Chapter 5: Carbohydrates

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Chapter 5 Carbohydrates
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Monosaccharides

• Structure
• Glucose
• Fructose
• Galactose

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Fructose

• Metabolized to glucose in the liver
• Metabolized to glycogen
• Metabolized to lactic acid
• Found in fruit, honey, and high fructose corn
  syrup

4
Galactose

• Usually bound with glucose (lactose)
• Converted to glucose in the liver
• Available fuel source

5
Disaccharides

• Glycosidic bond
• Condensation reaction
• Alpha glycosidic bond
• Beta glycosidic bond
• Maltose (Gluc Gluc) --alpha bond
• Sucrose (Gluc Fruc) --alpha bond
• Lactose (Galactose Gluc) --beta bond

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Complex carbohydrates

• Oligosaccharides raffinose stachyose
• Polysaccharides Starch Glycogen
• Dietary fiber

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Oligosaccharides

• 3-10 monosaccharides
• Found in beans and legumes
• Not digested
• Metabolized by bacteria in the large intestine
• Beno

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Polysaccharides Starch

• 3,000 or more monosaccharides bound together
• Starch--alpha glycosidic bond
• Amylose--straight chain polymer
• Amylopectin--highly branched polymer
• Modified food starch and gel formation

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Polysaccharide Glycogen

• Storage form of CHO for animals and humans
• Structure similar to amylopectin
• More sites for enzyme action
• Found in the liver and muscles

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Dietary Fiber

• Undigested plant food
• Beta glycosidic bond
• Insoluble fiber
• Cellulose, hemicellulose, lignin
• Not fermented by the bacteria in the colon
• Soluble fiber
• Gum, Pectin, Mucilage
• Fruit, vegetable, rice bran, psyllium seed

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Soluble and Insoluble Fiber
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Bacterial Metabolism of Soluble Fiber

• Short-chain fatty acids
• Enhance the health of the large intestine cells
• Fuel source
• Absorbed into the blood stream
• Yields kcal

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Content Review

• What is a monosaccharide?
• What is a polysaccharide?
• What is glycogen?
• What are soluble and insoluble fiber?
• Which carbohydrate is resistant to human
  digestion?

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Digestion of Carbohydrate in the Mouth

• Saliva contains amylase
• Starch is broken down to dextrins and maltose
• Taste the sweetness with prolonged chewing

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Digestion of Carbohydrate in the Stomach

• The acidic environment stops the action of
  salivary amylase
• No further starch digestion occurs

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Digestion of carbohydrate in the Small Intestine

• Pancreatic amylase is released
• Intestinal cells release maltase, sucrase, and
  lactase
• Maltose maltase glucose
  glucose
• Sucrose sucrase glucose
  fructose
• Lactose lactase glucose
  galactose
• Monosaccharides are absorbed

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CHO Digestion
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CHO Absorption

• Glucose and Galactose
• Active absorption using a sodium pump
• Energy is expended to pump the sodium back out of
  the cell
• Going from low concentration gradient to high
• Fructose
• Facilitated diffusion using a carrier
• No energy expended

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Active Absorption
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Portal Vein

• Transports absorbed monosaccarhides
• Delivers them to the liver
• Liver can
• transform them to glucose
• release them back to the blood stream
• store as gylcogen (or fat)
• Resistant starch

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Functions of Carbohydrate

• Supplies energy
• Protein sparing
• Prevents ketosis
• Sweetener

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Health Benefits of Dietary Fiber

• Promotes softer, larger stool and regularity
• Slows glucose absorption
• Reduces blood cholesterol
• Reduces heart disease
• Reduces hemorrhoids and diverticula

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Diverticula
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Recommended CHO Intake

• RDA is 130 g/day for adults
• 50-100 gm of CHO/day to prevent ketosis
• Recommendation 45-65 of total energy
• Current intake
• 180-330 gm of CHO/day (primarily from white
  bread, sodas, baked goods)
• 50 of total kcals
• Worldwide the CHO intake is 70

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Recommended Dietary Fiber Intake

• Adequate intake is 25 g/day for women,
• 38 g/day for men (14g/1000 kcal)
• Daily Value 25 g/day
• (Children age 5 gm/day)
• Ave. U.S. intake 13-17 gm/day
• Too much fiber (gt60 gm/d) will
• require extra intake of fluid
• bind to some minerals
• develop phytobezoars
• fill the stomach of a young child quickly

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Recommendation for Simple Sugar Intake

• Low nutrient density
• Recommends no more than 10 of total kcal/day
  (upper limit at 25)
• Ave. U.S. intake 16 of total kcal/day
• Added to food and beverages during processing
• Not included in this intake are natural sugars
  (fructose, lactose)

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High Sugar Diets

• Empty calories
• Soda replacing milk
• Calories adding to excess
• Dental caries
• exposure to teeth
• High glycemic index
• Blood glucose response of a given food
• Influence by various factors

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Glycemic Index

• The blood glucose response to a given food
  compared to a standard
• Influenced by the amount of starch, fiber,
  processing, structure, and presence of other
  macronutrients

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Glycemic Load

• (The amount of CHO in a food) x (GI of that CHO)
• Better reflection of foods effect on blood
  glucose

