Lecture 4 carbohydrate

NDD10102 PRINCIPLES OF HUMAN NUTRITION

Lecture 4: CARBOHYDRATES: Sugars, Starches, and Fiber

DR. SHARIFAH WAJIHAH [email protected]


Topic learning Outcome

At the end of this lecture, the students should be able to:-1. Differentiate simple carbohydrates and

complex carbohydrate2. Describe the function of carbohydrates in the

body3. Demonstrate knowledge of health with

carbohydrates


Outline

• What are Carbohydrates?• Carbohydrate in the Digestive Tract• Carbohydrates in the Body• Carbohydrates and Health• Carbohydrate: One part of the total diet• Carbohydrates and Food Technology


WHAT ARE CARBOHYDRATES?


I (CH2O)n or H - C - OH

I

• Carbo-hydrate means carbon and water (C + H2O).

• For every carbon there is 1 water molecule or 2 hydrogen atoms and 1 oxygen atom.


Where do carbohydrates come from?

• Plants and photosynthesis– Chlorophyll captures light energy which is

transformed into chemical energy - ATP– Chemical energy is used to combine CO2 and H2O

to form glucose. **The by-product is oxygen.– Extra glucose is stored in plants as starch.– **Plants are the base of the food chain for all

living things.

NDD10102 PRINCIPLES OF HUMAN NUTRITIONFig. 4-1, p. 100

sun

energy

carbondioxide

chlorophyll

glucose

oxygen

water

energy

energy

energy

FIGURE 4-1: CARBOHYDRATE—MAINLY GLUCOSE—IS MADE BY PHOTOSYNTHESIS


• 2 categories– Simple CHO– Complex CHO

• Found grains, breads, legumes, fruits, vegetables, and milk as well as in sweeteners

Primary source of ENERGY used to fuel the body


Simple carbohydrate

Known as sugar (saccharides)

monosaccharides disaccharides(Single sugars, 6 carbons)• Glucose• Fructose• Galactose

REMEMBER: In the body, fructose and galactose are converted to glucose.

(2 sugars joined together chemically, 12 carbons)• Maltose• Sucrose• Lactose



Complex carbohydrate

oligosaccharides polysaccharides(containing 3-10 sugar units)• raffinose• stachyose

REMEMBER: In the body, oligo can not be digested in the stomach and small intestine

(containing many sugar units)• Glycogen (animals)• Starch & fiber

(plants)



Glycogen

• Storage form of CHO in animals• Stored in muscles and liver• Muscles glycogen: source of energy during

activity• Liver glycogen: provides glucose to cells

throughout the body via bloodstream


Starches• Storage form of CHO in

plants• TWO forms:-

– Amylose: consists of long straight chain of glu molecules

– Amylopectin: consists of branched chains of glu molecules


Fiber• Can not be digested by human enzymes• Can not be absorbed in the body• Beneficial health effects:

– Lowering blood cholesterol– Reducing constipation

• Dietary fiber: non-digestible CHO and lignin that are found intact in plants

• Functional fiber: isolated non-digestible that have been shown to have beneficial physiological effects in humans.

• Total fiber= dietary fiber + functional fiber


• Fiber cont’d– Two types:

• Soluble fiber– Fiber that dissolves in water or absorbs water and ca be broken

down by the intestinal microflora– i.e pectins, gums– Oats, apples, beans and seaweed

• Insoluble fiber– Fiber that, for the most part, does not dissolve in water and

cannot be broken down by bacteria in the large intestine– i.e cellulose, hemicelluloses and lignin– Wheat bran, rye bran, brocolli


ONE WAY FIBER IN FOOD MAY LOWER CHOLESTEROL IN THE BLOOD


• The small intestine can only absorb monosaccharides.

• Starch digestion begins in the mouth with and enzyme, amylase, that breaks it down into disaccharides – continues in storage section of the stomach.

• Small intestine – amylase from the pancreas continues starch digestion.

CARBOHYDRATE IN THE DIGESTIVE TRACT


• Disaccharides – are broken down into monosaccharides small intestine by enzymes produced in the walls of the small intestine.– Sucrase– Maltase– Lactase

• Monosaccharides are absorbed in small intestine and enter the blood stream.


• Blood carries monosaccharides to the liver.– All are converted to glucose.– Glucose travels to other cells via the blood.– Extra glucose is stored as glycogen in the liver and

skeletal muscles.


Carbohydrate digestion in the GI

tract


• Lactose intolerance – lack of the enzyme lactase causes inability to digest lactose in milk products.– There are few with complete intolerance, most

can ingest small quantities of milk products.– Some people are really allergic to milk. This

allergy seems to be increasing in infants.– Big Problem – calcium deficiency!


