful meal with your family the next.

And even nutritionists say a healthful diet can include treats. “No one is saying you can't eat that doughnut, but you don't want that to be your every-day food,” Post said. “That's your sometimes food.”

Georgi and Virginia talked about that as they stood outside the zoo drinking vanilla Frappuccinos from Starbucks (“with caramel sauce!” they pointed out). The drinks were a special vacation treat for a hot day, Georgi said, adding, “We probably won't have dessert tonight.”