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Why does the body need protein? n Dietary protein provides needed amino acids n Used to make new protein in the body n Protein is made in the body for:

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Presentation on theme: "Why does the body need protein? n Dietary protein provides needed amino acids n Used to make new protein in the body n Protein is made in the body for:"— Presentation transcript:


2 Why does the body need protein? n Dietary protein provides needed amino acids n Used to make new protein in the body n Protein is made in the body for: Structural proteins Functional proteins contractile enzymes transport

3 New Structural Protein are Found in Tissue n Growing Child bone brain all organs immune system digestion vicious circle of malnutrition

4 New Structural Protein in Adult Tissue n Adult body maintenance Turn over of existing tissue l intestine l blood l bone l other organs New tissue Immune system Hair Skin

5 Functional Proteins n Muscle contraction n Transport proteins n Enzymes Digestion Digestion Absorption Absorption Metabolism Metabolism


7 Amino Acids in Dietary Protein n Protein must first be digested. ie broken up into it’s constituent Amino Acids n Protein -> Peptides -> amino acids n All proteins are polymers of amino acids and may be hundreds of amino acids long n These include all 18 types amino acids

8 To make new protein you must have all 18 amino acids –You must have all 18 Amino acids to make any protein –If any one AA. Is missing no protein is made –9 of the 18 AA can be made from other amino acids

9 How Much do You Need? n 1920s League of Nations recommended 1gm protein / Kg body weight n UN now recommend Adult needs 0.75 grams / K.gram of body weight n Research indicated we may need as little as 0.5 gram / Kg

10 Safe Minimum n 0.75 is considered safe n allowing for individual variation. n Children need more / Kg body wt n Assumes a normal diet of mixed proteins (veg/meat)

11 Protein Requirement Based on Age n Age g/ kg Body Wt /Day l 1-3 mo 2.00 6 mo 1.50 1 yr 1.20 6 yr 1.00 Adult 0.75

12 Value of Excess dietary Protein n All absorbed AA are transported to the liver n Only required amounts are realised into blood –All the rest burnt or converted into fat n Specific Dynamic Effect –heat produced by high protein diet

13 Danger of Excess Protein n Excess AA are used for energy and the bi-products excreted n Urea is made from the nitrogen in AA n Sulfate is made from S in AA –This causes the body to loose more Ca+ in urine n causes osteoporosis and kidney stones n Oxalic acid is made from some AA n also causes kidney stones n All of these put more stress on the kidneys

14 Hierarchy of Nutrients Used for Energy? n Some say Carbohydrates used first then Fat then Protein NOT TRUE if adequate energy when protein consumed

15 Sugar, Fat and Protein are all used all the time: n Muscles use fat for energy (when aerobic) n Brain and RBC.s use only Glucose n Liver uses excess amino acids first

16 Nitrogen Balance n Not all proteins are as good as each other n Even if you eat the RDA you may still not be able to replace lost protein n Nitrogen Balance is Measure of amino acids you can use: n Amount of Nitrogen consumed minus amount excreted If NB= 0 intake = excretion If NB = -ve excretion > intake means growth If NB = +ve intake > excretion means wasting

17 Essential Amino Acids n Synthesise protein needs all 18 amino acids n If one AA is missing NO protein is made n 9 AA can be made from any of the others Transamination allows one amino acid to be converted into another. These are NON-ESSENTIAL amino acids The other 9 AA that can not be made form any other AA These are ESSENTIAL Amino Acids and must be supplied by the diet ESSENTIAL

18 Sparing Effects for Amino Acids n Some amino acids can be made from one other n Tyrosine can be made from Phenylalanine –so one spares the other –both counted as one essential AA n Tryptophane is essential for children not adults – In adults it is provided by bacteria in the gut. n We can survive with out arginine growth is much faster if it is included in the diet. n Need for optimal nutrition –Other “non - essential” amino acids may be similar

19 Nutritional Value Of Protein n The VALUE of a protein is the amount of the essential amino acid in least supply. n All additional AA consumed are used for energy or stored as fat n All excess nitrogen excreted as Urea

20 Use of Essential Amino Acids

21 Essential Amino Acids in Diet

22 Essential AA Need vs. Supply

23 Amount of Essential AA Used n Only in proportion to Essential AA is least supply n That determines amount of all protein made Limiting Amino Acid

24 Essential Amino Acids wasted n Wasted Amino acids burnt for energy n --> Specific Dynamic effect

25 First and Second Class Protein n Based of keeping rats in N balance n Bread no good for rats OK for humans n rats grow faster than humans. n Nutritional Value Of Protein –I really a continuous measure from 0 to 100

26 Measure of Nutritional value n Amino Acid Score –% of limiting AA compared to Ideal protein. n Biological Value Of Protein –Measure of % absorbed N retained n Protein Efficiency Ratio –Rate of growth of Rats

27 Biological Value of Proteins n Whole egg 93.7 n Milk 84.5 n Fish 76.0 n Beef 74.3 n Soybeans 72.8 n Rice, polished 64.0 n Wheat, whole 64.0 n Corn 60.0 n Good mixed diet 70.0 n Peas & Beans, 40.0 n Millet 43.0

28 Complimentary Proteins n BV of many vegetable protein too low n The deficiencies of some can be made by the excess in others n eg Wheat, Rice and Nut seeds are : n low in methionine but high in Lysine Legumes (nor peanuts) are: low in Lysine but high in methionine eg Peas and Rice or Wheat and beans These two groups are complimentary to each other


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