Download Access Power Point Presentation

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
New Structural Protein
are Found in Tissue

Growing Child
•bone
•brain
•all organs
•immune system
•digestion
•vicious circle of malnutrition
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
Functional Proteins
Muscle contraction
 Transport proteins
 Enzymes

•
•
•
Digestion
Absorption
Metabolism
Amino Acids in Dietary Protein
Protein must first be digested . ie broken
up into it’s constituent Amino Acids
 Protein -> Peptides -> amino acids
 All proteins are polymers of amino acids
and may be hundreds of amino acids
long
 These include all 18 types amino acids

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
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

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)

Protein Requirement Based on Age






Age
1-3 mo
6 mo
g/ kg Body Wt /Day
2.00
1.50
1 yr
1.20
6 yr
Adult
1.00
0.75
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
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


Oxalic acid is made from some AA


causes osteoporosis and kidney stones
also causes kidney stones
All of these put more stress on the
kidneys
Hierarchy of Nutrients Used for
Energy?

Some say Carbohydrates used first then
Fat then Protein
NOT TRUE if adequate energy when
protein consumed
•
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
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 > intake means
growth
If NB = +ve intake > excretion means wasting
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
•These are ESSENTIAL Amino Acids and
•
must be supplied by the diet
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
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
Use of Essential Amino Acids
Essential Amino Acids in Diet
Essential AA Need vs. Supply
Amount of Essential AA Used
Limiting Amino Acid
Only in proportion to Essential AA is
least supply
 That determines amount of all protein
made

Essential Amino Acids wasted
Wasted Amino acids burnt for energy
 --> Specific Dynamic effect

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
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
Biological Value of Proteins











Whole egg
Milk
Fish
Beef
Soybeans
Rice, polished
Wheat, whole
Corn
Good mixed diet
Peas & Beans,
Millet
93.7
84.5
76.0
74.3
72.8
64.0
64.0
60.0
70.0
40.0
43.0
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