Kilocalorie (kcal)
The kilocalorie, symbolized as kcal, equals 1,000 calories and is often referred to as a “Calorie” with a capital C in food labeling. It measures the energy in food and human metabolism, helping dieticians, nutritionists, and consumers track intake. The kilocalorie became the standard unit of energy measurement as nutrition science linked energy measurement to diet. Most scientists now use joules, but kilocalories are still commonly used in reporting food energy.
Calorie (cal)
The calorie (cal) originated in the 19th century as a unit for quantifying heat energy. It was initially defined as the energy required to increase the temperature of one gram of water by one degree Celsius under standard atmospheric pressure. The calorie gained popularity in fields such as chemistry, physics, and nutrition. Despite not being an official SI unit, it remains prevalent on nutritional labels and in dietary contexts, particularly in the United States and Europe. Before the widespread adoption of the joule, the calorie played a significant role in standardizing energy measurements related to food and biological systems.