1Energy from food
Food gives you energy, measured in kilojoules (kJ). Your body uses it all the time: to keep your heart beating, keep you warm, move and grow, even while you sleep.
kilojoules (kJ)
Lesson 4.2 notes
Energy and a balanced diet
Food energy is measured in kilojoules. Work out the energy in a day's food, see who needs more, and find out what happens when a diet is unbalanced.
2Energy on the label
Food labels give the energy in 100 g. A 30 g portion has 30/100 of it, so 1600 kJ per 100 g gives 1600 × 0.3 = 480 kJ.
3Who needs more?
How much energy you need depends on your age, your size, whether you're still growing and how active you are. A 14-year-old needs more than a 7-year-old.
growingactive
4A day's energy
Add up the energy in everything eaten in a day and compare it with the energy needed. These meals and snacks add up to 9800 kJ: about right for a 14-year-old girl.
5Energy in, energy out
Take in more energy than you use and the extra is stored as fat. Take in less and the body uses up its stores. When they balance, neither happens.
fat
6Too much or too little
Taking in much more energy than you use for a long time can lead to obesity, raising the risk of heart disease and type 2 diabetes. Far too little food leads to starvation.
obesitystarvation
7Deficiency diseases
Too little of one vitamin or mineral causes a deficiency disease. Too little vitamin C causes scurvy, too little vitamin D or calcium causes rickets, and too little iron causes anaemia.
deficiency diseasescurvyricketsanaemia
Explore: Energy balance lab
Pick a person and how active they are, then plan their meals for a day. Compare the energy in their food with the energy they use.
Common mistake: A balanced diet is about more than energy
Two foods can give the same energy but very different nutrients. A balanced diet needs enough of every nutrient, not just the right number of kilojoules.
Remember
- Energy in food is measured in kilojoules (kJ). Labels give the energy in 100 g and in a portion.
- How much energy you need depends on your age, your size, whether you're growing and how active you are.
- Much more energy than you use, for a long time, can lead to obesity. Far too little leads to starvation. Too little of a vitamin or mineral causes a deficiency disease.
Going further at GCSE