protein

After water, protein is most plentiful component in our body. Every cell in the human body contains protein. It is a major part of the skin, muscles, organs, and glands. The human body contains between 30000 and 50000 unique proteins. Proteins are made up of smaller units called amino acids, compounds containing carbon, hydrogen, oxygen, nitrogen and in some cases sulphur. A typical protein may contain 500 or more amino acids. Each protein has it's own unique number and sequence of amino acids which determines it's particular structure and function.

Essential Amino Acids

Human body can manufacture most of the amino acids required for making protein. However, body cannot manufacture all amino acids required by humans. Eight amino acids must be supplied in the diet.
Essential amino acids are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
During growth, arginine and histidine are also considered to be essential amino acids.

Protein in Food

A complete protein source is one that provides all essential amino acids in adequate amount. Complete protein examples are animal foods, such as meat, fish, poultry, eggs, milk, and milk products.
Plant foods, especially grains and legumes, often lack one or more of the essential amino acids, but when they are combined, become complete protein sources. For example, combining grains with legumes result in complete protein source.

Animal Protein vs. Plant Protein

It is difficult to separate the effects of animal protein from the effects of animal fats because they are highly correlated. There is evidence that body handles animal proteins differently from plant proteins. The source of the protein is equally important as a protein quantity. A high intake of animal protein is linked to heart disease, many cancers, high blood pressure, kidney disease, osteoporosis and kidney stone. A vegetarian diet is associated with a reduced risk of developing mentioned diseases.

Amino acids and disease prevention

Arginine: Plays an important role in wound healing, detoxification reaction, immune functions and promoting the secretion of insulin and growth hormone. Normally, the body makes enough arginine, but in some instances supplementation may prove useful. Foods high in arginine are chocolate, peanuts, seeds and nuts.
Leucine, isoleucine and valine: Essential amino acids, very important for the maintenance of muscle tissue and to preserve muscle store of glycogen, a storage form of carbohydrate that can be converted into energy. These amino acids are found in most high-protein foods, with diary products and red meat containing the greatest amount.
Glutamine: Involved in more metabolic processes than any other amino acid. Glutamine stimulates the synthesis and inhibits the degradation of proteins and is a energy source for muscle cell division. Whey protein and eggs are good sources of glutamine.
Lysine: Essential amino acid required for many body functions, growth and bone development in children, maintenance of lean body mass, production of antibodies, hormones and enzymes, collagen formation and repair of tissue. Higher intakes of lysine are useful for recovering from injuries or operations. Food high in lysine are most vegetables, legumes, fish, turkey and chicken.