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Energy
What is Energy?
Energy cannot be created or destroyed. It is transformed from one form to another. Plants transfer sunlight energy into chemical energy by a process called photosynthesis.
We get our energy from plants, animals which have eaten plants (herbivores), animals which eat the herbivores (carnivores) or other carnivores.
In our bodies, the chemical energy in food is transferred to movement, sound and heat energy.
Most of our energy is supplied by the chemical energy stored in carbohydrates, fats and proteins.
A pie chart to show where our energy should come from.
How much energy is there in 1 gram (g) of carbohydrates, fats and proteins?
- Carbohydrates give us 3.75 kcal per gram
- Fats contain the most energy as each gram gives 9 kcal
- Proteins give us 4 kcal per gram
What is Energy measured in ?
Energy is measured in Calories (cal) or in Joules (j). Because the energy in food is so large we usually talk about kilojoules and kilocalories.
- A kilocalorie (kcal) = 1000 calories
- A kilojoule (kJ) = 1000 Joules.
- A megaJoule (MJ) = 1000 kJ .
- 4.18 kJ = 1 kcal
Everyone is different !
A healthy diet should supply the correct amount of energy. As everyone is an individual, their energy requirements will differ depending upon their age, body size, sex, state of health, activity level and genetics.
How much Energy do you need ?
There are Recommended Daily Amounts for energy as well as nutrients. A girl aged between 11 and 14 should have 1850 kcal (7720 kJ) a day and a boy of the same age should have 2220 kcal (9270 kJ) per day. A girl between 15 and 18 should have 2102 kcal (8830 kJ) per day and a boy of the same age group should have 2750 kcal (11510 kJ) per day.
What foods should our Energy come from ?
55% should come from carbohydrates, 30% from fats and 15% from proteins