Diploma in Hospitality Management
Nutrition Lecture Five
Protein
W
hy does the body need protein?Dietary protein provides needed amino acids these are used to make new protein in the body
Protein is made in the body:
contractile, enzymes , Immunity etc.
P
rotein in New Tissue as a Child GrowthsLack of protein for the immune system and digestive enzymes creates a vicious circle of malnutrition in malnourished children.
The inability to make of these proteins makes it hard for the child to utilise what little dietary protein is available to it.
I
n Adult Tissue Structural Proteins:Turn over of existing tissue requires new protein in:
Intestine, blood, skin, bone, hair and other organs
Adult functional proteins are constantly synthesis:
eg Immune system, hair , muscle contraction;
transport proteins for digestion , absorption carriage in blood;
and enzymes are needed for metabolism of all other nutrients.
Use of amino acids in the body"
Dietary Protein must first be digested into constituent Amino Acids.
ie broken up into it’s constituent
All proteins are polymers of amino acids that may be hundreds of amino acids long
All proteins include 18 different type amino acids in their structure
And these 18 must all be present in the body for it to make any new protein
Note: If any one AA is missing no protein is made
Fortunately 9 of the 18 AA can be made from the other amino acids
How much protein do you need each day?
In the 1920s League of Nations recommended 1.0gm protein / Kg body weight
UN now recommend Adult needs 0.75 gm / Kg of body weight
Research indicated we may need as little as 0.50 gm / Kg
0.75 gm/Kg is considered safe minimum allowing for individual variation.
Children need more than adults / Kgm body wt.
All these values assuming normal mixed proteins (veg/meat)
Protein Requirement Based on 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
V
alue of High Protein DietsAll absorbed AA is transported to the liver and only the required amounts are realised into blood. All the rest burnt or converted into fat. This is because AA is toxic and only small amount can be tolerated in the blood stream. The toxicity is because some AA are used as neurotransmitters and others are analogues of hormones
Specific Dynamic Effect is the heat produced by liver when it burns up excess AA from a high protein diet
Danger of Dietary Protein Excess
Any protein consumed in excess of bodies needs is wasted as the excess AA are used for energy and the bi-products then have to be are excreted. Removing the bi-products can have adverse effects.
Bi–products of Amino Acid catabolism:
Urea;
Most AA nitrogen is converted into urea, which is non-toxic
Sulfate;
Sulfate is made from Sulfur containing AA and causes the body to loose more Ca+ in urine causes osteoporosis and
Oxalic acid;
Oxalic acid is made from some AA and increases the chance of also causes kidney stones
Uric Acid
Some people excrete excess N as uric acid that can cause gout if it precipitates in muscle and joints
All of these bi-products put more stress on the kidneys
Advantage of Low protein diets
Hierarchy of Nutrients Used for Energy
Some say Carbohydrates used first then Fat then Protein This is only true for Dietary protein if one is on a marginal diet In this case Carbohydrates give a SPARING EFFECT for protein
This hierarchy NOT TRUE if adequate energy and 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
N
itrogen BalanceNot 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 a measure of amino acids you can use:
NB = amount of Nitrogen consumed - amount excreted
If NB = 0 intake = excretion
This means no loss or gain of protein from the body
If NB= –ve excretion > intake
This means body is wasting away.
If +ve intake > excretion
This means Increased body mass
E
ssential Amino AcidsSynthesise protein needs all 18 amino acids
If one AA is missing NO protein is made
However 9 AA can be made from the others by Transamination
Transamination allows one amino acid to be converted into another.
These are
Essential Amino
Acids are the other 9 AA that can not be made form any other AAThese ESSENTIAL Amino Acids must be supplied by the diet
S
paring Effects for Essential Amino AcidsSome amino acids can be made from one other
Eg. Tyrosine can be made from Phenylalanine so one spares the other
Cysteine can be made from Methionine
Both counted as one essential AA
Histidine is essential for children not adults
In adults histidine is provided by bacteria growing in the gut.
We can survive with out arginine ie it is a non-essential amino acid
But growth is much faster if arginine is included in the diet.
N
utritional Value of ProteinThe value of a protein is the amount of the essential amino acid in least supply.
Once the essential amino acid in least supply is used up all remaining AA are used are for energy or stored as fat
All excess nitrogen is excreted as Urea
F
irst and Second Class ProteinA concept based of keeping rats in N balance
Bread dose not allow growth of rats
However Bread is OK for humans This is because rats grow faster than humans
The
Nutritional Value of Protein is a continuous measure from 0 to 100
M
easuring Nutritional Value of ProteinMeasure of % of absorbed N that is retained in the body retained
Protein Efficiency Ratio
Compares rate of growth of fed different protein diets
B
iological Value of ProteinsWhole 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
C
omplimentary ProteinsBV of many vegetable protein too low to sustain human growth.
However 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 (not 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
Amino Acids