What is food energy?

  • Food stores energy, which when eaten is transferred to the consumer.

  • Each individual requires a specific amount of food, depending on their energy requirements.

  • Sports nutritionists advise athletes to choose foods that will help them perform at their best.

Learn about food energy from a sports nutritionist

What is food energy?

Food stores energy. Eating transfers the stored energy from the food to the animal that eats it. The energy keeps the animal alive, and allows it to carry out its activities.

How much do you need?

Energy is measured in joules (J) or kilojoules (kJ). One kilojoule is the same as 1000 joules. An older unit for measuring food energy is the kilocalorie, often just called calories. One calorie is 4.2 J.

Different animals need different amounts of energy. For example, an elephant needs around 200,000 kJ daily, and a cat about 800 kJ.

The amount of energy a human needs depends on many things, including their age and what they are doing. Typically, a 13-year old girl needs 9,000 kJ/day and a 13-year old boy around 10,000 kJ/day.

How much energy is stored in foods?

Different food groups store different amounts of energy. For example:

  • 100 g of carbohydrate stores around 500 kJ
  • 100 g of protein also stores around 500 kJ
  • 100 g of fat stores around 3000 kJ

Nutrition labels found on packaged foods are calculated by food companies. Scientists at the company find out the mass of carbohydrate, protein and fat in 100 g of the food. Using the values listed above they then calculate the energy values.

How can knowledge about food energy help us?

Everyone needs some knowledge of food energy, so that they can eat sensible amounts of the foods they need to stay healthy.

Sports nutritionists guide athletes in deciding what to eat to perform at their best. They need a good knowledge of how much energy is stored in different foods, as well as how quickly the energy is released to the body.

Food energy quiz

Test your knowledge of food energy with this quick quiz.

Where next?

Discover more about this topic from around Bitesize.

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What are carbohydrates?
What is digestion?