Transcript بسم الله الرحمن الرحيم

Community Medicine
Lecture -3-
Learning objectives
At the end of this lecture student would
be able to :
1-Determine carbohydrates constituents .
2-Classify carbohydrates .
3-Identify functions of carbohydrates .
4-Illustrate types of dietary fibers .
5-Discuss the role of dietary fibers in
managing certain health problems .
To a level accepted to the accreditation
standard of the College .
Carbohydrates
Carbohydrate is the main source of energy (4kcal).
 Carbohydrate is essential for the oxidation of fats and synthesis of
certain non essential amino acids .
Three main sources of carbohydrates (starch , sugar and cellulose)
.
 According to its constituents ,it is classified into:-
A-)Mono-saccharides or simple sugars including:1.)Glucose : This sugar occurs naturally in blood of living
animals and in fruits and plants juices.
2.)Fructose: It is part of cane sugar. It is the sweetest sugar
which present in plants juices, fruits and honey.
3.)Galactose:It is part of lactose molecule.
B-)Disaccharides
 It is composed of two monosaccharide molecules.
 It include :1.)Sucrose or the cane sugar which is composed of
glucose and fructose molecules. It occurs naturally
in sweet fruits roots such as carrot.
2.)Lactose
 It is similar to sucrose but less sweetie.
 It occurs in milk in all animals including man.
 It is composed of glucose and galactose molecules
 It is useful in keeping calcium in children.
 Usually it is secreted with urine during
late pregnancy and lactation .
3.)Maltose
 It is composed of two glucose molecules.
 It is naturally formed from starch.
C-)Polysaccharides
 Here ,several monosaccharides are linked together
forming:1.)Starch
 Multiple glucose molecules linked together to form
starch molecule
 It constitute a large proportion of human diet.
 Plants usually store a great part of its nutrients as a
starch.
 Unripe fruits contain starch mainly.
2.)Glycogen
 It is the only carbohydrate of animal origin.
 It is made inside the body from several glucose
molecules.
 It is stored in the liver and muscles to be considered as
a reserved fuel .
 This reserve is rapidly exhausted when a man is fasting
.
Note :- Saccharine, which is one of the sweetie taste
materials used in diabetes as a replacement material for
cane sugar ,is not a carbohydrate material .It has a no
energetic value towards human body .It is again a water
soluble material that can be used through weight
reduction food regimens of obese persons.
Functions of carbohydrates
I. Energy production
Carbohydrates are usually considered the main
source for human energy supplement in diet.
 Although fatty diet has a higher caloric value ,but
only a small amount of fatty materials are needed for
essential fatty acids supplement .
 Carbohydrates are important in maintaining the
energy reserve in human body.
 In adults :500 grams is stored in the liver and muscles in
form of glycogen.
10 grams are present in blood as a circulating
blood sugar .This amount of available glucose
provide energy for only 12 hours a day in moderate
activity.
Accordingly, each individual person should eat
carbohydrates at regular intervals.
II. Special functions of carbohydrates
1.Glycogen reserves provide energy and protect the
body cells from depressed metabolic function and
injury.
2.Protein -sparing action
Carbohydrates help in regulating protein metabolism as
the following mechanism :When sufficient carbohydrates are available in diet,
proteins are spared for tissue building rather than
energy production.
3.Antiketogenic effect
Carbohydrates has also a role in fat metabolism . Its
presence in diet determine how much fat will be broken
down for energy ,thus will affect ketone bodies
formation. So in cases of uncontrolled diabetes and in
starvation, too much oxidation of fatty materials will
results in ketone bodies accumulation leading to
ketoacidosis.
4.Fuel for heart muscle
Although fatty acids are preferred as fuel for heart
muscle ,glycogen is important fuel for emergency
contractile energy supplementation .In aged heart ,
poor glycogen stores and low carbohydrates intake
may cause cardiac insufficiency symptoms and
angina.
