a third to a half of daily protein intake should be of animal origin. animal protein is fairly expensive so a mixture of animal and vegetables protein should be taken. cheaper cuts of meat are nutritious as dearer if correctly cooked. herrings are a cheap and valuable form of fish. cheese and eggs are excellent substitutes for meat. skimmed milk is as rich in protein as whole milk.
sources of food
plants take in carbon dioxide from air through their leaves and absorb water with dissolved mineral salts from the soil through thre roots.the green colouring matter in leaves are called chlorophyll, enables them to adsord energy from the sun. this energy is used to convert carbon dioxide and water in carbohydtares. from these and mineral salts, all other sunstances in the plant are formed.animals : either feed on green plants (herbivorous) or prey on other animals (canovorous)human : is both herbivorous and canivorous (a mixed diet is best for most people).
nutrients
all food is made up of chemical substances called nutrients;proteins : provide material for body building and repair; and are also used as a source of energycarbohydrate : provides energy which is needed for all bodily activities; some energy is liberated as heatfat : also provides energy which is needed for all bodily activities; it also acts as an insulatorminerals : provide material for body building and repair, protection from disease and maintenance body processesvitamins : protection from disease and maintenance of body processeswater : from a large proportion of all body materials - need for be classed as a body builder and regulator, transport materials within the body.
amino-acids
these are the simpler substances which make up protien; there are 22 amino-acid and different proteins contain different numbers and combinationsthere are 10 essential amino-acids which the body needs for growth and repaircomplete protein : these contain all the essential amino-acids and are of high biological valueincomplete protiens : lack one or more of the essential amino-acids and are called vegetable protiensprotein can compensate for each other's dificiency if taken together (cheese and bread) there are sufficient amino-acids in cheese to make good the deficiency in bread.
protein
protein is essential to life as all living cell are buil up of protoplasm which consists of protien, among other substancesproteins are made up of elements carbon, hydrogen, oxygen, nitrogen and usually phosphorus and sulphur; other elements may be present.
source of protein
complete protein : found mainly in animal foodmeat - myosin, fibrin (elastin)fish - myosineggs - white - albumeneggs - yolk - vitalin, globulinmilk - caseinogen, globulincheese - caseinogennuts, although vegetable, contain excelsin - a complete proteingelatin, although animal, lack four essential amino-acids and is not a complete protien but is a protein sparer; it helps to compasate other protein. soya bean flour is vegetable but a complete proteinincomplete protien (vegetable protein) : found manily in vegetable foodscereals - wheat - glutein and gliadin cereals - barley - hordinpulses - (peas, beans, lentils) legium
functions of protein
1. for growth and tissue repair especially for children, expectant and nursing mother.
2. secondary source of energy; note the danger in slimming diets of cutting down too much on fats and carbohydrates and not providing sufficient protein for body building and energy.
3. essential for the manufacture of normal body secretions.
proportiotion of complete and incomplete protein needed
a third to a half of daily protein intake should be of animal origin. animal protein is fairly expensive so a mixture of animal and vegetables protein should be taken. cheaper cuts of meat are nutritious as dearer if correctly cooked. herrings are a cheap and valuable form of fish. cheese and eggs are excellent substitutes for meat. skimmed milk is as rich in protein as whole milk.
