Why proteins are important ?
The "genes' in our cells which give us heredity, dictate the colour of our hair, or its future disappearance, are probably protein molecules. "Muscles, nails, skin, hair, tissues " are largely of protein composition. Even your teeth contain minute protein.
The "hemoglobin" molecule that makes your blood red is mostly protein. The "haemo" or iron-containing fraction is a five percent, and the protein or "globin" fraction is 95 percent. Many cases of simple anemia do not respond to iron tablets alone, if underlying protein deficiencies also exist. This explains one way in which stepped up protein intake may restore zest and vigour to some people who complain of chronic fatigue.
Many 'hormones' are proteins or are intricately assembled from protein elements.
"Enzymes", those wonderful spark plugs of every single chemical process we live by are proteins.
Wear and tear of tissues requires protein repair. Children, of course require more protein than adults (babies, three or four times more, relatively) because they are growing and building " new" tissues. But adults need constantly renewed supplies of protein too. Studies with radioactive tracer substances prove beyond doubt that protein of living tissues are being exchanged and this process never ceases for an instant while life remains. Twice a year there is a complete turn over of proteins in your body for new ones. Your liver exchanges its protein in about 10 days.
Adequate protein helps to keep the water balance of your body at normal levels. Many people aren't really fat. They are water-logged. Their tissues hold fluids in such abnormal amounts that when a finger is pressed into their flesh, a pit like depression remains for some time. When placed on well-balanced diets the torpidity vanishes and bodies become normally slender as their nutrition improves. The water retention from which these people suffer is called oedema, and this particular type, caused by inadequate diet is called "nutritional oedema" or "hunger oedema".
Since 70 percent of your weight is represented by water in one from or another, you can see what a difference protein can make to your weight. There are of course, other factors involved in oedema - it isn't that the protein always does the job single - handedly, but that other factors can't operate if protein is deficient.
You get your proteins from foods, of course. But - foods vary both in quantity and quality of protein they contain. The differences have to do with little things called amino-acids.

What are proteins made up of
All proteins are built out of various combinations of 23 different kinds of "chemical units". These units or building blocks are nitrogen containing substances known as amino acids. Billions upon billion different combinations can be made by re-arranging, adding or subtracting, changing the sequence of these 23 structural units.
The proteins you obtain from food are broken down by digestion into the amino acids building blocks that composed them. The chemical precision of your body, selects amino-acid 'bricks' and builds them into hundreds of unique proteins upon which life processes are utterly dependent.
Although 23 amino-acids are known, not all of them have to be obtained regularly from food. But eight amino-acids are rated indispensable. We must regularly obtain these eight from food, and they must be available in the body, when they are needed , if we want to stay healthy. Any one of these eight is essential to good health hence these eight are also called essential amino acids. It has been proved that experimental animals sicken and die if deprived of just one of these "essential eight" aminos. A hormone, an enzyme, a protein necessary for some mysterious body process, can't be made because an essential amino acid is not at hand at the right time.
So just eating a generous 'quantity' of protein isn't enough. 'Quality' must be there too for buoyant health.

How to judge the protein quality ?
Certain foods furnish proteins that are rated by nutritionists as "biologically complete " . "They are" sometimes simply called complete proteins. This simple means that they furnish all eight of the essential amino acids, all at once, and in good quantity. A simple, easy-to-remember way of judging protein quality is to think of foods as failing into 4 general classes :

Class I : Meat, poultry, fish, egg, milk and milk products, cottage cheese.

Class II : Beans, peas and pulses. "Soya Bean" is an exception, in that, when cooked properly, it supplies fairly liberal amounts of complete protein equal to Class I proteins.

Class III : Cereals.

Class IV : Vegetables and fruits.

Class -I foods are best for protein, for they furnish all eight essential amino acids ( and others too) at one dose, so to speak. They promise complete proteins. They do not necessarily provide every essential amino acid in ideal amounts, but there's at least a little of each one, adding, upto top quality.
It is neither necessary nor desirable (nor very thrifty either) to live wholly on Class -I foods. You can make Class 2-3 and 4 foods furnish complete protein by eating a little of Class I food along with them. Biologists call it " Supplementation". Any essential amino acids that may be missing are furnished by Class -I food, and the value of the total protein intake is greatly enhanced. Your meal then provides all at once-and that is known to be tremendously important -all necessary amino-acids, so your body has all the ingredients it needs at the moment to assemble the hundreds of different proteins necessary for health.
A splendid dietary principle is 'to eat at least one biologically complete protein at every meal." This is automatically done if you consume at least a small portion of some Class-I food every time you eat anything at all.
There are times, of course, when Class-I foods will be skipped from necessity or choice.
Then, a wonderful way of improving protein quality is to serve a number of different class -2, 3 and 4 foods simultaneously. Include them in your meals. Let sprouted pulses and beans, vegetables and cereals supplement each others amino acids. That way, an essential amino acid lacking in wheat may come from a potato.
If all this discussion about proteins seems too complicated to bother your head about, then just remember simple rule of healthful eating. Good nutrition is furthered by eating a wide variety of foods, so that the deficiencies of one are made up by virtues of another.

How useful are proteins in fat-loss programmes?
People on a fat-loss programme, like everybody else, need enough protein, vitamins and minerals to nourish vital tissues and enter into chemical combinations that keep tissues alive. You could lose weight on a diet which does not supply enough protein to the body. Then as discussed in earlier chapter, your body will draw energy from your muscles, your liver and other organs etc., scientifically called negative nitrogen balance.
Adequate protein of safe and sound fat reducing diets prevents such a disaster. Your vital tissues will be protected. You will not be weakened physically. A diet that supplies sufficient protein ensures that " any loss of weight it brings about is caused by loss of fat and nothing else."
Moreover, protein has appetite -satisfying qualities. Protein in a reducing diet helps to allay hunger pangs or appetite pangs.
Another big advantage for reducers is that generally speaking, protein slims you 'faster' than anything else.
When food enters your body it stimulates the existing metabolic rate to help us digest and metabolize what we eat. This action of food is called " Specific Dynamic Action." Doctors, call it SDA. Protein is superior to fat and carbohydrate in this respect. Protein has a high specific dynamic action. It fans body fires to a clean, hot flame or in other words boosts the metabolic rate of the body. This helps to keep human energies at a high level. It also compels us to burn or oxidize fat more than we otherwise would.
So a safe and sound reducing diet furnishes adequate protein for three important reasons :

1. It protects vital tissues from starvation.
2. It is hunger-satisfying.
3. It speeds up the slimming process somewhat.

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