Transcript Chapter 4 Carbohydrates

Chapter 4:
Carbohydrates,
Sugars, Starches
and Fiber
© 2010 Pearson Education, Inc.
What Are Carbohydrates?
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Produced by plants during photosynthesis
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After eating plant foods, humans convert the carbohydrates
into glucose
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Glucose
• Most abundant carbohydrate
• Preferred source of energy for the blood, brain, and
nervous system
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Carbohydrate-rich plant foods make up the foundation of
diets all over the world
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Classification of Carbohydrates
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Simple carbohydrates
• Monosaccharide
• Disaccharide
• Perceived as sweeter than complex carbohydrates
- Mixes with saliva and reacts with taste buds
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Oligosaccharides
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Complex carbohydrates
• Polysaccharides
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Monosaccharides
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Three nutritionally important monosaccharides
• Glucose
• Fructose
• Galactose
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Monosaccharides
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Glucose
• Blood glucose and blood sugar in the body
• Most abundant monosaccharide in the body
- Is the preferred and main source of energy for the
brain and red blood cells
• Part of every disaccharide
• Only monosaccharide in starches
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Monosaccharides
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Fructose
• Sweetest of natural sugars
• Found abundantly in fruits
• Part of high-fructose corn syrup
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Galactose
• Commonly occurs as part of dissaccharide lactose
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The Structural Differences between Glucose,
Galactose, and Fructose
Figure 4.2
Disaccharides
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Three Disaccharides
• Sucrose
- Most common
• Lactose
• Maltose
- Least common
- Formed from digestion of starches
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Monosaccharides Link to Form Disaccharides
Figure 4.3
Polysaccharides
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Starch
• Plants store glucose in chains of starch
- Amylose
- Straight chain
- More resistant to digestion
- Resistant starch
 May improve health of digestive tract
 May improve glucose tolerance
 May stimulate growth of beneficial intestinal
bacteria
- Amylopectin
- Branched chains
- Easier to digest
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Polysaccharides
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Fiber
• Nondigestible polysaccharides
• Provides no energy
• Classification
- Soluble
- Pectins, beta-glucan, some gums, mucilage
- Easily fermented by intestinal bacteria
• Carbon dioxide, methane, some fatty acids
- Insoluble
- Cellulose, lignin, some hemicelluloses
- Not easily fermented
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Fiber Health Benefits
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Soluble fibers
• Slow gastric emptying and may delay absorption of some
nutrients
- Helps reduce serum cholesterol
- Improve appetite control
- Normalize blood glucose levels
• May help protect against colon cancer
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Insoluble fibers
• Relieves constipation
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Most plant foods contain both soluble and insoluble fibers
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Polysaccharides
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Glycogen
• Storage form of glucose in animals
• Long, branched chains of glucose
• Stored in liver and muscle
• Liver glycogen response to blood glucose (BG) levels
 BG  glycogen breakdown   BG
• Muscle glycogen can be broken down for energy for the
muscle
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The Comparison of Starch and Glycogen Molecules
Figure 4.4
Oligosaccharides
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Similar in length to simple carbohydrates
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Similar in makeup to polysaccharides
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Humans lack the enzymes necessary to digest them
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Intestinal microflora digest and ferment them
• Cause bloating, discomfort, and flatulence
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Food sources
