Food and Fuel:
Human beings need food for a variety of reasons. Food builds, nourishes and maintains the human body and gives energy. In other words, food is needed to supply fuel to the body and to provide material for its growth and repair. Some foods can serve only one purpose, some for all three.
There is a scientific principle behind the process of energy provided by food. Food gives energy to man as fuel gives energy to a machine. In order to produce work or heat, a man needs fuel, like a steam engine. Food is the fuel of the human body. The amount of heat he produces is just the same as the amount which he would get if his food were burned when allowance has been made for wastage. In a more accurate way, the observed and calculated heat production in a good experiment agree to within one part in two hundred. This amount to say that man is a machine fed by the fuel of food. Human machinery cannot work without food. If the food provided to the human-machine is inadequate or deficient, the efficiency of human work will greatly suffer even as the efficiency of a petrol engine will suffer if the petrol provided by scanty or impure. The energy developed from the union of food eaten and the oxygen breathed is converted directly in muscular work.
What are the steps by which food is changed into energy? First, the food we eat has to be digested, so that the body can work with them. This is done with the help of the digestive juices which mix with our food as we chew and swallow it. The food is then changed into sugar energy which passes through the body walls into the bloodstream from where it is carried to different parts of the body. Our muscles do work by using up this sugar, by making it combine with the oxygen we breathe. This oxygen comes from our lungs when we take in air and is absorbed in the blood. The blood then carries the fresh oxygen to all parts of the body. At the same time, it picks up carbon dioxide and waste gases from our body tissues. These waste gases are deposited in our lungs and expelled when we breathe out.
The chemical substances which can be used as fuel fall into three groups: carbohydrates, proteins and fats. Carbohydrates are mainly found in starch and sugar. Starch and comes mainly from potatoes and cereals. Proteins supply as much energy as carbohydrates. They are to be found in great amounts in cheese and milk. Fats roughly provide twice as much energy as proteins and carbohydrates. They are, therefore, a more concentrated form of energy foods. They are chemically much like sugar and starch but have less oxygen than carbohydrates.
The harder we work, the more fuel we burn and the more oxygen we need. The fuel value of food is measured in units called calories. An average man doing light work requires nearly 2500 calories of heat per day. Those doing heavy work may require over twice as much. In wealthy and advanced countries, people get sufficient fuel value in their daily diet though many do not get it in the most digestible form, nor do they get food that is adequate from other points of view. It has been discovered that besides the fuel foods to supply energy, proteins for growth and repair at least wight other kinds of chemical substances which he cannot make in his own body.
Therefore, a balanced diet or good food must contain all the chemicals and elements necessary for human growth and energy. The most important solid constituents of our bodies are called proteins. The best proteins are of animal origin, since milk are just as good as meat proteins, there is no physiological objection to a vegetarian diet supplemented by enough milk or cheese.
