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Biochemistry
Lec: 3 Dr. Ahmed Dalalbashi
In agriculture societies the major portion of dietary carbohydrates is
starch, while in industrial societies, sugar provides a significant portion of
the diet.
The substitution of sugar for starch in the diet may increase the plasma
lipids in some people.
This change is also mainly responsible for the high prevalence of dental
caries and may have contributed to the increased prevalence of diabetes,
coronary and heart diseases.
Fiber in the diet:
Fibers in the diet promote more frequent bowel movements and soften
stool. Diets high in cereal fibers have been shown to reduce the
symptoms of diverticulosis, (a disease of the large intestines).
Persons who consume high fiber diets also excrete more fats, sterols and
bile acids in their stools and have been shown to have lower blood
cholesterol levels.
Thus it has been suggested that the amount of fiber in the diet may be a
factor in the prevention of atherosclerosis.
It has also been indicated that the reduction of fiber in the diet may be a
factor in the increased incidence of cancer of the colon.
New researches has indicated an important function of fiber and that it
delay hydrolysis of starchy food so give chance to insulin to released so
decreasing the incidence of diabetes.
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Protein in the diet:
The nutritive value of protein depends on the proportion of the essential
amino acids in its molecule, although all amino acids are required for
building new tissues.
Protein is divided into animal and vegetable proteins. Animal proteins are
more important than vegetables as they contain larger amount of essential
amino acids.
Protein requirements:
Protein requirements can be:
1. The requirement for the essential amino acids
2. Requirement for the total protein; which must be available to the
body for the synthesis of non-essential amino acids.
Protein allowance:
It has been recommended a daily intake of 0.8 g of protein/kg of body
weight for adults. Hence the recommendation for a 70-kg male is 56 g of
protein.
An additional amount of protein to allow for growth has been included in
the allowance for children in the age group from 1-18 years.
An additional 30 g / day has also been added for pregnancy from the
second month to the end of gestation, 20 additional grams is
recommended during lactation to cover the milk produced.
It is highly desirable that at least 1/3 of the daily protein intake be derived
from animal sources. It is also necessary that some good quality proteins
be included in every meal.
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Protein Deficiency:
If the dietary protein supply is insufficient, the cells lack amino acids for
their synthetic activities. The effect of this is clear in young child as
growth slows down or even stops.
The effect of protein deficiency is also on organs and tissues of adults.
The first tissue affected by protein deficiency is the mucosa of the
intestines and the glands, which secrete the digestive enzymes, in
consequence a failure to digest and absorb the food leading to diarrhea
and loss of water and electrolytes.
Also failure of the liver to maintained its normal structure and functions.
In addition fat accumulates in the liver cells, the liver also fails to
synthesis plasma albumin and this is liable to lead to edema.
Later, protein deficiency leads to a failure to maintain the structure of
skeletal muscles and the production of RBCs so muscle wasting and
anemia results.
Analysis of plasma proteins is frequently used as an index of protein
deficiency.
Total proteins 68 58-78 g/L
Albumin 43 35-56 g/L
Globulin 22 16-31 g/L
Fibrinogen 3 2-4 g/L
A plasma albumin concentration below 35 g/L means protein deficiency
and in severs deficiency states the level often falls to 15 g/L and
sometimes lowers.
The concentration of γ- globulin is often raised owing to the presence of
infections. A low plasma albumin and a high plasma globulin are
frequently found together where the people are poor with inadequate diet.
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Secondary protein deficiency or conditioned may arise as a
result of pathological process as follows:
1. Utilization of protein as a source of energy, owing to an inadequate
supply of carbohydrate and fat.
2. Loss of protein in the urine as a result of diseases of the kidneys.
3. Loss of protein from the body by other routes such as hemorrhage
or wounds.
4. Failure to absorb protein in various disorders of the intestine.
5. Failure of a damaged liver to synthesize protein particularly
albumin from amino acids absorbed from the intestines.
6. Damage to tissues (Trauma) e.g. injuries, burns, fractured bones or
surgical operations are followed by a period of negative nitrogen
balance. (More tissue protein is catabolic than the diets can
immediately replace).