Calories: energy and enemy

One of dietitian Jill Weisenberger's clients kept a puzzling food journal: The calorie counts were all out of whack. The woman wrote that a tuna sandwich had 33 calories; an apple, 144.

Turns out the woman was mistaking a food-calorie book's index for a calorie chart.

The mistake is not too far-fetched, because few common health concepts are as baffling to us as "calorie." Calories are invisible, yet we try to count them and cut them. Food supplies them, but they're not nutrients.

"They're abstract," said Marion Nestle, a professor of nutrition at New York University, who says calories are "a mess" to explain. As a result, we're bizarrely wedded to a concept we know little about. Calories are the first thing people look for on the nutrition facts panel of food and beverages, but just 15 percent of Americans know how many they should be consuming. And less than one-third of us correctly say that "calories in general are most likely to cause weight gain."

Most of us simply want to know how many calories we need. But to truly grasp how calories can help you reach and maintain a healthy weight, it helps to know the basics.

The bottom line

Q. Are some calories more fattening than others? No. Some foods are more jam-packed with calories than others. You can eat a cup of pasta for about 220 calories, or you can eat about 4 cups of broccoli or you can munch on about one-quarter cup of nuts. They're all about the same calories, but the 4 cups of broccoli will tame your hunger more.

Q. How many calories do I need? You can get an estimate at www.mypyramid.gov.

Q. How can I cut calories without starving or hating what I eat? If you like vegetables, there's no reason to be hungry. They're relatively low in calories and filling because of their fiber and water content. Eat a couple of cups of them at dinner. It's a lot easier to decrease your potatoes and steak when you've got broccoli or zucchini to fill you up.

Try cooking at home. If takeout is your norm, commit to cooking just once or twice each week. And allow indulgences. There's no reason to give up your favorite foods - just eat smaller portions.

By the numbers

Most people need 2,000 to 3,000 calories a day, the range that maintains body weight in most people. Bigger or more active people need more. Smaller, more sedentary people need fewer.

The number of calories in 1 pound of body fat is 3,500.

Energy source

A calorie is the potential energy in food and the amount of energy the body uses. A calorie comes from three nutrients: carbohydrates, fats and proteins. Water, vitamins and minerals are all calorie-free. When we digest food, the nutrients are converted to glucose, or blood sugar. This powers the body. The food energy we don't need right away is stored as body fat.

Dietitian Jill Weisenberger tells her clients that calories are money: If you want extra money for something special, you might try to earn more or save.

"Think of calories the same way: If you want some extra for a special dessert or other treat, earn them by doing extra exercise, or save them from another time," said Weisenberger. "A 500-calorie slice of cheesecake will take an hour or more of really hard exercise. Or you could skip that second piece of buttered toast at breakfast, cut your juice in half and trade in your large sandwich for a smaller one."

Calculate it

How many calories do you burn during common activities? Find out at healthkey.com.