2. Polysaccharides
The term polysaccharide is used when from three
to thousands of sugar molecules are linked together.
There are two classifications of polysaccharides;
plant and animal.
1- Plant Polysaccharides
a- Starch:
The storage form of carbohydrate in plants, is the
most familiar form of plant polysaccharide.
3. It is found in seeds, corn, and the various grains
from which bread, cereal, spaghetti, and pastries are
made
Large amounts are also present in peas,
beans, potatoes, and roots, where it serves as an
energy store for future use by plants.
4. b- Fibers :
is classified as a non-starch polysaccharide,
of which cellulose is the most abundant organic
molecule on earth.
Non-starch fibrous materials are resistant to
human digestive enzymes., although a portion
are fermented by intestinal bacteria and
ultimately used in metabolic reactions following
their intestinal absorption.
5.
6. • - Fibers are found exclusively in plants and
make up the structure of leaves, stems, roots,
seeds, and fruit coverings.
-The various fibers differ widely in physical and
chemical characteristics and in physiologic
action.
• -They are found mostly within the cell wall as
cellulose, pectin, and the non-carbohydrate
lignin.
7. Health Implications
- Fibers hold considerable water and thus give
"bulk" to the food residues in the small
intestine, often increasing stool weight and
volume by 40 to 100%.
- This bulking action may aid gastrointestinal
functioning by exerting a scraping action on the
cells of the gut wall, صنفرة
8. 1-by binding or diluting harmful chemicals or
inhibiting their activity and
2- by shortening the transit time for the passage
of food residues (and possibly carcinogenic
materials) through the digestive tract.
This may reduce the chances of contracting
colon cancer and various other gastrointestinal
diseases later in life.
9. - Fiber intake also may cause modest reductions
in serum cholesterol in humans ,especially the
water –soluble mucilaginous fibers such as
pectin and guar gum present in :
Oats , Beans , Brown Rice , Peas , Carrots,
and a variety of Fruits.
For men with elevated blood lipids, for example
adding 100 gm of Oat bran to the daily diet
…..13% reduction in serum cholesterol-
10. • Some types of fiber may actually hinder
cholesterol absorption, while others may
reduce cholesterol metabolism in the
gut.
• These actions would depress the
synthesis of cholesterol while at the
same time facilitating the excretion of
existing cholesterol bound to the fiber in
stools.
11. • Dietary fiber also slows the rate of
carbohydrate digestion …absorption of
carbohydrates more slowly…..control of
glucose metabolism and DM.
• Fiber decreases the total number of calories
that will be consumed in subsequent meals.
12. Importance of Fibers
•
High intake of fibers… Reduction of:
1- Obesity.
2- Diabetes Mellitus.
3- Constipation.
4- Hypercholesterolemia.
5- Colon Cancer.
6- Cardiovascular Disease.
7- Metabolic syndrome
Fibers…Antioxidants and Phytochemical properties.
14. II. Animal polysaccharide
Glycogen:
is the storage carbohydrate peculiar to
mammalian muscle and liver.
It is a large polysaccharide polymer
synthesized from glucose in the process of
glycogenesis and stored in the tissues of
animals.
15. - In well-nourished humans, approximately 375
to 475 gm of carbohydrate is stored in the body.
- Of this, approximately 325 g is muscle
glycogen (largest reserve),
- 90 to 110 g is liver glycogen (highest
concentration that represents between 3 to 7%
of the liver’s weight), and only about 5 g is
present as blood glucose. `
16. As each gram of glycogen contains 4 calories
of energy, the average person stores between
1500 and 2000 calories as carbohydrate.
This is approximately enough energy to power
a 20-mile run.
17. Several factors determine the rate and quantity
of breakdown and synthesis of glycogen
•
1- During Exercise:
-
Muscle glycogen is the major source of
carbohydrate energy for the active muscles in
which it is stored.
-
In the liver , in contrast, glycogen is
reconverted to glucose and transported in
blood for use by working muscles by the
process of glycogenolysis
18. Glycogenolysis provides a rapid extra
muscular supply of glucose for muscular
action.
When liver and muscle glycogen is depleted
through :
- dietary restriction or heavy exercise….
Glucose synthesis from structural
components of other nutrients , principally
proteins through the gluconeogenetic
pathways.
19. Hormones :
play an important role in regulating liver and
muscle glycogen stores by controlling the level
of circulating blood sugar.
When blood sugar level is elevated , the beta cells
of the pancreas secrete additional insulin and
the excess circulating glucose is taken up by the
cells ,which inhibits further insulin secretion.
20. In contrast , if blood falls below normal, the
opposing hormone of insulin…. Glucagon is
immediately secreted by alpha cells of the
pancreas to normalize the blood sugar level.
Glucagon hormone raises the blood glucose
level by stimulating both :
- Glycogenolysis and gluconeogenesis in the
liver.
21. Recommended Dietary Carbohydrate Intake
• The typical American diet includes between 40 and
50 % of its total calories as carbohydrates.
• For a sedentary 70-kg person , this amounts to
daily intake of about 300 gm of carbohydrates.
• For more physically active people and those
involved in exercise training, about 60% of daily
calories (400-600 gm) should be carbohydrates,
predominantly of the unrefined , fiber rich complex
variety in fruits
22. Role of carbohydrates in the body
• 1- Energy source… the main function of
carbohydrate is to serve as energy fuel
particularly during exercise.
• 2- Protein Sparing…
• 3- Metabolic primer..
• 4-Fuel for the CNS.
