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To convert kilocalories to joules, multiply by 4,184. So 1 kcal = 4,184 J, 100 kcal = 418,400 J, and 2,000 kcal (typical daily diet) = 8,368,000 J = 8.37 MJ. The kilocalorie (kcal) is identical to the food "Calorie" printed on nutrition labels.
Nutritional science and physics use different energy units for the same physical quantity. A 500 kcal meal contains 2,092,000 J — enough energy, if converted entirely to mechanical work, to lift a 70 kg person about 3,046 meters. The human body converts food energy with roughly 20–25% efficiency for physical activity.
Did you know? The EU requires food labels to list energy in both kilojoules (kJ) and kilocalories (kcal). A label reading "835 kJ / 200 kcal" confirms the conversion: 200 × 4.184 = 836.8 kJ. The slight difference from 835 kJ is due to rounding on the label.
Nutrition scientists publishing research in international journals use joules (or kilojoules) as the SI standard. Exercise physiology studies express energy expenditure in both kcal (for practitioners) and kJ or MJ (for scientific analysis). Comparing metabolic energy with electrical energy requires converting kcal to joules.