Calories are a unit of measurement used to quantify energy. In the context of nutrition and food, a calorie refers specifically to the amount of energy that food provides when consumed. More technically, a calorie is defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.
There are two types of calories commonly referenced in nutrition:
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Calorie (small calorie or gram calorie): This is the basic unit that measures energy in terms of heating water, as mentioned above.
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Kilocalorie (Calorie or large calorie): This is typically what is referred to when discussing dietary energy. One kilocalorie (1 kcal) is equivalent to 1,000 small calories and is the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. In everyday terms, when we discuss food energy, we use "Calories" with a capital "C," which generally means kilocalories.
Calories in food come from three primary macronutrients:
- Carbohydrates: Provide about 4 calories per gram.
- Proteins: Provide about 4 calories per gram.
- Fats: Provide about 9 calories per gram.
Understanding calories is essential for managing energy balance, which has implications for weight maintenance, weight loss, and overall health. If the number of calories consumed exceeds the number of calories expended through physical activity and metabolic processes, a person can gain weight. Conversely, consuming fewer calories than what is burned can lead to weight loss.
In summary, calories are a fundamental concept in nutrition, providing a way to measure the energy content of food and understand its role in metabolism and diet.