Milk protein consists of two major protein fractions, i.e. the whey protein and the casein. These two fractions have different structure and different characteristics.
Whey is one of two major sources of protein found in milk (the other is casein.) When cheese is manufactured from milk the curd (casein) is used and the whey is separated out. At this point, whey is about 92% water, 6.5% lactose, 0.9% protein and 0.2% vitamins, minerals and fat-soluble nutrients - not exactly your perfect bodybuilding food. Since whey protein is a byproduct of cheese manufacturing, it must be developed some processing methods in order to achieve the desirable protein concentrations and separate undesirable components.
There are three primary forms of whey protein - concentrate, isolate and hydrolyzed peptides (hydrolysates). To find the right type of whey protein, we must analyze the processing methods in two aspects. At what rate can we separate the undesirable components, and how human is the technology, at what rate can we conserve the natural benefits of the whey.
The whey protein is an extra high quality protein source, with the highest biological value, an exceptionally high BCAA content. The branched-chain amino acids (BCAAs) are leucine, isoleucine, and valine. They make up 35% of your muscle mass. Besides building cells and repairing tissue, they form antibodies, they are part of the enzyme and hormonal system, they build RNA and DNA and they carry oxygen throughout the body and regulate blood sugar level. BCAAs are considered essential amino acids because human beings cannot survive unless these amino acids are present in the diet. During intense weight training the BCAA's are involved in maintaining glucose homeostasis, and reserve glycogen stores. The BCAA's stimulate protein synthesis through insulin secretion/activation of the PI3K pathway, and through activation of mTOR.
One pathway through which protein synthesis can be increased is the phosphatodyl-inositol-3-kinase pathway (PI3K). PI3K regulates glucose uptake through GLUT4 translocation and also increases amino acid uptake. Insulin, the body's "storage" hormone, works by activating the PI3K pathway.
Intake of BCAA stimulates expression of the hormone leptin in adipocytes. Leptin is a hormone, which is involved in the regulation of metabolism, body weight, and appetite.
In addition the whey protein is is very easy to digest and efficiently absorbed into the body. Whey protein is absorbed faster form the intestines than any other protein source.
Whey protein contains some highly bioactive peptides. Those fractions help to strengthen the cardiovascular system, decrease the cholesterol level, enhance endogenous glutathione production and have an antithrombotic and pain-killer effect.
Whey protein concentrate are made by using a filtration technology. By varying the time of processing and filtration units it is possible to make concentrates 75-85% protein. Modern concentrates now contain as high as 80-85 % protein with reduced amounts of lactose, fat and cholesterol. In general the whey protein concentrates have higher levels of bioactive compounds. A good concentrates contain far higher levels of growth factors, such as IGF-1, TGF-ß1, and TGF-ß2 like any other sources. They contain much higher levels of various phospholipids, and various bioactive lipids, such as Conjugated Linoleic Acid and they often contain higher levels of immunoglobulins and lactoferrin.
The drawbacks of WPCs are they have slightly less protein gram for gram than an isolate, and contain higher levels of fat (though these fats may in fact have beneficial effects) and higher levels of lactose.
The term casein is derived from the words caseus (cheese). Casein protein makes up approximately 80% of the protein in milk. Casein is highly stable globular phopshoprotein. It can't be denaturized and our body digests it slowly.
The beneficial properties of casein are partly a result of the amino acid composition and partly a result of the active peptides (the unique amino acid chain configurations that make up casein).
Casein is a slow protein. When you consume casein, you will reach a peak in blood amino acids and protein synthesis between 5 to 6 hours. Casein dramatically slows the rate of protein breakdown, which makes it a great choice for a pre-bed supplement. Casein protein is also a good idea to use during the day to keep you full and to keep a constant supply of protein available between meals or snacks if you have a long period of time between them.
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Proteins 
