Calorie
Food Nutrition · Physiology · Biochemistry
Say it: KAL-uh-ree
A calorie is a unit of energy, the heat needed to warm one gram of water by one degree Celsius; food energy is given in kilocalories, often written Calories.
Also: kilocalorie, kcal, cal
Definition
What is a calorie?
The calorie is a unit of energy. One small calorie (cal) is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius, and it is now fixed at 4.184 joules. The calorie used for food is a thousand times larger: the kilocalorie (kcal), sometimes written with a capital C as Calorie. When a food label lists 100 calories, it means 100 kilocalories.
In nutrition, calories measure the energy held in food that the body can release through metabolism. Carbohydrates and proteins supply about 4 kilocalories per gram, and fat about 9. The body spends this energy on basic functions such as breathing, keeping warm and pumping blood, as well as on digestion and physical activity, and it may need more during illness or fever. When intake exceeds what is used, the surplus is stored, mostly as fat; when intake falls short, the body draws on its stores.
Scientists increasingly express food energy in kilojoules, the SI unit, and food labels in many countries show both. Students meet calories in nutrition, in physiology when studying metabolic rate and in chemistry when measuring heat with a calorimeter.
Word parts
Where does the word “calorie” come from?
- calor-
- heatLatin calor
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Related
Terms that go with it
- MacronutrientA macronutrient is a nutrient needed in large amounts, namely carbohydrate, protein or fat, which together supply energy and the raw materials for growth.
- MetabolismMetabolism is the full set of chemical reactions in a cell or organism, both those that break molecules down for energy and those that build them up.
- Body mass indexBody mass index is a screening measure that relates body weight to height, found by dividing weight in kilograms by height in meters squared.
- CarbohydrateA carbohydrate is a sugar or a chain of sugars, such as starch or cellulose, built from carbon, hydrogen and oxygen and used for energy and structure.
- LipidA lipid is one of a varied group of biological molecules, including fats, oils, phospholipids, waxes and steroids, that do not dissolve in water.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Chemistry 2e, 5.1 Energy Basics
- NCI Dictionary of Cancer Terms: calorie
- MedlinePlus Medical Encyclopedia: Dietary fats explained
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