Protein is broken down into
Proteins in food are long chains of amino acids that are broken down during digestion.
Polypeptides, which are the next stage in protein digestion, are shorter chains
Peptides are chains with even fewer links, which then break down into constituent amino acids
Individual amino acids are finally reassembled into the new proteins that are needed.
Breaking down and reassembling protein The proteins that are used by body cells differ from those found in foods, although both types consist of the same amino acids. After ingestion, the amino acids in foods are rearranged into the protein structures needed by the body.
CAUTION
If the carbohydrates and fats in a diet are not supplying sufficient calories – for instance, when an individual is on a strict diet or suffering from malnutrition – the body ivill burn protein instead. Using protein as a fuel may not leave enough for its primary function of cell production.
There are two distinct types of protein in the body-
insoluble structural proteins that are basically fibrous in form, and physiologically active soluble proteins, which have a globular structure.
The fibrous type includes such proteins as keratin in hair and nails, myosin in muscle tissue, collagen in connective tissues such as skin, tendons and cartilage, and fibrin found in scar tissue.
The physiologically active class of protein includes most of the enzymes involved in the metabolic activities of the body. This type of protein also includes a number of hormones, for example insulin and prolactin (milk secretion), haemoglobin, which transports oxygen in the blood, and the antibodies used in the body’s defence system.
Complementary protein food sources do not need to be eaten at the same meal, but they do need to be eaten at the next meal on the same day. This is because the body stores essential amino acids for only a few hours.
Matching your protein foods
The solid red line in this diagram shows the better combination of plant foods to obtain quality protein. The broken green line shows the combination that does not always provide complete protein.