• Legumes, beans, cabbage, brussels sprouts, broccoli
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The Structure of an Oligosaccharide
Figure 4.7
Quick Review
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Complex carbohydrates
• Polysaccharides: starch, fiber, glycogen
• Fiber
- Soluble – fermented by intestinal bacteria; moves
slowly
- Insoluble – moves quickly through and reduces
constipation
- Functional – added to foods
Oligosaccharides
• Contain three to ten units
• Part of cellulose in cell walls
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Carbohydrate Digestion and Absorption
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Disaccharides and starches are digested to monosaccharides
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Monosaccharides are easily absorbed
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Fiber passes through the GI tract undigested
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Figure 4.8a
Figure 4.8b
Figure 4.8c
Figure 4.8d
Absorption of Carbohydrates
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Once digested to monosaccharides
• Absorbed through the intestinal cell mucosa
• Transported to the liver via the portal vein
• Metabolic needs direct fate of the monosaccharides
- Galactose and fructose
• Used by the liver for energy
• Converted to glucose
- Glucose
• Used for energy
• Converted to glycogen through glycogenesis
• Converted to glycerol and fatty acids for storage in
addipocytes
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Glucose Is Stored in the Liver and Muscle
Cells as Glycogen
Figure 4.9
Quick Review
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Digestion of carbohydrates begins in the mouth
Most carbohydrate digestion takes place in the small
intestine
Carbohydrates are broken down to monosaccharides for
absorption
Monosaccharides are converted to glucose in the liver and
• Used as energy
• Stored as glycogen in the liver and muscle cells
• Stored as glycerol and fatty acids in the adipocytes
Fiber travels to the colon undigested and most is eliminated
from the body
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Lactose Intolerance

Deficiency of lactase, the enzyme that digest lactose
• Maldigestion – inability to digest lactose due to low
levels of the enzyme
• Intolerance
- Maldigestion resulting in nausea, cramps, bloating,
flatulence, and diarrhea
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Functions of Carbohydrate
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Provide energy
• 4 kilocalories per gram
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Maintain blood glucose
• Carbohydrate intake
• Glycogenolysis > 4 hours after a meal
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Spare protein
• Prevents the need for glyconogenesis
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Prevents ketosis
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How to Maintain Blood Glucose Levels
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Goal for blood glucose is 70–100 mg/dl
Insulin – lowers blood glucose levels
• Needed for glucose to enter the cell from the blood
stream
- Exception: liver, kidney, and brain cells
• Helps convert glucose to glycogen through glycogenesis
• Helps convert glucose to fatty acids through lipogenesis
• Inhibits lipolysis
Glucagon – increases blood glucose levels
• Stimulates the release of glucose into the blood
• Stimulates glycogenolysis
• Stimulates gluconeogensis
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Insulin and Glucagon Regulate Glucose Metabolism
Figure 4.10
How to Maintain Blood Glucose Levels
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Epinephrine and norepinephrine – increases blood glucose
• Stimulate glycogenolysis and gluconeogenesis
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Cortisol – increases blood glucose
• Stimulates gluconeogensis
• Reduces uptake of glucose by the muscle cells
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Growth hormone – increases blood glucose
• Stimulates fat breakdown for energy
• Reduces uptake of glucose by the muscles
• Increase glucose production in the liver
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Quick Review
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Glucose is the body’s preferred source of energy
• Especially the brain and red blood cells
Adequate carbohydrate intake
• Maintains blood glucose levels
• Spares protein
• Prevents ketosis
Blood glucose levels are maintained by two hormones
• Insulin which lowers blood glucose levels
• Glucagon which raises blood glucose levels
Epinephrine, norepinephrine, corisol, and growth hormone
raise blood glucose levels.
