carbohydrate
د هدبل فاضل
introduction
*CHO are the most significant source of energy in the diet, about 50-60% of the energy come from CHO
Classification1- simple (sugars ie mono & dissachararcide)
2- complex (starch ie polysaccharide & oligosaccharide)
Monosaccharides: are the simplest CHO in that they can not be hydrolised to smaller CHO. Its include glucose, fructose & galactose.
Glucose is the simplest CHO, is found in fruits & vegetables.
Fructose is found in honey, fruits & vegetables
Diasaccharides: two joined monosaccharides are called disaccharide. Include sucrose, maltose, trehalos & lactose.
They are composed of 2 monosaccharides bound together by covalent bond known as glycosidic linkage.
Sucrose is the commonest disaccharides & is extracted from sugar beat or sugar cane.
Oligosaccharides &
polysaccharides:
Are composed of longer chains of monosach. Units bound together by glycosidic bonds.
Oligosach (raffinose, stachyose, human milk oligosacch). Typically contain two & nine monosach. Units, & polysacchs. Contain greater than 10 monosach units.
Polysach represent an important class biological polymers.
Starch is used as a storage polysach in plants, it founds in the form of both amylose & the branched amylopectin.
Starch found in large quantities in cereals grains, potatoes, plantains.
Non-starch polysach : (NSP)-Fiber: can be classified as soluble (like apples, legumes, pears, strawberries) or insoluble (like beans, brown rice, maize, peas, breads, cereals, pasta).
Insoluble fibers consist mainly cellulose & hemicelluloses. It bind to water in the colon, & stimulate peristalsis in the colon & reduce risk of constipation & ca colon.
Soluble fiber blunts the response of blood glucose to ingestion. The re absorption of bile acid is slowed by soluble fiber so increase cholesterol loses in feces & reduce blood choles level.
sources
Grain products: rich sources of complex & simple CHO. Foods high in CHO include breads, pastas, beans, potatoes, vegetables, fruit, milk products, rice & cereals .
functions
1- provision of energy: dietary CHO have energy value of 4 kcal/g. number of CHO are only partly or not at all digested in the small intestine & are fermented in the large bowel to short chain fatty acids, these include the non-digestable oligosach, resistance starch & NSP.
The processes of fermentation is metabolically less efficient than absorption in the small intestine & these CHO provide the body with less energy.
2- effects on satiety /gastric emptying.
3- control of blood glucose & insulin metabolism: absorbed CHO cause an elevation of the blood glucose conc .
Insulin is secreted as a response to blood glucose elevation.
4- protein glycosylation: the non-enzymatic glycation of proteins is dependant on the conc of glucose & fructose in blood & the half life of the protein.
5- cholesterol & TG metabolism:
increase in CHO containing food at the expense of fat may result in decrease in HDL & increase in VLDL & TG in blood.
6- bile acid dehydroxylation:
7- fermentation:
8- bowel habit/laxation/motor activity:
Dietry CHO & disesaes
1- obesity
2- NIDDM
3- cardiovascular diseases
4- cancer
5- increase CHO is very effective means in preventing & treating constipation , hemorrhoids & anal fissure.
6- dental caries
7- malnutrition
recommendationTo increase complex CHO & healthy nutrients:
*eat more fruits & vegetables.
*eat more whole grain rice, breads, & cereals
* eat more legumes(beans, lentils & dried peas).