Ch. 4 Carbohydrates

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Lecture 3

• Ch. 4 Carbohydrates

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OverviewCarbohydrates

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

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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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.

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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.

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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

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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

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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

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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

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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

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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