Energy

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Food provides us with energy, like petrol provides cars with fuel to run or like coal used in power stations to generate electricity to operate a factory. We use up energy in whatever activities we do. Physical work, such as walking, running and exercising, requires energy. Even resting and mental work, such as thinking, requires energy! Energy is also used in such basic body processes as the heart beat and digestion in the stomach.

Measurement of Energy

Energy is measured in joules or calories. Both units are very small. So when talking about the energy value of food and the energy output of body activities, we multiply the values by one thousand (kilo=1000) and refer to them as kilojoules or kilocalories. Kilocalorie is often abbreviated to Calorie spelled with a capital C. (A kilocalorie is defined as the heat energy needed to raise the temperature of 1 kilogram of water from 14.5° to 15.5° C (58.1° to 59.9° F).) We usually use a Calorimeter to measure the energy content of food substances.

For conversions,

• 1 kJ = 0.24 Cal
• 1 Cal = 4.2 kJ

Energy is found in carbohydrates, fats and proteins. Carbohydrates are the most abundant foods in the world, and fats are the most concentrated and easily stored fuel. If the body exhausts its available carbohydrates and fats, it can use proteins directly from the diet or break down its own protein tissue to make fuel.

Average values of energy-yielding constituents

• One gram carbohydrates = 3.75 Calories (16 kJ)
• One gram proteins = 4 Calories (17 kJ)
• One gram fat = 9 Calories (37 kJ)
• One gram alcohol = 7 Calories (29 kJ)