What is a balanced diet?
A balanced diet is a diet that contains all the classes of food in the correct amounts and proportions to keep the body healthy. There are seven classes of food: carbohydrates, proteins, fats, vitamins, minerals, water and fibre. Each has its own job — carbohydrates and fats supply energy, proteins build and repair the body, and vitamins and minerals keep body processes working smoothly. Fibre adds bulk that helps digestion, and water is needed for almost every process in the body. A meal made up of only one type of food, however tasty, is never balanced, and the correct proportions differ from person to person.
Calorific value
The calorific value of a food is the amount of energy released when 1 gram of the food is completely burnt. It is measured in kilojoules per gram (kJ/g) using a calorimeter. Different foods release different amounts of energy.
| Food class | Approx. calorific value (kJ/g) |
|---|---|
| Carbohydrate | 17 |
| Protein | 17 |
| Fat | 38 |
Key idea
Gram for gram, fat releases more than twice the energy of carbohydrate or protein. That is why fatty and oily foods are described as being high in energy.
How much energy do we need?
Daily energy needs are not the same for everyone. They depend on age, sex, body size, level of physical activity and special states such as pregnancy. A rubber tapper or a construction worker uses far more energy than an office clerk of the same age.
Example
If a teenager regularly eats more energy in food than the body uses, the extra energy is stored as fat and can lead to obesity. If intake is far too low, the person becomes underweight and lacks energy. Balancing intake and output keeps body mass healthy.