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Protein is a complex structure comprised of amino acids that the body uses to refuel and rebuild muscle tissue. While there are virtually limitless different kinds of protein, casein protein, the main source of protein found in milk, is a common source. Protein is also digested at different rates within the human body. Milk protein, for example, is digested by the human body very slowly, generally taking six to eight hours, as opposed to whey protein that takes only a couple of hours. Aside from being a source of protein, milk also provides the human body with additional vitamins and minerals that are needed for it to function at optimum capacity.
Milk protein serves many functions within the human body; however, two functions are considered essential. The first function that milk provides within the human body is as a source of energy for muscles when other energy stores are low. Under starvation conditions, the body will break down protein by way of gluconeogenesis, which converts the protein into glucose that can be readily used as energy. While this process only occurs when the body has broken down and used all of its available fat and energy stores, it is an important life-preserving role for protein.
The second and primary role of milk protein, as well as most other proteins in the human body, is to provide both essential and non-essential amino acids for muscle repair and growth. The human body makes use of 22 different amino acids, eight of which cannot be synthesized from other sources and are considered essential. It is important to note that the non-essential amino acids are still required to support life, despite their classification as "non-essential." Non-essential proteins are only referred to in this way when referencing the need to consume them on a daily basis.
Most all milk available for purchase provides 8 grams of milk protein per 8 ounce (240 milliliters) serving. The recommended daily allowance of protein for adult males is between 0.8 and 1.4 grams of protein per pound of body weight per day. For a 160-pound (73-kilograms) male of average height, this equates to a required intake of between 128 and 224 grams of protein per day. Milk protein, however, should never make up 100% of a person's protein intake. Protein should be consumed from as many different sources as possible, such as legumes, red and white meat, eggs, or possibly a protein supplement of some kind.