Chapter 4: The Carbohydrates: Sugars, Starches, and Fibers

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The
Carbohydrates:
Sugars, Starches,
and Fibers
Chapter 4

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Introduction
• Brain
• Glucose
• Muscles
• Glucose
• Glycogen
• Fat
• Sources of carbohydrates
• “Fattening” – mistaken thinking

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Chemist’s View of
Carbohydrates
• Carbohydrate family
• Atoms and chemical bonds
• Monosaccharides
• Simple carbohydrates
• Glucose, fructose, galactose
• Disaccharides
• Maltose, sucrose, lactose
• Polysaccharides
• Complex carbohydrates

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Atoms and Their Bonds

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Monosaccharides
• Same numbers and kinds of atoms
• Differing sweetness
• Glucose – blood sugar
• Essential energy source
• Part of every disaccharide
• Fructose
• Sweetest of the sugars
• Galactose
• Only in a few foods

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Chemical Structure of Glucose
• On paper, the structure of glucose has to be drawn flat, as it is in the first diagram, but in nature the five
carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and
below the plane.
• In the second diagram, the lines representing some of the bonds and the carbons at the corners are not
shown.
• In the third diagram, the single hydrogens are not shown, but lines still extend upward or downward from
the ring to show where they belong.

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Chemical Structure of the
Monosaccharides

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Disaccharides
• Pairs of three monosaccharides
• Maltose – two glucose units
• Sucrose – glucose and fructose
• Lactose – galactose and glucose
• Condensation
• Links two monosaccharides together
• Hydrolysis
• Breaks a disaccharide in two

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Hydrolysis of a Disaccharide

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Polysaccharides
• Glycogen
• Storage form of energy in the body
• Glucose molecules linked together
in highly branched chains
• Starches
• Storage form of energy in
in plants
• Glucose molecules linked together
in branched or unbranched chains

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Glycogen and Starch
Compared

12. Stepped Art –
Glycogen and Starch Compared
A glycogen molecule contains
hundreds of glucose units in
highly branched chains. Each
new glycogen molecule needs
a special protein (shown here
in red) for the attachment of
the first glucose.
A starch molecule contains hundreds of
glucose molecules in either occasionally
branched chains (amylopectin) or
unbranched chains (amylose).
Starch (amylopectin) Starch (amylose)Glycogen

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Dietary Fibers
• Structural parts of plants
• Differ from starches
• Soluble fibers – benefits
• Insoluble fibers – benefits
• Functional fibers
• Resistant starches
• Phytic acid

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The Bonds of Starch and
Cellulose Compared

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Carbohydrate Digestion
• Ultimate goal
• Glucose for absorption and use
• Hydrolysis via enzymes
• Mouth
• Amylase
• Stomach
• Stomach acid and protein-digesting enzymes
• Role of fiber

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Intestinal Role in Digestion
• Small intestine
• Most carbohydrate digestion occurs here
• Pancreatic amylase
• Specific disaccharide enzymes
• Maltase
• Sucrase
• Lactase
• Large intestine
• Fibers attract water

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Carbohydrate Digestion
in the GI Tract

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Carbohydrate Absorption
• Active transport
• Glucose
• Galactose
• Facilitated diffusion
• Fructose
• Liver
• Conversion of fructose and galactose

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Absorption of
Monosaccharides

20. Stepped Art-
Absorption of monosaccharides
Monosaccharides, the end products
of carbohydrate digestion, enter the
capillaries of the intestinal villi.
In the liver,
galactose and
fructose share
metabolic
pathways with
glucose.
Small intestine
Monosaccharides travel to
the liver via the portal vein.
Glucose is
used by most
cells in the
body.

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Lactose Intolerance
• Lactase activity
• Highest immediately after birth
• Declines with age
• Symptoms of intolerance
• Causes of intolerance beyond age
• Prevalence
• Trait has a genetic component

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Dietary Changes with
Lactose Intolerance
• Manage dairy consumption rather than restrict
• GI bacteria
• Fermented milk products
• Individualized diets
• Potential nutrient deficiencies
• Riboflavin, vitamin D, and calcium

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Lactose in Selected Foods
Foods Lactose (g)
Whole-wheat bread, 1 slice 0.5
Dinner roll, 1 0.5
Cheese, 1 oz
Cheddar or American 0.5
Parmesan or cream 0.8
Doughnut (cake type), 1 1.2
Chocolate candy, 1 oz 2.3
Sherbet, 1 c 4.0
Cottage cheese (low-fat), 1 c 7.5
Ice cream, 1 c 9.0
Milk, 1 c 12.0
Yogurt (low-fat), 1 c 15.0
NOTE: Yogurt is often enriched with nonfat milk solids, which
increase its lactose content to a level higher than milk's.

