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what is a calorie
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A calorie is a unit of energy.
- In physics/chemistry a "small calorie" (written cal) is the amount of energy required to raise the temperature of 1 gram of water by 1 °C. By definition 1 cal = 4.184 joules (J).
- In nutrition the term "Calorie" (capital C) nearly always means a kilocalorie: 1 Calorie = 1 kilocalorie (kcal) = 1000 small calories = 4184 J. Food labels that say "200 Calories" mean 200 kcal.
- Why it matters: calorie counts for food come from measuring the energy released when food is burned (bomb calorimetry) but the usable energy your body gets differs due to digestion, absorption, and metabolic losses.
- Typical energy densities: fat ≈ 9 kcal/g, carbohydrate ≈ 4 kcal/g, protein ≈ 4 kcal/g, alcohol ≈ 7 kcal/g.
In modern science the joule (J) is the SI unit of energy; calories are still commonly used in nutrition and everyday contexts.
- In physics/chemistry a "small calorie" (written cal) is the amount of energy required to raise the temperature of 1 gram of water by 1 °C. By definition 1 cal = 4.184 joules (J).
- In nutrition the term "Calorie" (capital C) nearly always means a kilocalorie: 1 Calorie = 1 kilocalorie (kcal) = 1000 small calories = 4184 J. Food labels that say "200 Calories" mean 200 kcal.
- Why it matters: calorie counts for food come from measuring the energy released when food is burned (bomb calorimetry) but the usable energy your body gets differs due to digestion, absorption, and metabolic losses.
- Typical energy densities: fat ≈ 9 kcal/g, carbohydrate ≈ 4 kcal/g, protein ≈ 4 kcal/g, alcohol ≈ 7 kcal/g.
In modern science the joule (J) is the SI unit of energy; calories are still commonly used in nutrition and everyday contexts.
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