Nutrition Lecture Three

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Nutrition Lecture Five
Protein
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Why does the body need protein?

• Dietary protein provides needed amino acids
• Used to make new protein in the body
• Protein is made in the body for

• Structural proteins

• Functional proteins

• contractile
• enzymes
• transport

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New Structural Protein are Found in Tissue

• Growing Child

• bone
• brain
• all organs
• immune system
• digestion
• vicious circle of malnutrition

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New Structural Protein in Adult Tissue

• Adult body maintenance

• Turn over of existing tissue

• intestine
• blood
• bone
• other organs

• New tissue

• Immune system
• Hair
• Skin

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Functional Proteins

• Muscle contraction
• Transport proteins
• Enzymes

• Digestion
• Absorption
• Metabolism

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Protein Structure
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Amino Acids in Dietary Protein

• Protein must first be digested . ie broken up
  into its constituent Amino Acids
• Protein -gt Peptides -gt amino acids
• All proteins are polymers of amino acids and may
  be hundreds of amino acids long
• These include all 18 types amino acids

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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

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How Much do You Need?

• 1920s League of Nations recommended 1gm protein /
  Kg body weight
• UN now recommend Adult needs 0.75 grams /
  K.gram of body weight
• Research indicated we may need as little as 0.5
  gram / Kg

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Safe Minimum

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

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Protein Requirement Based on Age

• Age g/ kg Body Wt /Day
• 1-3 mo 2.00

• 6 mo 1.50

• 1 yr 1.20

• 6 yr 1.00

• Adult 0.75

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Value of Excess dietary Protein

• All absorbed AA are transported to the liver
• Only required amounts are realised into blood
• All the rest burnt or converted into fat
• Specific Dynamic Effect
• heat produced by high protein diet

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Danger of Excess Protein

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

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Hierarchy of Nutrients Used for Energy?

• Some say Carbohydrates used first then Fat then
  Protein

• NOT TRUE if adequate energy when protein consumed

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Sugar, Fat and Protein are all used all the time

• Muscles use fat for energy (when aerobic)
• Brain and RBC.s use only Glucose
• Liver uses excess amino acids first

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Nitrogen Balance

• Not all proteins are as good as each other
• Even if you eat the RDA you may still not be
  able to replace lost protein
• Nitrogen Balance is Measure of amino acids you
  can use
• Amount of Nitrogen consumed minus
  amount excreted

If NB 0 intake excretion
If NB -ve excretion gt intake means
growth
If NB ve intake gt excretion means wasting
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Essential Amino Acids

• Synthesise protein needs all 18 amino acids
• If one AA is missing NO protein is made
• 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

ESSENTIAL

• These are ESSENTIAL Amino Acids and
• must be supplied by the diet

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Sparing Effects for Amino Acids

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

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Nutritional Value Of Protein

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

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Use of Essential Amino Acids
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Essential Amino Acids in Diet
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Essential AA Need vs. Supply
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Amount of Essential AA Used
Limiting Amino Acid

• Only in proportion to Essential AA is least
  supply
• That determines amount of all protein made

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Essential Amino Acids wasted

• Wasted Amino acids burnt for energy
• --gt Specific Dynamic effect

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First and Second Class Protein

• Based of keeping rats in N balance
• Bread no good for rats OK for humans
• rats grow faster than humans .
• Nutritional Value Of Protein
• I really a continuous measure from 0 to 100

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Measure of Nutritional value

• Amino Acid Score
• of limiting AA compared to Ideal protein.
• Biological Value Of Protein
• Measure of absorbed N retained
• Protein Efficiency Ratio
• Rate of growth of Rats

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Biological Value of Proteins

• Whole egg 93.7
• Milk 84.5
• Fish 76.0
• Beef 74.3
• Soybeans 72.8
• Rice, polished 64.0
• Wheat, whole 64.0
• Corn 60.0
• Good mixed diet 70.0
• Peas Beans, 40.0
• Millet 43.0

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Complimentary Proteins

• BV of many vegetable protein too low
• The deficiencies of some can be made by the
  excess in others
• eg Wheat, Rice and Nut seeds are
• low in methionine but high in
  Lysine

• Legumes (nor peanuts) are
• low in Lysine but high in
  methionine

• These two groups are complimentary to each other

eg Peas and Rice or Wheat and beans
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The End