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Ch. 4 Carbohydrates

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Lecture 3 Ch. 4 Carbohydrates – PowerPoint PPT presentation

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Title: Ch. 4 Carbohydrates


1
Lecture 3
  • Ch. 4 Carbohydrates

2
OverviewCarbohydrates
  • Sources of Carbohydrates
  • Simple Sugars
  • Complex Carbohydrates
  • Dietary Fiber
  • Digestion and Absorption
  • Functions
  • Blood glucose regulation
  • Dietary sweeteners

3
How do we get Carbohydrates ?
  • Figure p. 110
  • Process of Photosynthesis in Plants
  • Requires the elements Carbon, Hydrogen and Oxygen
  • Suns energy 6water 6CO2 -----gt 6O2
    glucose (C6H12O6)
  • simple sugar produced is metabolized to more
    complex forms for storage
  • Sugars, starches and dietary fiber

4
Mono and Di Saccharides(simple sugars)
  • Figure 4.1
  • Mono one
  • Glucose, galactose and fructose
  • Di two
  • Sucrose, lactose and maltose
  • glucose - major form, all others converted to
    glucose for use in our bodies
  • fructose - fruit sugar
  • galactose - combined with glucose is lactose
    found in milk products
  • (glucose-glucose) is maltose
  • (glucose-fructose) is sucrose

5
Complex Carbohydrates
  • Figure 4.3
  • Starches and dietary fiber (polysaccharides)
  • highly recommended forms of intake
  • Starches - digestible polysaccharides
  • storage form of carbs. in plants
  • vegetables, bread, pasta, rice, beans
  • amylose - straight chains of glucose
  • amylopectin - branched chain starch
  • Glycogen - branched glucose
  • more chains, increases rate of breakdown -
    utilize energy faster
  • animal storage in liver (blood glucose) and
    muscle (movement)
  • Not a dietary source of carbohydrate

6
Dietary Fiber
  • Indigestible polysaccharides.
  • Fig 4.4
  • Insoluble fibers - whole grains, flax, veg
  • cellulose, hemicellulose, lignin(non carb)
  • structural part of plants
  • do not dissolve in water
  • Increase bulk of feces, decreases intestinal
    transit time
  • Soluble Fibers - citrus fruits, oat, beans
  • pectin, gum, mucilage
  • inside and around plant cells
  • dissolve or swell in water
  • fiber rich foods are a mixture of both kinds of
    fiber

7
Dietary Fiber
  • Retains water, increasing bulk of stool,
    stimulates peristalsis and facilitates
    elimination
  • too little fiber, small hard stool, difficulties
    with elimination
  • hemorrhoids and diverticula
  • insoluble fibers increase stool size the most
  • require high fluid intake
  • may play role in preventing colon cancer

8
Dietary Fiber
  • Emphasize foods rather than fiber supplements
  • vitamin C, carotenoids, may be implicated in
    observed benefits
  • soluble fiber may reduce cholesterol as it
    attracts bile (produced from cholesterol) and
    leads to its elimination in stool
  • recommend 20-35 g per day
  • MODERATION
  • Table 4-6

9
Carbohydrates in Foods
  • The foods that yield the highest percentages of
    energy from carbohydrates
  • Table sugar, honey, jam, jelly, fruit, baked
    potatoes
  • Rice bread and noodles are all high 75
    carbohydrate
  • Peas, broccoli, oatmeal, beans, french fries and
    skim milk all contain moderate amounts
  • Fig 4.5
  • Emphasize grains, pastas, fruits and vegetables
  • Contain other beneficial nutrients

10
Sweeteners
  • Nutritive - provide energy
  • Sugars - all mono and disaccharides
  • Consumption of sucrose - 12-48 pounds per person
    in one year in US
  • high fructose corn syrup
  • sugar alcohols -
  • sorbitol, mannitol, xylitol, 1.5-3 kcal /g
  • Alternative- provide little energy
  • Saccharin - (1879)
  • 300 times sweeter than sucrose
  • Aspartame (nutrasweet/equal)- (1981)
  • amino acids and methanol, 200 times sweeter than
    sucrose
  • damaged by cooking
  • PKU (phenylketonuria)

11
Sweeteners
  • Alternatives
  • Acesulfame-K - (1988)
  • 200x sweeter than sucrose
  • no energy value
  • can be cooked
  • Sucralose -(1998)
  • 600 times sweeter than sucrose
  • can be cooked
  • excreted, not used for energy
  • WHY ALTERNATIVES?
  • Diabetics, calories, dental

12
Carbohydrate Digestion
  • Figure 4-6
  • Begins with cooking
  • salivary amylase (enzyme)
  • mixes with food, begins break down of starch
  • Digestion stops in stomach due to acidic
    environment
  • pancreatic amylase (enzyme)
  • released into small intestine to breakdown starch
    and small chains of glucose into maltose
    (disaccharide)
  • Sucrase, Maltase, Lactase (enzymes)
  • enzymes in wall of S I produce mono from
    disaccharides.

13
Carbohydrate Digestion
  • Undigested disaccharide's used by bacteria in LI,
    produces acid and gas (abdominal discomfort)
  • Lactose intolerance
  • people lack sufficient lactase, usually avoid
    dairy
  • can reintroduce lactose into diet slowly, small
    amounts are OK.

14
Carbohydrate Absorption
  • Single sugars, actively absorbed by cells in wall
    of SI (energy)
  • travel via portal vein to liver, to be converted
    into glucose
  • used mainly for energy 4 kcal/g or stored as
    glycogen
  • For red blood cells and nervous system, glucose
    is the only source of fuel
  • recommend minimum 55 of caloric intake

15
Functions of Carbohydrates
  • Energy source
  • Protein sparing effect
  • too little carbohydrate, leads to breakdown of
    body protein for energy
  • Ketosis
  • Low carbohydrate prevents proper metabolism of
    fats
  • production of ketones, altering acid/base balance
    and body functions
  • sweetener

16
Blood Glucose
  • Regulated very tightly
  • liver controls entry of glucose into body
  • Stores glucose from GI that comes via portal vein
  • Hyperglycemia -too high-125 mg/100ml
  • Glucose released in urine, diabetes
  • hypoglycemia - too low - 40 mg/100ml
  • irritable, headache, hungry
  • Mainly controlled by hormones from the pancreas
    and adrenal glands

17
Blood Glucose
  • Pancreatic hormones (fig. 4-7)
  • Insulin - released with onset of eating and
    increase in blood glucose
  • stimulates liver to synthesize glycogen and cells
    to take up glucose from the blood
  • Glucagon - released when blood glucose drops
  • stimulates breakdown of glycogen to glucose and
    its release from liver into the blood stream

18
Blood Glucose
  • Adrenal Gland
  • Epinephrine (aka adrenaline)
  • released in response to stress
  • increases blood glucose, promoting quick mental
    and physical action
  • Balance of all these hormones is necessary to
    maintain blood glucose
  • Exercise also stimulates uptake of glucose by
    working muscle
  • Multifaceted Control System

19
Recommended Carbohydrate Intake
  • No RDA, minimum 50 - 100 g
  • 55 of total calories
  • reduce fat, increase fiber intake
  • sugar intake below 10
  • average 16
  • only a problem if nutrient rich food is ignored
    in favour of sweet foods
  • Glycemic Index(GI) -blood glucose response in
    body - higher insulin release
  • Long term may have health impact - diabetes
  • Table 4.8 - High GI foods - baked and mashed
    potatoes, short grain white rice, honey, jelly
    beans, bagels
  • Avoid overeating high GI and sugar
  • Combine with lower GI foods
  • Exercise regularly
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