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Effect of High Glycemic Load

• Stimulates the release of insulin
• Insulin increases blood triglycerides level
• Insulin increases LDL
• Insulin increases fat synthesis
• Increases risk for CVD
• Returns to hunger quicker
• Muscle may become resistant to the insulin

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How to decrease glycemic load

• Not overeat high glycemic load foods
• Combine a low glycemic load food with a high one
• Maintain healthy weight
• Regular physical activity

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Lactose Maldigestion

• Reduction in lactose
• Lactose is undigested and not absorbed
• Lactose is metabolized by large intestinal
  bacteria
• causes gas, bloating, cramping, discomfort
• Primary lactose intolerance disease
• Secondary lactose intolerance disease

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What To Do If You Have Lactose Maldigestion?

• Determine tolerated amount you can tolerate
• Eat dairy with fat
• Cheese is usually tolerated well
• Yogurt is usually tolerated well
• Use of Lact-Aide

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Content Review

• What is the main function of CHO?
• What can happen if you eat too few CHO?
• What is gluconeogenesis and what is its source?
• What are the health benefits of eating fiber?
• What are the harms in eating too much sugar?
• What is lactose maldigestion?
• Why should you try to eat low glycemic load
  foods?

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Sweeteners

• Sucrose--benchmark of all sweeteners
• Same caloric content (4 kcals/gm)
• No health benefit over another

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Types of Sweeteners

• High-fructose corn syrup
• 40-90 fructose
• cornstarch treated with acid and enzymes
• conversion of glucose into fructose
• same degree of sweetness as sucrose
• cheaper and used in many food products
• Brown sugar
• Maple syrup
• Honey
• Sugar alcohols
• 1.5-3 kcal/g
• Absorbed and metabolized slower
• Large amounts cause diarrhea

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Sugar Substitutes

• Saccharin
• 180-200x sweeter than sucrose
• Used in over 90 countries
• Initial studies showed excessive intake is linked
  to bladder cancer in lab animals
• No longer considered having cancer causing
  potential
• Not a potential risk in humans

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Aspartame (NutraSweet)

• Composed of phenylalanine, aspartic acid, and
  methanol
• 180-200x sweeter than sucrose
• 4 kcal/gm, but only a trace amount is needed to
  sweeten foods
• Not heat stable
• Complaints of sensitivity to aspartame
• headaches, dizziness, seizures, nausea, etc.
• Not recommended for people with phenylketonuria
  (PKU)

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Neotame

• 7000 13000 times sweeter than sucrose
• Structure is similar to aspartame (but not a risk
  for PKU)
• Heat stable
• Safe for use by the general population (including
  children, diabetics, pregnant and lactating women)

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Acesulfame-K (Sunette)

• K for potassium
• 200x sweeter than sucrose
• Not digested by the body
• Heat stable

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Sucralose

• 600 x sweeter than sucrose
• Substitute 3 chlorines for 3 hydroxyl groups on a
  sucrose
• Heat stable
• Excreted in feces (small amount in urine)

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Content Review

• What are the advantages of using one type of
  sugar over another?
• What are sugar alcohols?
• Why are there such little calories in sugar
  substitutes?

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Regulation of Blood Glucose

• Hyperglycemia
• Hypoglycemia

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Blood Glucose Control

• Role of the liver
• Regulates glucose that enters bloodstream
• Role of the pancreas
• Release of insulin
• Release of glucagon
• Maintain Homeostasis

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Functions of Insulin

• Promotes glycogen synthesis
• Increases glucose uptake by the cells
• Reduces gluconeogenesis
• Net effect lowers the blood glucose

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Functions of Glucagon

• Breakdown glycogen
• Enhances gluconeogenesis
• Net effect raises blood glucose

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Other Hormonal Influence

• Epinephrine/norepinephrine
• fight or flight response
• breakdown glycogen
• raises blood glucose
• Cortisol and growth hormone
• increase gluconeogenesis
• raise blood glucose

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Factors in Glucose Control
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Diabetes Mellitus--Type 1

• Genetic link
• Decreased release of insulin
• Insulin dependent
• Resulting in hyperglycemia
• Autoimmune disorder

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Treatment for Type 1

• CHO counting
• Insulin therapy
• Risk for heart disease

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Diabetes Mellitus--Type 2

• Genetic link
• 80 is associated with obesity
• Non-insulin dependent to start
• Accounts for majority of cases of DM
• Defective insulin receptors on the cells
• Over secretion of insulin to compensate
• Leads to beta cells failure
• Treatment medication and diet therapy (weight
  loss)

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Consequences of Uncontrolled Blood Glucose

• Ketosis leading to ion imbalances, dehydration,
  coma, death
• Degenerative diseases
• Nerve damage, Heart disease, Kidney disease,
  Blindness
• Atherosclerosis
• Increase risk for wound infections

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Hypoglycemia

• Reactive hypoglycemia
• Occurs 2-4 hours after eating a meal
• Possibly due to over secretion of insulin
• Fasting hypoglycemia
• Usually caused by pancreatic cancer
• Leads to overproduction of insulin