Calorie

A calorie is a metric unit of energy, defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius. Its imperial counterpart is a British thermal unit or BTU. One calorie equals approximately 0.00396567 BTUs.

In food, calories are typically conveyed in kilocalories, with 1000 calories equal to 1 calorie, but labeled as simply a calorie. The body obtains calories for its energy needs from dietary fat, protein, alcohol, and most carbohydrates except for dietary fiber.