The basic facts of calories


A calorie is . . .

A unit of energy. First described in the 1800s, a calorie is technically the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius. But in the health and nutrition world, a calorie is the potential energy in food and the amount of energy the body uses, according to the American Dietetic Assn.'s Complete Food and Nutrition Guide.

Calorie facts: An article in the Feb. 15 Health section describing the basic facts of calories defined a calorie as the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius. However, the unit of measure used to state the energy content of food, which is what the article referred to, is the so-called large calorie: the amount of heat needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. —

“We need this reference value in the same way we’d need to know how many pieces of wood to build a certain size house,” said San Diego registered dietitian Janice Baker, a certified diabetes educator. “Everyone’s body needs different amounts of energy based on height, weight, activity level, age and other factors. A calorie is not good or bad. It just is.”

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 released, absorbed into the bloodstream and converted to glucose, or blood sugar. This powers the body, allowing us to shiver, blink, remember, breathe and run. The food energy we don’t need right away is stored as body fat, regardless of the nutrient it comes from. That means excess carbs are no more fattening than additional calories from any source, including fats and proteins.

Calories can help us lose weight if . . .

We burn more calories than we take in. “It doesn’t matter when you eat them; your body uses the calories from ice cream in the same way, whether you eat at 10 p.m. or 10 a.m. But if you deliberately eat lightly during the day to have a good dinner, then hunger often gets out of control and you overeat,” said Susan Roberts, director of the Energy Metabolism Laboratory at Tufts University’s Jean Mayer USDA Human Nutrition Research Center on Aging. “Pacing calories is an important component of successful dieting.”

Registered dietitian Jill Weisenberger tells her clients that calories are money. “You have a certain amount in your budget, and if you spend too much, you go into debt. If you take more than your calorie allowance, you get fat.”

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,” Weisenberger said. “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. Or you could combine dietary and exercise changes.”

Now for a look at the

numbers . . .

2,000: A general estimate of the daily calories needed to maintain body weight. Bigger or more active people need more. Smaller, more sedentary people need fewer.

3,500: Number of calories in 1 pound of body fat.