THE word protein comes from the Greek word "protos" which means first. In olden times, humans have always preferred meat products from animals they capture from their numerous hunting activities with the firm belief that it provides them with all the energy and strength to run after injured prey and to carry them home after the hunt.
They were right, indeed. While it is true that one gram of protein, like carbohydrates, yield 4 kilocalories for energy purposes, proteins are not primarily meant as energy-giving food- which is the domain of carbohydrates and fats. What makes the body stand and have bulk, are all derived from proteins. The skeleton which makes the body stand, and the muscles that attach to it, the ligaments and tendons and cartilages as well as the tendons that connect different organs in the body are all sourced from proteins. That glossy lustrous hair, the pearly teeth, strong nails are all protein-derived. Thus, it is only under extreme conditions like prolonged starvation or food deprivation, as what would happen if a person is trapped, but not hurt by a big boulder of concrete from a strong earthquake; by then what keeps him alive would first be glycogen, the stored carbohydrates in his liver and skeletal muscles, then all that fat in his body and only when these two are consumed and gone will the body utilize protein as a source of energy.
Actually, the physical structure of the human body - hair, nail, bone, muscle etc. - are made of amino acids which are the building blocks of proteins. From a nutritional point of view, in order to have maximal, optimum protein metabolism, a person should have one gram protein per kilogram weight, so a 70 kg man should have 70 grams proteins. There is also the concept of essential also called indispensable amino acids- because they are not produced by the body and therefore must be provided for in the diet, whereas the non-essential can easily be produced by the body, hence they are also called dispensable.
The richest source of proteins is eggs, the fresher the better meaning, once the hen has brought is out and consumed right away, would provide nutritious essential- but not all- amino acids. Take note, we are not encouraging raw eggs because Salmonella typhosa of typhoid fever, might be inside. Moreover, raw egg white contains the substance avidin, which destroys the important vitamin, biotin. Fishes, whether fresh water or saltwater - are also excellent sources, remember the omega 3 fatty acids from deep sea fishes. Meats of course, are on our short list, although from cancer specialist, there is the warning to limit, not totally avoid naman, red meats- beef, veal, venison, lamb- because of their supposed involvement in colon cancer, especially when grilled. White meat like pork and of course, the favorite of kids, chicken. Among the veggies and fruits, legumes like beans are also rich sources of proteins with soya being the most prominent especially for vegans. Biochemistry and nutrition experts all agree that with fats, vegetable oil is healthier than fats derived from animals but when it comes to proteins, animal proteins are superior in so far as providing the essential amino acids needed for optimum sound nutrition and healthy well being.