Marcel Maillet, age 12, of Oromocto, New Brunswick, Canada, for her question:

WHAT EXACTLY IS A CALORIE?

A calorie is a unit used to measure heat energy in the metric system of measurement. One calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius.

Scientists measure the amount of heat produced with an instrument called a calorimeter.

A calorimeter is used to measure the amount of heat given off by different foods when they burn. The instrument tells how much energy a certain food has when it is completely used by the body. Food scientists measure the heat produced in the calorimeter in kilogram calories, but they report the measurements as "food calories" or simply as calories.

Calorie comes from the Latin word calor, which means heat.