CARBOHYDRATES IN THE BODY

• Carbohydrate Metabolism– Body cells receive a constant supply of glucose via

the blood stream– Supply is regulated by the liver and by hormones

secreted from the pancreas– Once glucose reaches the cells, it is metabolized

to produce energy


Absorbed and travel via the hepatic portal vein to the liver

Glucose transported in the blood , reaching cells

What is happened if blood glucose levels rise too high or drop to low??



• Glycemic response– How quickly blood glucose levels rise after a meal– Affected by composition of the meal

1. Fat and protein consumed high CHO foods: Stomach to empty more slowly, delay the rates glucose enters the small intestine

2. Consuming sugar alone: Blood glucose increase rapidly

INFO: A mixed meal such as chicken, rice and vege which contains starch, fat, protein and fiber, will take 30 to 60 min before blood glucose begins to rise


• Glucose metabolism- 4 interconnected stages1. Glycolysis

• Takes place in the cytoplasm of the cell • splits glucose into two 3-carbon pyruvate molecules• The energy released from 1 molecule of glucose is used to

make 2 ATP

2. Citric Acid Cycle/Kreb Cycle• Occurs in mitochondria• 1 carbon is removed from pyruvate , leaving 2 carbons that

form Acetyl-CoA• Acetyl-CoA is broken down, releasing 2 molecules of Co2


GLYCOLISIS

KREB CYCLE


• Glucose metabolism- cont’d3. Electron transport chain

• Electrons are passed down a chain of molecules to oxygen to form water

• Energy is released and used to produce ATP

4. Gluconeogenesis• Synthesis of glucose from simple non-CHO molecules• Occurs in liver and kidney cells• Using protein to make glucose• Amino acids from protein are the primary source of carbon for

glucose synthesis• Essential for meeting the body’s immediate need for glucose

NDD10102 PRINCIPLES OF HUMAN NUTRITIONGLUCONEOGENESIS

ELECTRON TRANSPORT CHAIN

ELECTRON TRANSPORT CHAIN


• Fatty acids cannot be used to make glucose. WHY?– Reactions that break them down produce 2-carbon

molecules (acetyl-CoA)• However, CHO is needed to breakdown Fat

– Fatty acids are broken into molecules of Acetyl-CoA– Acetyl-CoA can be used to produce energy via the Kreb

Cycle ONLY if it can be combine with a 4- carbon oxaloacetate molecule derived from CHO metabolism


Fatty acids

C C CoAAcetyl-CoA

Ketone bodies

Used for energy

Excreted in urine

Accumulate in blood

Carbohydrate unavailable

Carbohydrate available

C C C Coxaloacetate

C C C CC C

Kreb Cycle

C O2

ATPH2O


• Ketone bodies:– Formed in the liver– Occur when there is not sufficient CHO to completely

metabolize the acetyl-CoA produced from fat breakdown– Can be used for energy in the heart, muscle and kidney (brain

obtain a portion of its energy)– Normal response to starvation or a very low CHO diet– Excess ketones are excreted by the kidney in urine– Fluid intake too low to produce enough urine to excrete

ketones, can build up in the blood causing ketosis• Symptom: headache, dry mouth, foul-smelling breath, reduction in

appetite


• Abnormal Glucose Regulation– Above the normal range= diabetes– Drop below the normal range= hypoglycemia

1. Diabetes mellitus– High blood glucose level

• Lack of insulin• Unresponsiveness of body cells to insulin

– Causes damage to the large blood vessels• Increased risk of heart disease and stroke

– Changes in small blood vessels nerves• Leading to kidney failure, blindness, nerve dysfunction and amputations


Diabetes Mellitus

• Type I diabetes: – Destruction of the insulin producing cells in the

pancreas (autoimmune disease - genetics, viruses, and other toxins have been implicated).

– Symptoms: polyuria, glucosuria, polydipsia– Strikes children and young adults. All are insulin

dependent, i.e. must have insulin injections.


Diabetes Mellitus

• Type 2 diabetes: – Cells become insulin resistant. Causes: genetic

predisposition, obesity)– Symptoms – same as for Type I– Affects older adults, obese children and

adolescents. Often controlled by diet and weight loss, however many must take insulin stimulating drugs or insulin injections.


Diabetes Mellitus

• Complications – both Type 1 and Type 2– Compromised immune system – infections– Blindness– Loss of limbs– Kidney failure


Diabetes Mellitus

• Control– Limit carbohydrate intake & protein intake. The

exchange system was originally designed for diabetics.

– Exercise is an important ingredient in the control of diabetes.


• Gestational Diabetes• Occurs in women during pregnancy (hormonal

changes)• Increase the risk of complications for the unborn

child• Disappears once the pregnancy is complete

Diabetes Mellitus


Hypoglycemia

• Symptoms - dizziness, confusion, weakness, death– Fasting hypoglycemia:

– Postprandial hypoglycemia:

– Also occurs with serious diseases.


