Amino acid metabolism works in several steps. First, food proteins are broken down into amino acids. (Protein molecules are made up of long chains of amino acids bonded to each other.) Then, the amino acids are absorbed into the bloodstream. The amino acids are then used in body cells to form new proteins for energy.
Protein foods are digested to amino acids in the gastrointestinal tract--starting in the stomach and being completed in the duodenum of the small intestine. The amino acids are then absorbed, and the absorbed amino acids are carried in circulating blood to the liver, from which they are distributed to different tissues, where they form a series of amino acid pools. As the body's different organs require protein synthesis for energy, they are supplied by these pools of amino acids that are stored in tissues.
Amino acids that are in excess of the body's needs are converted by liver enzymes into keto acids and urea. Keto acids may be used as sources of energy, converted into glucose, or stored as fat. Urea is excreted from everyone's body in sweat and urine.
Amino Acids From Protein
Ingestion of protein is required to supply amino acids for the formation of body protein. The amino acids of proteins can be divided into two nutritional categories: essential and nonessential. All 20 amino acids are required by our bodies.
The essential amino acids are:
The non-essential amino acids are:
Protein Foods and Amino Acids
Protein foods contain different types of amino acids. Different combinations of amino acid bonds are almost unlimited. Protein foods that contain all of the essential amino acids are complete proteins. Protein foods that do not contain all of the essential amino acids are incomplete. When two or more incomplete proteins are combined, they can make a complete protein.
How Much is Enough?
The amount of amino acids your body requires depends on your activity level and your body weight. For most people, eating 1 to 1.5 grams of protein per pound of body weight is a good amount. Athletes require more protein, as well as carbohydrates, and fats, because they burn more energy before, during, and after their workouts.
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