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Carbohydrate Metabolism
• Glucose is key player
• Storing glucose as glycogen
• Liver storage
• Condensation into glycogen
• Hydrolysis for release of glucose when needed
• Muscle storage
• Hoards glycogen for use during exercise

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Using Glucose for Energy
• Fuels most of body’s cells
• Preferred source for brain, nerve cells, and
developing red blood cells
• Cellular breakdown of glucose
• Making glucose from protein
• Amino acid conversion
• Gluconeogenesis

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Ketone Bodies
• Made from fat fragments
• Inadequate supply of carbohydrates
• Fat metabolism shifts
• Ketone bodies alternative food source during
starvation
• Ketosis disturbs normal acid-base balance
• Carbohydrate needs for protein sparing and
prevention of ketosis
• 50-100 grams/day
• Using glucose to make fat

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The Constancy of Blood
Glucose
• Steady supply in blood stream
• Intestines – food
• Liver – glycogen
• Blood glucose homeostasis
• Insulin
• Moves glucose from blood into cells
• Glucagon and epinephrine
• Brings glucose out from storage

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Maintaining Blood Glucose
Homeostasis

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Balancing Within the
Normal Range
• Balanced meals at regular intervals
• Diabetes
• Insulin either inadequate or ineffective
• Type 1 diabetes
• Type 2 diabetes
• Hypoglycemia
• Prevalence

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Glycemic Response
• Speed of glucose absorption, level of blood
glucose, and return to normal glucose levels
• Low glycemic response
• Desired
• High glycemic response
• Fast absorption, surge in blood glucose, followed
by a plunge below normal glucose levels
• Glycemic index classifies foods
• Limited utility

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Health Effects of Sugars
• Pleasure in moderate amounts
• Obesity and chronic disease
• Nutrient deficiencies
• Energy with few other nutrients
• Discretionary kcalories
• Honey
• More energy per spoonful

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Dental Caries
• Bacteria ferment sugars producing acid
• Erodes tooth enamel
• Food factors associated with tooth decay
• Time of food in mouth
• Sticky foods
• Frequency of sugar consumption
• Food choices
• Factors associated with tooth decay

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Illustration of Dental Caries

34. Stepped Art
Enamel
Caries
Gum
Pulp
(blood
vessels,
nerves)
Bone
Root
canal
Nerve
Blood vessel
Crown
Dentin

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Recommended Intakes of
Sugars
• Dietary Guidelines
• Reduce the intake of kcalories from added sugars
• DRI
• Added sugars
• No more than 25% of day’s total energy
• Impact on other food groups
• WHO and FAO recommendations
• Restrict added sugar consumption to less than
10% of total energy

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Alternative Sweeteners
• Artificial sweeteners
• Non-nutritive sweeteners
• Large doses and adverse effects
• Stevia – herbal product
• Generally recognized as safe
(GRAS)
• Sugar alcohols
• Provide kcalories
• Benefits and side effects

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Health Effects of Starch and
Fibers
• Heart disease
• Whole grains
• Sources
• Soluble fibers
• Sources
• Improving heart disease risk factors
• Diet composition for reducing heart disease risk

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Fibers and Other Health Issues
• Diabetes
• High-fiber foods
• GI health
• High-fiber foods
• Ample fluids
• Weight management
• High-fiber foods and whole grains
• Feeling of fullness

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Fiber and Cancer
• High fiber diet protects against colon cancer
• Fiber supplements
• Food sources of dietary fiber
• Phytochemicals
• Preventing colon cancer
• Diluting, binding, and removing
• Bacterial fermentation

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Harmful Effects of Excessive
Fiber Intake
• Insufficient energy or nutrients
• Abdominal discomfort, gas, diarrhea
• GI obstruction
• Nutrient absorption
• Dietary goals
• Balance, moderation, variety

