The food and drink that we eat is called our diet. Food is made up of a range of chemicals, the chemicals in food that our bodies uses are called nutrients. Different nutrients do different jobs in the body. To stay healthy, our diet must be balanced. This means that it contains all the essential nutrients in the correct amounts. Nutrients are classified into five main groups, proteins, carbohydrates, fats, vitamins and minerals. One particular carbohydrate called dietary fibre is often included as a separate nutrient, as is water, making seven types altogether.

Proteins

The main job of protein is to build new body tissue for growth and repair. It is also used to make important chemicals such as enzymes and hormones. Protein in food is not used in the form it is eaten but is broken down during digestion into amino acids. These amino acids are then rebuilt into useful proteins by our body. Foods that supply protein include meat, fish, milk, eggs and poultry. Plant sources are peas, beans and cereals. If the body exhausts its available carbohydrate and fat, then protein from the diet or body tissue can be used as a source of energy. The recommended protein intake per day is 55g for men and 45g for women. People in the UK are unlikely to suffer from a deficiency of protein. Protein deficiency results in a form of malnutrition called marasmus. This results in the loss of body fat and the wasting of muscle.

Minerals and Vitamins

Minerals and vitamins are called micro-nutrients as they are needed in much smaller quantities than the other nutrients. A lack of any particular mineral or vitamin leads to an associated deficiency disease. Minerals are inorganic chemicals that play an important part in such processes as the action of enzymes.

Vitamins are organic compounds that mainly help with the breakdown and use of food in the body. Some vitamins also help with the formation of cells and hormones. Vitamins are classified into two groups – fat soluble, such as vitamins A and D, and water soluble, such as vitamin C and the vitamin B complex. Water-soluble vitamins cannot be stored and need to be replaced each day.

Carbohydrates

Carbohydrates provide most of the energy in human diets. There are two main kinds of carbohydrate: starchy carbohydrates found in bread, pasta, rice, cereals, and sugars such as sucrose and fruit sugars. It is currently recommended that we get 50% of our energy from carbohydrates, of which 40% should be starchy carbohydrates. Starchy carbohydrates provide bulk to our diet and can also contain additional nutrients such as protein, vitamins and minerals. Sugars are less beneficial, particularly refined sugar. This is high in energy, bad for teeth and contains no other nutrients.

Fibre

Some carbohydrate that comes from plant cell walls cannot be digested by humans. This forms an important part of the diet and is called dietary fibre. A diet lacking fibre can lead to constipation and the development of high pressure in the digestive tract; this has been linked with a variety of diseases of the colon such as hiatus hernia. Fibre lowers cholesterol, reducing the risk of heart disease. Fibre also binds to a number of chemicals that cause cancer, and so can provide some protection against cancer of the intestine. Dietary fibre is often referred to as NSP, which stands for non-starch polysaccharide. There are two forms of NSP – soluble and insoluble. In general, people in the UK have about a third too little dietary fibre in their diets and should eat more whole grain foods, fruit and vegetables.

Fats

Per gram, fats provide just over twice as much energy as carbohydrates and proteins. Fat is stored in the body for use when no carbohydrate is available. There are two main types – saturated fats, which are usually solids and come from animal sources, and polyunsaturated fats, found mostly in seed oils, these are liquids at room temperature. Excess intake of fats has become a serious health concern and saturated fats in particular have been found to raise blood cholesterol contributing to the risk of heart disease. Current government advice recommends reducing the amount of fat in the diet, particularly saturated fats.

The Balance of Good Health

In 1994 the government produced a set of eight guidelines for a healthy diet called ‘The Balance of Good Health’. Even if you know the exact nutritional content of your food, it is very difficult to try to eat precisely the recommended daily amounts. Their solution was to get people to think in terms of food groups rather than nutrients, and then provide a simple rule of thumb for eating the right proportion of these food groups. The key was to achieve a balance over one or two weeks, not necessarily every meal.