What Is a Calorie?
A calorie (from Latin calor, meaning “heat”) measures energy. In nutrition, calories quantify the energy we get from the three macronutrients—protein, carbohydrates, and fats. Technically, a kilocalorie (kcal) is the energy needed to raise 1 kg of water by 1 °C.
Why Calories Matter
Weight changes when energy in (calories eaten) differs from energy out (calories burned). To lose weight, most adults aim for about 1,400–1,800 kcal/day, balanced roughly as:
- 30–40% carbohydrates
- 30–35% protein
- 30–40% fat
Including plenty of fruits and vegetables boosts essential vitamins and minerals.
Key Factors in Calorie Needs
- Age: Younger adults generally need more energy. For example, an 18-year-old may require ~2,000 kcal/day, whereas an 80-year-old may need ~1,200 kcal/day.
- Gender: Men often require more calories than women—around 2,500 kcal/day versus 1,500 kcal/day—due to higher average muscle mass and size.
Understanding these factors helps you tailor your daily intake for health and weight goals.