Primitive Man believed that the strength and courage of animals could be assumed by eating their flesh. Today we know that a well balanced diet is essential to health and that various foods provide us with energy and new tissue needed for growth and repair of our bodies.
Nutrients required by the body are water, proteins, fats, carbohydrates, mineral salts and vitamins. Proteins and minerals are vital for the growth and repair of the body while fats and carbohydrates provide energy and vitamins regulate the chemical reactions of the tissues.
All are necessary and combine to keep the body in good health but the most essential of all is water. This substance makes up over two thirds of all living matter and it is the medium in which all cellular reactions occur. Without water life as we know it could not exist. Some more obvious functions which take place because of the presence of water include blood circulation, nutrient transfer, excretion and temperature control.
Protein deficiency is a major health problem in many parts of Asia, India, Africa, Central and South America. Young children are the worst affected and may be retarded in growth, listless and tired, with distended stomachs and bare patches on the scalp. The only cure is large amounts of high-quality protein.
Diseases may also be caused by lack of vitamins in the diet. One such disease is scurvy which was once common amongst sailors who existed for long periods without fresh fruit and vegetables and therefore suffered from a lack of vitamin C. However, too many vitamins may also cause problems. Large quantities of vitamin A taken over a long period of time are known to damage the liver, bones and skin, while too much vitamin D can cause vomiting, headaches and diarrhoea.
Proteins and Carbohydrates
An excess of carbohydrates and fats may lead to overweight, high blood pressure and heart disease. It can therefore be seen that the key to good health lies in the satisfactory balance of intake of vital nutrients.
The primary tissue-building substances are proteins, which are made up of a combination of nitrogen-rich amino acids. Proteins aid the development of muscle, bone, cartilage and skin as well as furnishing antibodies which circulate in the bloodstream to fight bacteria. Proteins are found in such foods as meat, milk, cheese, eggs, cereals, peas, beans and nuts. Carbohydrates are found in the form of sucrose, lactose and starches and are present in such foods as fruits, vegetables and cereals.
They are also supplied in processed foods like bread, cake, spaghetti, ice cream, soft drinks and sweets. Fats, or lipids, provide more energy than carbohydrates and are particularly useful because they can be stored in the body as reserves of energy.
They are found in milk, cheese, eggs, oils, fish, nuts and meat.
One of the body's most important minerals is calcium, which is essential for blood-clotting, the muscular actions and the formation of bones and teeth. The main sources of calcium are milk and manufactured dairy products. Lack of calcium may result in soft, chalky bones and teeth. Iron is essential for the formation of red corpuscles in the blood and may be supplied by vegetables, meat, fish, poultry and cereals.
Other important minerals are phosphorus, sodium potassium, iodine, chlorine and magnesium. These are provided in water, salt, fruit, vegetables, meat and cereals.
Vitamins and Calories
Vitamins are organic compounds present in all fresh foods and responsible for speeding up the various chemical reactions in the body's tissues. There are six main vitamins (A, B, C, D, E and K) and many subdivisions of these. Vitamins are essential for blood clotting, nerve function, bone growth and good vision.
The unit of energy given out by any particular food is known as a kilojoule. According to our age, weight and daily activities we need varying amounts of kilojoules to supply our energy requirements. For instance, a laborer performing heavy manual work needs considerably more kilojoules than a clerk sitting at a desk all day. Every single movement from the blinking of an eyelid to the racing of our legs as we chase a ball burns up kilojoules.
If we take in more kilojoules than we use, our weight will increase but if we use more than our intake, our bodies draw on the energy reserves stored in our fat and so our weight decreases. People wishing to control their weight usually restrict their kilojoule intake and increase their physical activities. For various reasons of health and nutrition it is often necessary to undertake a restricted diet. This should only be done under instructions from a doctor or qualified dietitian.