Over ten per cent of your body tissue is made of protein so you need to eat protein to renew it and, if you are growing, the more you need. Protein is built up of chemical units called amino acids. These are then rebuilt in your cells to form the proteins you need. Good sources of protein are lean meat, fish, cheese, eggs, milk, nuts and beans.
These are built up of different sugars (including glucose) and give you most of your energy. You can either eat the sugars directly in foods, such as fruit and jam, or in the form of starch in foods, such as potatoes, rice and bread.
Starch becomes sugar inside your body. If you eat more carbohydrates than you need, the excess is converted into a substance called glycogen and stored in your liver and muscles. Or it is converted into fat. It is best to avoid eating sugar in drinks and in food, such as cakes, biscuits, sweets, chocolates and convenience foods. Besides turning to fat, it is bad for your teeth.
Like carbohydrates, fats provide you with energy. They also form parts of your cells, such as the membranes. Fat is stored in your body and helps to keep you warm. The fats you eat can come either from animals, in foods such as meat, milk, butter and cheese or from plants, in food such as vegetables oils and nuts. Too much fat, especially animal fat, may play a part in heart disease.
These are involved in vital chemical processes in your body. You need small amounts of about 20 different minerals. Calcium and phosphorous found in foods, such as milk and cheese, help to make your bones and teeth strong.
Iron is needed by your red blood cells and is found in foods such as liver and green vegetables. A lack of zinc, which is found in nuts and fish, may cause skin rashes. You also need sodium chloride (salt). In general, people in developed countries eat more salt than is necessary and this may be associated with high blood pressure.
Fiber, or “roughage,” consists mainly of cellulose which is a type of carbohydrate your body cannot digest. It is found in vegetables, fruit and whole meal bread. Fiber is valuable because it is bulky and this helps to make the muscles of your intestines (bowels) work efficiently and so prevents constipation. Fiber may help to prevent serious diseases of the intestines, including cancer.
You are losing water all the time in your urine, in your sweat and when you breathe out, so you have to take in water to replace it. There is water not only in drinks but also in solid foods. Lettuce, for example, is nine-tenths water. You could stay alive longer without food than you could without water.
You need small amounts of about 15 different vitamins so that essential chemical processes can take place in your body. A lack of any particular vitamin causes a specific illness. For example, if children do not have enough vitamin D they get an illness called rickets which stops their bones developing properly. Different kinds of vitamins, their sources, and what they are necessary for, follows:
- Vitamin A – milk, butter, eggs, fish oils, fresh green vegetables. Necessary for eyes (specially seeing in the dark), skin.
- Vitamin B – whole meal bread, rice, yeast, liver, soya beans. For energy production in all your cells, nerves, skin.
- Vitamin C – oranges, lemons, blackcurrants, tomatoes, potatoes, fresh green vegetables. For blood vessels, gums, healing wounds, possibly preventing colds.
- Vitamin D – fish oils, milk, eggs, butter (and sunlight). For bones and teeth.
- Vitamin E – vegetable oils, whole meal bread, rice, eggs, butter, fresh green vegetables. Uses not yet understood.
- Vitamin K – fresh green vegetables, liver. For clotting blood.
If you habitually overeat, the excess food is converted into fat and stored in special fat cells. The cells can increase in size and so you put on weight and “get fat.” If you eat less than you need, your stores of fat are used up as energy and you get thinner. On average, fat people die younger than thin people. They are more likely to suffer from certain illnesses, including heart disease!