5.Central nervous system viability
There is no glucose reserve in brain . Thus , a
continuous glucose supply is essential to promote
brain tissues viability .
6.Dietary fibers functions :
a. Water absorption
bulk of stool and
tendency to constipation by encouraging bowel
movement .
b. Making stool soft and pass easier through
emulsification of fibers by bacterial action in large
bowel .
c. Reducing intestinal transit time of food
reducing possibility of putrefaction and formation of
gasses and toxic substances .
d. Inhibits fecal mutagen synthesis by changing colonic
PH and bacterial metabolism .
e. Reducing incidence of cancer of stomach and colon
(cancer has direct association with low fiber diet) .
f. Reducing incidence of IHD (bind to bile salts and
prevent its re-absorption and thus reducing cholesterol
level in circulation) .
g. Fibers , particularly gum and pectin , when ingested
with diet reduce postprandial glucose level in blood .
h. Too much fibers ingestion
absorption
of
valuable micronutrients (some vitamins and minerals
like iron & zinc and reduce their bioavailability) .
Note :
A daily intake of about 40 gm of dietary fibers is
desirable .
Dietary fiber
It is mainly non starch polysaccharide which is physiologically important
component of diet .
Types of dietary fibers
A-Cellulose form : which constitute the main framework
of plants .
Human being cannot digest cellulose because of lack
of enzymes which digest cellulose.
It form a bulk of food that regulate intestinal
movement (i.e. stimulate peristalsis ).
Its sources include vegetables ,seeds and bran.
B-Non -cellulose polysaccharides:- It includes :
1- Hemicellulose pectin .
2- Storage polysaccharides e.g. inulin.
3- Plant gums and mucilages .
All are degraded to a greater or lesser extent by micro
flora in human colon .
According to its solubility , dietary fibers classified
into :
1- Insoluble fibers (cellulose, hemicellulose and lignin)
2- Soluble fibers (pectins, gums and mucillages).
Total fiber content of certain foods (gm/10gm)
High (>10)
Medium(1-10)
Low(<1)
Nil
Wheat
Rice
Refined &
processed foods
Sugar
Jowar
Most vegetables
Fats/oil
Bajra
Most fruits
Milk
Ragi
Coconut
All types of meat
Maize
Seasam
Legumes
Almonds
Dhals
Dates
Fenugreek
Dietary fibers relation to certain health problems:
Several studies revealed a constant relation between
dietary fibers intake and the occurrence or prevention
of certain health problems such as gastro-intestinal
problems , cardiovascular problems , diabetes mellitus
and cancer.
A-In diabetes mellitus :1.It reduces fasting blood sugar.
2.It reduces glucose urea.
3.It reduces insulin requirement.
4.It increases insulin sensitivity.
5.It inhibit the post prandial hyperglycemia through
slowing carbohydrates absorption.
B-In obesity:1.It reduces energy density of diet.
2.It alter the normal responses.
3.It alter thermo genesis.
4.It reduces nutrients bioavailability.
C-In coronary heart disease:1.It inhibit the recirculation of bile acids.
2.It reduces the triglycerides and cholesterol levels.
D-In colonic cancer:It reduces the incidence of disease .
E-In gastrointestinal problems:(such as diverticulosis , hemorrhoids , constipation
and irritable bowel syndrome)
It increases the diameter of intestinal lumen.
Gastrointestinal function
*-Reduce the tendency to constipation by encouraging
bowel movement and absorb water with increasing
the bulk of the stool .
*-Making the stool soft and passage easier , so they are
resistant to digestion in the digestive tract . In large
intestine the bacterial action causes emulsification of
the fiber .
*- Reducing the intestinal transit time of food .It
drastically reduces the possibility of putrefaction and
formation of gases and toxic substances .
*- Inhibits faecal mutagen synthesis by changing colonic
pH and bacterial metabolism . Cancer of stomach and
colon have been linked directly to a low fiber diet .
Thank You