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Characteristics, Sources, and
Health Effects of Fibers
Major Food Sources Types of Fibers Actions in the Body Probable Health
Benefits
Viscous, Soluble, More Fermentable
• Barley, oats, oat bran, rye.
fruits (apples, citrus),
legumes (especially young
green peas and black-eyed
peas), seaweeds, seeds and
husks, many vegetables,
fibers used as food additives
• Gums
• Pectins
• Psylliuma
• Some
hemicellulose
• Lower blood cholesterol by
binding bile
• Slow glucose absorption
• Slow transit of food through
upper Gl tract
• Hold moisture in stools,
softening them
• Yield small fat molecules after
fermentation that the colon can
use for energy
• Increase satiety
• Lower risk of heart
disease
• Lower risk of diabetes
• Lower risk of colon and
rectal cancer
• Increased satiety, and
may help with weight
management
Nonviscous, Insoluble, Less Fermentable
• Brown rice, fruits, legumes,
seeds, vegetables (cabbage,
carrots, brussels sprouts),
wheat bran, whole grains,
extracted fibers used as food
additives
• Cellulose
• Lianins
• Resistant starch
• Hemicellulose
• Increase fecal weight and
speed fecal passage through
colon
• Provide bulk and feelings of
fullness
• Alleviate constipation
• Lower risk of
diverticulosis,
hemorrhoids, and
appendicitis
• Lower risk of colon and
rectal cancer

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Recommended Intakes of
Starch and Fibers
• DRI for carbohydrates
• 45 to 65 percent of energy requirement
• RDA for carbohydrates
• 130 grams per day
• Fiber
• DV: 11.5 grams per 1000 kcalories
• DRI: 14 grams per 1000 kcalories
• No UL

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Fiber in Selected Foods
Grains
Whole-grain products provide about 1 to 2 g (or more) of fiber per serving:
• 1 slice of whole-wheat, pumpernickel, rye bread
• 1 oz read-to-eat cereal (100% bran cereals contain 10 g or more)
• ½ cooked barley, bulgur, grits, oatmeal
Tips to Increase Fiber Intake
Eat whole-grain breads that contain
≥3 g of fiber per serving.
Eat whole-grain cereals that contain
≥5 g of fiber per serving.
Vegetables
Most vegetables contain about 2 to 3 g of fiber per serving:
• 1 c raw bean sprouts
• ½ c cooked broccoli, brussels sprouts, cabbage, carrots, cauliflower, collards, corn,
eggplant, green beans, green peas, kale, mushrooms, okra, parsnips, potatoes,
pumpkin, spinach, sweet potatoes, swiss chard, winter squash
• ½ c chopped raw carrots, peppers
Tips to Increase Fiber Intake
Eat raw vegetables.
Eat vegetables (such as potatoes and zucchini) with
their skins.
Fruits
Fresh, frozen, and dried fruits have about 2 g of fiber per serving:
• 1 medium apple, banana, kiwi, nectarine, orange, pear
• ½ c applesauce, blackberries, blueberries, raspberries, strawberries
• Fruit juices contain very little fiber
Tips to Increase Fiber Intake
Eat fresh and dried fruit for snacks.
Eat fruits (such as apples and pears) with their skins.
Legumes
Many legumes provide about 6 to 8 g of fiber per serving:
• ½ c cooked baked beans, black beans, black-eyed peas, kidney beans, navy beans,
pinto beans
Some legumes provide about 5 g of fiber per serving:
• ½ c cooked garbanzo beans, great northern beans, lentils, lima beans, split peas
Tips to Increase Fiber Intake
Add legumes to soups, salads, and casseroles.
NOTE: Appendix H provides fiber grams for more than 2000 foods.

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From Guidelines to Groceries
• Grains
• 1 ounce provides about 15g of carbohydrate
• “Three are key” message
• Vegetables
• Corn, peas, and potatoes have higher starch
content
• Fruits
• Milk and milk products
• Protein foods

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Read Food Labels
• Food labels list
• Total carbohydrate
• Starch, fibers, sugars
• Sugars
• Added and natural sugars

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Bread Labels Compared

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Carbs, kCalories,
and
Controversies
Highlight 4

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Carbohydrates’ kCalorie
Contributions
• Obesity and the link to carbohydrates
• Total daily energy intakes have increased
• Activity levels have declined
• Increase in body weight
• Epidemiological studies
• Inverse relationship between carbohydrates and
weight
• Weight loss
• kCalorie intake

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Energy Nutrients over Time

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Daily Energy Intake over Time

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Increases in Adult
Body Weight over Time

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Sugars’ Share in the Problem
• Increase in consumption of added sugars
• High-fructose corn syrup
• Body fat stores
• Carbohydrate cravings
• Self-imposed labeling of foods as good or bad
• Carbohydrate “addiction”
• Not physiological or pharmacological

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Appetite Control
• Fructose and insulin
• Flaws in plausibility
• Food form – liquid or solid
• Beverages can influence weight gains by
providing energy but not satisfying hunger

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Insulin’s Response
• Surge of insulin levels
• How high the surge influences whether body
stores or uses its glucose
• Glycemic effect
• Factors impacting glycemic effect
• Glycemic index and body weight
• Insulin resistance
• Most often caused by being obese
• Body’s insulin response