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Glycemic Index
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Classifies the effects of carbohydrate-containing foods on
blood glucose
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May be helpful for diabetics
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Glycemic index (GI) refers to the measured upward rise,
peaks, and falls of blood glucose following consumption of
high-carbohydrate food
• Ranks foods according blood glucose
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Glycemic Load
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Glycemic load (GL) – adjust GI by taking into account the
amount of carbohydrate consumed in a typical serving of
food
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Factors affecting GI
• Ripeness of fruit
• Cooking
• Processing
• Size of food pieces
• Amount of fiber
• Combinations of food eaten
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Glycemic Index and Glycemic Load
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Usefulness of GI and GL for disease prevention and weight
management is controversial
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Is helpful in educating people about
• Carbohydrate content of foods
• Portion sizes
• Serving numbers
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Dietary Fiber
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Benefits
• Helps lower risk of
- Bowel irregularity
- Obesity
- Heart disease
- Cancer
- Diabetes mellitus
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Dietary Fiber
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Chronic constipation can
lead to diverticulosis and
diverticulitis
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Prevention of constipation
and diverticulosis
• Insoluble fiber helps
reduce transit time of
foods in the colon
• Soluble fiber helps make
stool easier to pass by
increasing bulk and
softening texture
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Figure 4.12
Dietary Fiber
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Prevention of heart disease and diabetes
• Viscous, soluble fiber helps lower elevated blood
cholesterol levels
- Interferes with reabsorbtion of bile acid
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Figure 4.13
Dietary Fiber
• Slow moving, viscous, soluble fiber may reduce the rate
which fat and carbohydrate are absorbed
- Decreasing level of fat in blood and improving insulin
sensitivity, decrease risk of heart disease
• Insoluble fiber has been shown to promote heart health
• Viscous soluble fiber helps slow digestion and
absorption helping control blood glucose levels
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Dietary Fiber
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Fiber helps reduce the incidence of several cancers
• Decreases the amount of time cancer-promoting
substances spend in contact with the intestinal lining
• Encourages the growth of colon-friendly bacteria
• Reduces acid in the colon
Helps prevent obesity
• Increase satiety
• Reduce food intake
Caution: Increase dietary fiber and fluid intake
gradually
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Quick Review
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Glycemic index (GI) ranks foods according to effects on
glucose levels compared to white bread or pure glucose
Glycemic load adjust for serving size
Foods that contain high fiber or are eaten with protein and
fat generally have a lower GI.
High-fiber diet health benefits include reduced risk of
• Constipation
• Diverticulosis
• Heart disease
• Obesity
• Diabetes Mellitus
• Cancer
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Importance of Whole Grains
Carbohydrate Sources
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Best choices should include nutrient-dense, low-saturated
fat foods, simple carbohydrates, fiber, complex
carbohydrates
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Food Sources of Carbohydrates
Figure 4.14
Food Sources of Fiber
Figure 4.15
Quick Review
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Best sources of carbohydrates are
• Fresh fruits and vegetables • Legumes
• Whole grains
• Low-fat dairy products
Excellent sources of fiber are
• Whole grains
• Legumes
• Fruits
• Nuts
• Seeds
• Vegetables
Packaged foods can be good sources of starch and fiber
• Read label carefully
• Avoid too much sugar, fat, and kilocalories
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Diabetes Mellitus
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Occurs when an individual either doesn’t make enough, or
is unable to utilize, the hormone insulin to regulate blood
glucose levels
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Epidemic
• Sixth leading cause of death in the United States
• Costs the U.S. almost $100 billion annually
• Number of people with diabetes is rising annually
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Diabetes Mellitus
Consume
Carbohydrates
Blood Glucose
Rises
Blood Glucose
Rises
Liver Breaks
Down Glycogen
and Produces
Glucose from
NonCarbohydrate
Sources
Ketoadicosis
No Insulin
Available or
Cells
Resistant
Cell
Starves
Body
Uses Fat
for Fuel
Forms of Diabetes
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Type 1
• Usually begins in childhood or early adulthood
• 5–10% of diabetics
• Immune system destroys beta cells of the pancreas
- No insulin produced
• Common symptoms of elevated blood sugar
- Polydipsia
- Polyuria
- Polyphagia
• Require insulin and frequent blood glucose monitoring
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Forms of Diabetes
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Type 2
• Overweight individuals develop this form frequently
• 90–95% of diabetics
• Can go undiagnosed
- Damages vital organs without individual being aware
of it
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Polycystic ovary syndrome
• Hormonal imbalance in women
• Have higher incidence of insulin resistance and
hyperinsulinemia
- Increased risk of developing type 2 diabetes
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Forms of Diabetes
