Community Medicine
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Nutrition Lecture.2 Proteins
*Proteins are essential constituents of cells.
*They are complex organic nitrogenous compounds. They are composed of carbon,
hydrogen, oxygen, nitrogen and sulfur in varying amounts. Some proteins also contain
phosphorous and iron and occasionally other elements.
*Its building unit is amino-acid. Some 24 amino-acids are stated to be needed by the
human body, of which 9 are called essential because the body cannot synthesize them.
Recommended allowances of proteins is around (15%) of energy needed by the body.
[ 1 gm 4 Calories].
- Adult 1gm/Kg
- Children 3.5gm/Kg
- Adolescent 1.5gm/Kg
- Pregnancy need additional 20gm daily
- Lactating women need additional 40gm daily
Human body can convert many unnecessary amino-acids to amino-acids that are
needed .
There are nine amino-acids necessary for any adult person. Thus diet must contain them.
Essential amino-acids for adults are:-
1.Lucine . 2.Isolucine .
3.Lysine . 4.Methionine .
5.Phenylalanine . 6.Threonine .
7.Tryptophan . 8.Valine .
9. Histidine
Additional essential amino-acids for a growing child is Arginine, and for premature
babies are Cystine and Tyrosine.
Some essential amino-acids have important biological functions e.g. formation of niacin
from tryptophan, the action of Methionine as a donor of methyl groups for the synthesis
of choline, folates and nucleic acids.
X Proteins in different foods can be graded on the basis of whether they contain the
essential amino-acids in a satisfactory proportion to meet the human body needs
or not .
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Community Medicine
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Sources
1.Animal source proteins: usually contain all the essential amino-acids in a suitable
proportion.
Thus it considered a first class proteins. [Meat, Fish, Milk & its derivatives, and Eggs]
2.Vegetable source proteins: the amount of proteins in plant cells is small in general .
However, its amount is variable according to type of plant .
[Potatoes , Beans, Peas, Nuts, Bran]
Beans and peas contain highest protein among seeds.
Potatoes contain good amount of proteins.
Functions of proteins
1.Body building.
2.Repair and maintenance of body tissues.
3.Maintenance of osmotic pressure.
4.Synthesis of certain substances e.g. antibodies, plasma proteins, hemoglobin,
enzymes, hormones and coagulation factors.
5.Supply of energy when the calorie intake is inadequate.
Malnutrition illnesses
Two main groups of such illness :-
A-)Caloric deficiency (Starvation) :-
J Starvation is a term applied when there is partial or total deprivation of food and
water . This lead to gradual wasting of body tissues.
J Chronic starvation occur in many parts of the world.It is due to caloric content of
diet below minimal requirement and inadequate specific nutrients specially
proteins .
In children , there will be :-
1.Retardation of growth (failure to gain weight and height) .
2.Physical and mental activities are less .
3.Reduced resistance to infection .
J In adults , there will be :-
1.Emaciation .
2.Lethargy .
3.Vitamin deficiency .
4.Odema .
Community Medicine
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B-)Protein deficiency diseases:-
1.) Marginal hypo-proteinaemia:-
J It may accompany other pathological conditions .It may occur without starvation .
J It is fairly common complication of debilitating diseases .
J It may follow sever burns , extensive surgery , big wounds , gastric ulcers , liver
and kidney diseases .
J It may accompanied by edema but very rare .
Its etiology :-
1.Deficiency intake of protein(in quality and quantity) .
2.Failure of digestion and absorption .
3.Abnormal destruction or loss of amino acids (as in sever burn or nephritis) .
2.)Sever protein starvation with edema
J It is seldom encountered except during wars or famines where there is a
prolonged food shortage .
J There will be loss of weight,loss of appetite , reduced resistance and diminished
strength .
J It may be accompanied with other diseases .
J Laboratory investigations are used to confirm the diagnosis .
J There will be a delayed wound healing and postural edema .
Kwashiorkor disease
It is sever form of protein deficiency .
It is characterized by :-
1.)Retarded growth in late breast feeding , weaning and post weaning period .
2.)Alteration in skin and hair pigmentation (flag hair) .
3.)Odema .
4.)fatty infiltration with cellular necrosis and fibrosis in the liver tissue .
5.)Heavy mortalities (high mortality rates) .
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Factors affecting protein requirement
1.)Tissue growth :-
Any period of growth need additional proteins supplement in food .e.g.during pregnancy
, special periods during reproductive life .
2.)Diet :-
U Taking sufficient amounts of non protein calories in diet can play a protein sparing
effect for energy production .
U Also allowing a proper time interval between ingestion of proteins which lower its
competition at the absorption sites and enzymes .
3.)Illness or disease
The presence of any illness will increase the protein requirement specially illness
accompanied by high fever (because of tissue destruction and raised basal metabolic
rate) . Also in cases of extensive trauma , burns , major surgery , …etc .
Measures of protein requirements
Two basic measures are considered :-
1.)Protein quantity
Daily requirement for adult is (0.8 - 1 gm/Kg/day) , should take in consideration stage of
growth and development , pregnancy , lactation , and age.
2.)Protein quality
Since the value of protein depends on its content of Essential Amino Acids .
Examples