Each person needs a different amount of energy depending on factors such as:
If you look on the side of food packets you will see the food's energy content. This is usually measured in kilojoules, kJ. For example, a one-year-old baby needs 3850 kJ each day to continue to grow, whereas an adult Olympic swimmer in training needs 15,600 kJ each day. Someone who sits at a desk all day will need less food than their twin who climbs ladders all day to wash windows.
If the amount of energy you get from your food is different from the amount of energy you need, your diet will be imbalanced:
For a given height, there is a range of body weight that is thought to be healthy.
Starvation happens if you eat so little food that your body becomes very underweight. This can eventually cause death. Obesity happens when you eat so much food that your body becomes very overweight. This can also cause death, for example through an increased chance of heart disease.
The average man needs about 10,470 kJ per day, and the average woman needs about 8370 kJ per day. Food labels show how much energy the food provides. The table shows three examples:
|Baked beans||1395 kJ per can|
|Bread||364 kJ per slice|
|Grated cheese||17.45 kJ per g|
Using these numbers, the daily energy needs for a woman could be met from 6 cans of baked beans (8370 ÷ 1395 = 6) or from 23 slices of bread (8370 ÷ 364 = 23). The daily energy needs for a man could be met from 600 g of cheese (10470 ÷ 17.45 = 600).
However, we need to eat a mixture of different foods in the correct proportions to achieve a balanced diet. The amount we need to eat will vary from person to person.