CARBOHYDRATE AND HEALTH

1. Dental Caries – Formed when bacteria

that live in the mouth metabolize sugar from the diet and produce acid that cause cavities

– Particularly sucrose- most rapidly utilized food source for microbes


2. Heart Disease– High sugar intake

adversely affect blood lipid levels--- > increase the risk of heart disease

– Diets high in whole grains and fiber reduce the risk of heart disease, especially soluble fiber

– Diet high in fiber-rich foods reduce blood cholesterol


3. Chronic bowel disorders– Diet high in fiber can relive /

prevent • Fiber add bulk and absorb

water, making the feces larger and softer and reducing amount of pressure needed for defecation

– Helps reduce the incidence of constipation and hemorrhoids (swelling of veins in the rectal or anal area)


CARBOHYDRATE: ONE PART OF THE TOTAL DIET

• Recommendations for CHO intake– RDA: 130g/day (based on the av. min amount of glucose

used by the brain)– The FAO/WHO (1998) suggested total carbohydrate intake

should be 55-70% of total energy for prevention of diet-related chronic diseases.

– TSC on Energy and Macronutrients recommend sugar intake to be no more than 15% of total energy

– For fiber, an AI is set at 38g and 25g per day for young adult men an women, respectively, based on the amount of fiber needed to reduce heart disease risk


• Determine your CHO intake1. Determine

• The total energy (kcal) intake for the day• The grams of CHO in the day’s diet

2. Calculate Energy from CHO• CHO provides 4 kcal per g• Multiply grams of CHO by 4 kcal per g

3. Calculate % energy from CHO• Divide energy from CHO by total energy and multiply

by 100 to express as a percent


• Example:– A diet contains 2500 kcal and 350g of CHO

350 g of CHO x 4 kcal/g = 1400 kcal of CHO

1400 kcal of CHO x 100 = 56% of energy (kcal) from CHO2500 kcal


• CHO exchange list– Used to give a quick estimate of the total amount

of CHO in a food or diet– One carbohydrate exchange equals 15 grams of

carbohydrate– Sample list : http://

dtc.ucsf.edu/pdfs/CarbohydrateExchangeLists.pdf

http://dtc.ucsf.edu/pdfs/CarbohydrateExchangeLists.pdf

http://dtc.ucsf.edu/pdfs/CarbohydrateExchangeLists.pdf


CARBOHYDRATE AND FOOD TECHNOLOGY

• Complex CHO as Additives– Added as thickeners:

• sauces, puddings and gravies• Soluble fiber pectin- preparation of jams and jellies

– Added as stabilizers• Simple CHO as Additives

– Added as sweeteners- mostly fructose• Corn syrup, molasses

– As preservatives• to prevent the growth of microorganism

– Used to color foods• Caramelized when heated


• Artificial sweeteners: sugar substitute– Used to replace energy-containing sweeteners– Provide little or no energy– Types of artificial sweeteners

• Saccharin: 200 to 700 times sweeter than sugar• Aspartame:200 times as sweet as sugar• Acesulfame K: 200 times as sweet as sugar• Sucralose: 600 times sweeter than sucrose• Sugar alcohols: sugar-free products


Summary

1. CHOs are chemical compounds that contain carbon, hydrogen and oxygen

2. In food they include sugar, starch and fiber3. Simple CHO include monosaccharides and

disaccharides4. Complex CHO are oligosaccharides and polysaccharides

(glycogen in animal and starch and fiber in plants)5. Fiber cannot be digested by enzymes in the human

stomach and small intestine and therefore is not absorbed in the body


6. In the body, CHO primarily as glucose, provides source of energy7. Glucose is metabolized through cellular respiratory involving glycolysis,

which breaks glucose into pyruvate; acetyl-CoA formation; the Kreb Cycle, which produces CO2 and electrons; and the electron transport chain which produces water and ATP

8. Blood glucose levels are maintained by the hormones insulin and glucagon. When blood glucose rises, insulin released, when blood glucose falls, glucagon is released

9. Diabetes is an abnormality in blood sugar regulation that occurs either because insufficient insulin is produced or because there is decrease in the sensitivity of body cells to insulin.

10. Hypoglycemia is a condition in which blood glucose falls to abnormally low levels, causing symptoms such as sweating, headaches and rapid heart beat.


11. Diet high in added sugar are low in nutrient density and increase the risk of dental caries

12. Guidelines for healthy diets recommend 55% to 75 of energy from CHO.

13. CHO are added to foods in processing as preservatives and to provide flavor, texture and color.

14. Complex CHO are added as thickeners and stabilizers while simple CHO are most frequently added as sweeteners

15. Artificial sweeteners or sugar substitutes are used to replace energy-containing sweeteners


Thank you for listening…

Health & Medicine

Lecture 4 carbohydrate