A 'balanced' diet is one which contains both the right quantity and the right types of food. The quantity of food is important because the right amount ensures that you remain in the ideal weight range for your height and so avoid the health risks associated with being very much over or under weight. How much you need depends on your build, your sex, how active you are and your metabolic rate (how fast you burn up energy). The right types of food are important because the body needs a wide range of nutrients in varying amounts in order to function healthily. Avoiding foods which are rich in some or all of the nutrients the body needs and filling up on those which lack nutritive value is hazardous to health. Knowing what foods contain which nutrients, why they are needed and just how much is needed will help you plan a balanced diet.

* Carbohydrate in foods may be found in one or more of the following forms: sugars, starches and fibre.

* Starch is a good source of carbohydrate energy. Bread, potatoes, rice, pasta and cereals are all rich in starch.

* Carbohydrates are used by the body as a source of energy and can be stored as glycogen (or 'animal starch') in the liver and muscles, for later use; excesses are converted to fat and stored around body organs and under the skin.

* Table sugar (sucrose) provides energy but no nutrients and is therefore unnecessary in a healthy diet: just as much energy can be obtained from natural sugars in fruits and young vegetables.

* Fibre is only partially digested by humans so provides little energy, but it does play an important part in the emptying of the large bowel, among other vital functions. Good sources are wholemeal bread and pasta, brown rice, vegetables and fruit.

* Starch and fibre containing foods should account for about 60 per cent of a healthy diet.

* Proteins are the substances from which our bodies build tissue for growth and repair. Their chemical composition is of chains of amino acids. Foods such as eggs, meat, fish, milk and cheese contain all the necessary amino acids; vegetable sources contain 'incomplete' chains but in certain combinations can provide the correct balance.

* Protein should account for about 10 per cent of a healthy diet.

* Fats contain essential fatty acids which keep the body functions working. They carry the fat-soluble vitamins A, D, E and K. Fats are very concentrated Calorie sources and make food more palatable.

* Fats should account for about 30 per cent of a healthy diet; many Western diets contain up 45 per cent fats.

* Saturated fats are mainly of animal origin: meat, milk, butter and cheese are high in saturated fats, as are cocoa and coconut oils. Saturated fats in the diet have been shown to raise blood cholesterol to dangerous levels. Foods containing a high percentage of saturated fats should only be taken in moderation.

* Polyunsaturated fats tend to occur in the highest levels in plants: safflower, sunflower, corn and soya oils are rich sources, as well as fish. They tend to lower blood cholesterol levels and are therefore thought to be a good substitute for saturated fats.

* Monounsaturated fats, which occur in olive oil, nut oils, nuts and avocado pears, for example, appear to have still greater cholesterol-lowering properties than polyunsaturates.

* Alcohol and foods high in fat and sugar should be avoided, and at best regarded as special occasion treats, certainly not as everyday necessities. Cut down on them and fill the gap, if there is one, with starch.