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Prediabetes
• Impaired glucose tolerance
• Fasting blood sugar between 100 mg/dl and 126 mg/dl
• High risk of developing diabetes and heart disease
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Diabetes
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Long-term damage from diabetes
• Nerve damage
• Tooth loss
• Leg and foot amputations • Gum problems
• Kidney disease
• Eye diseases
• Heart disease
• Blindness
Slowing of onset of complications
• Control level of blood glucose through
- Diet
- Insulin or oral medication
- Monitoring blood glucose
- Regular healthcare visits
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Diabetes
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Slowing of onset of complications
• Control level of blood glucose through
- Diet
- Insulin or oral medication
- Monitoring blood glucose
- Regular health care visits
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Quick Review
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Diabetes involves inadequate regulation of blood glucose
levels
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Type 1 diabetes – inadequate production of insulin
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Type 2 diabetes – insulin resistance
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Chronic high blood glucose can damage vital organs
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Diabetics need medications and/or insulin to manage blood
glucose
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High-fiber diet and routine exercise play a key role in
managing and preventing diabetes
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Polycystic ovary syndrome increases the risk of developing
type 2 diabetes
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Hypoglycemia
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A blood glucose level that is too low (usually below
70 mg/dl)
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Signs and symptoms
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• Hunger
• Confused
• Nervousness
• Weak
• Dizziness
• Shaky
• Light-headed
• Sweaty
Eating or drinking carbohydrate rich foods
• Relieves symptoms
• Raises blood glucose
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Change in Blood Glucose After Eating a
High-Carbohydrate Meal
Figure 4.17
Fasting Hypoglycemia
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Occurs in the morning after an overnight fast
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Occurs during long stretches between meals or after
exercise
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May be caused by
• Medications
• Illness
• Drinking too much alcohol
• Certain tumors
• Hormone imbalances
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Quick Review
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Symptoms of hypoglycemia
• Hungry, nervous, light-headed, shaky, and/or sweaty
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Diabetics who take medications and/or insulin and do not
eat properly are at risk
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Individuals without diabetes may experience reactive
hypoglycemia several hours after meals
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Fasting hypoglycemia may occur upon awaking in the
morning
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Can be caused by medications, illnesses, hormone
imbalances, or excessive consumption of alcohol
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Natural versus Added Sugar
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Naturally occurring sugar
• Sugars such as fructose and lactose found naturally in
foods
• Tend to be nutrient dense
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Added sugar
• Sugars added to processed foods and sweets
• Empty calories
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Slices of an Orange versus Orange Slices
Figure 4.18
Added Sugar
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Reasons sugar is added to foods
• To keep product moist
• To turn pastries a golden brown
• Preservative
• Thickening agent
• Make yeast rise
• Make foods taste sweet
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Finding Added Sugars on the Label
Figure 4.19
Americans Drink the Majority of Their Sugar
Figure 4.20
Health Effects of Sugar
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Sugar can contribute to
• Dental carries
• Elevated level of fat in the blood
• Lowing of HDL cholesterol
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Sugar does not cause
• Increased risk of diabetes
• Hyperactivity in children
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Sugar is not considered an addictive substance
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Quick Review
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Taste buds do not distinguish between naturally occurring
sugar and added sugar
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Foods with naturally occurring sugar provide more
nutrition and satiation than empty-calorie sweets
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There are numerous names for added sugar
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Soft drinks are the number-one contributor of added sugars
to U.S. diets
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Putting It All Together
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Carbohydrates are an important part of a healthy diet
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Whole grains, fruits, vegetables, and lean dairy products
• Provide carbohydrates and vitamins and minerals
• Should be the predominant source of carbohydrates
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Whole grains, fruits, and vegetables are a good source of
fiber and phytochemicals
• Adequate amounts of these can prevent many chronic
disease
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Sugary foods should be eaten in moderation
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