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C HAPTER
4
Carbohydrates:
Plant-Derived Energy
Nutrients
PowerPoint® Lecture Slides prepared by
James Bailey, University of Tennessee
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings.
What Are Carbohydrates?
Carbohydrates
 One of the three macronutrients
 A primary energy source, especially for nerve and
red blood cells
 Composed of carbon, hydrogen, oxygen
 Good sources include fruits and vegetables, grains,
roots and tubers
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What Are Carbohydrates?
Glucose
 Produced by plants through photosynthesis
 Found in plants as a component of disaccharides
and complex carbohydrates
 Principle form of carbohydrate found in blood 
blood sugar is glucose
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Photosynthesis
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Figure 4.1
What Are Carbohydrates?
Simple carbohydrates contain one or two molecules.
 Monosaccharides contain only one molecule
 Glucose, fructose, galactose
 Disaccharides contain two molecules
 Lactose, maltose, sucrose
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Monosaccharides
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Figure 4.2
Disaccharides
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Figure 4.3
What Are Carbohydrates?
Complex carbohydrates




Long chains of glucose molecules
Hundreds to thousands of molecules long
Also called polysaccharides
Starch, glycogen, most fibers
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Complex Carbohydrates
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Figure 4.4
Complex Carbohydrates
Starch
 Plants store carbohydrates as starch
 We digest (break down) starch to glucose
 Grains, legumes, and tubers are good sources of
starch in our diet
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Complex Carbohydrates
Glycogen
 Animals store some (not a lot) carbohydrate as
glycogen
 Stored in the liver and muscles
 Not found in food and therefore not a source of
dietary carbohydrate
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Complex Carbohydrates
Fiber
 Dietary fiber: the non-digestible part of plants
 Grains, rice, seeds, legumes, fruits
 Functional fiber: carbohydrate extracted from
plants and added to food that have known health
benefits
 Cellulose, guar gum, pectin, psyllium
 Total fiber = dietary + functional fiber
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Complex Carbohydrates
Dietary fiber is also classified by solubility.
Soluble fiber
 Dissolves in water
 Easily digested by bacteria in the colon  acts as
fuel for healthy gut bacteria
 Found in citrus fruits, berries, beans and oats
 Reduces risk for CVD and type 2 diabetes by
lowering blood cholesterol and glucose levels
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Complex Carbohydrates
Insoluble fibers
 Generally do not dissolve in water
 Promote regular bowel movements
 Found in wheat bran, the husk of grains, and many
vegetables
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Digestion of Carbohydrates
Salivary amylase
 Begins the process of breaking starch down to
maltose
 The acidic environment found in the stomach
inactivates this enzyme
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Digestion of Carbohydrates
Most chemical digestion of carbohydrates occurs in
the small intestine.
Pancreatic amylase
 Enzyme produced in the pancreas and secreted into
the small intestine
 Enzymatically digests starch to maltose
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Digestion of Carbohydrates
 Additional enzymes secreted by cells that line the
small intestine (mucosal cells) digest disaccharides
to monosaccharides
 These enzymes include maltase, sucrase, and
lactase
 Monosaccharides are absorbed into the cells lining
the small intestine and then enter the bloodstream
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Digestion of Carbohydrates
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Figure 4.8
Digestion of Carbohydrates
 All monosaccharides are converted to glucose by
the liver
 Glucose circulating in the blood is our primary
energy source
 Excess glucose is converted to glycogen by the
liver and muscle
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Storage of Glycogen
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Figure 4.9
Digestion of Carbohydrates
 Humans do not have the enzymes necessary to
digest fiber
 Bacteria in the large intestine can break down some
fiber
 Most fiber remains undigested and is eliminated
with feces
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Regulation of Blood Glucose
The level of glucose in the blood is closely regulated
in a relatively narrow range.
Two hormones, insulin and glucagon, control the
level of glucose in the blood.
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Regulation of Blood Glucose: Insulin
Insulin
 Produced by beta cells of the pancreas
 Helps transport glucose from the blood into cells
 Stimulates the liver to take up glucose and convert
it to glycogen
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Regulation of Blood Glucose: Insulin
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Figure 4.10a
Regulation of Blood Glucose: Glucagon
Glucagon
 Produced by alpha cells of the pancreas
 Stimulates the breakdown of glycogen to glucose to
make glucose available to cells of the body
 Stimulates gluconeogenesis—the production of
“new” glucose from amino acids
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Regulation of Blood Glucose: Glucagon
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Figure 4.10b
Regulation of Blood Glucose
Glycemic index
 A food’s ability to raise blood glucose levels
 Foods with a low glycemic index:
 Moderate fluctuations in blood glucose level
 Are better for all people, and particularly important for
people with type 2 diabetes/ insulin resistance
 Often are higher in fiber
 May reduce the risk of heart disease, colon, and
prostate cancer
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The Role of Carbohydrates
Energy
 Each gram of carbohydrate = 4 kcal or 17 kJ
 Red blood cells rely only on glucose for their
energy supply
 Both carbohydrates and fats supply energy for daily
activities
 Glucose is especially important for energy during
exercise
 During intense exercise carbohydrate will supply
2/3 or more of the total energy needed
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The Role of Carbohydrates
Energy
 Sufficient energy intake from carbohydrates
prevents production of ketones as an alternate
energy source
 Excessive ketones can result in high blood acidity
and ketoacidosis
 High blood acidity damages body tissues
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The Role of Carbohydrates
Fiber




May reduce the risk of colon cancer
May reduce the risk of heart disease
May enhance weight loss
Help prevents hemorrhoids, constipation, and
diverticulosis
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How Much Carbohydrate?
 Recommended Dietary Allowance (RDA) is 130
g/day just to supply the brain with glucose
 45–65% of daily calorie intake should be in the
form of carbohydrates
 Focus on foods high in fiber and low in added
sugars
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Simple versus Complex Carbohydrates
Diets high in simple sugars
 Can cause dental problems such as cavities and
gum disease
 Are associated with increased levels of “bad
cholesterol”
 Are associated with decreased levels of “good
cholesterol”
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Simple versus Complex Carbohydrates
The Adequate Intake (AI) of fiber is 14 grams for
every 1,000 kcal in the diet (25 g for women and 38
g per day for men.
Most Americans eat only half the recommended
amounts of fiber.
Whole-grain foods are a more healthful choice than
foods with added sugar or fiber.
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Alternative Sweeteners
Nutritive sweeteners
 Contain 4 kcal energy per gram
 Sucrose, fructose, honey, brown sugar
Sugar alcohols
 Contain 2–4 kcal energy per gram
 Do not support bacterial growth in the mouth
Non-nutritive (alternative) sweeteners
 Provide little or no energy
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The book covers artificial sweeteners…
But, your instructor, Sara Ducey, does not support
their use. Ask her questions during the week she is
on site.
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Alternative Sweeteners
Acceptable Daily Intakes (ADI) have been
established for
 aspartame
 sucralose
 acesulfame-K
No ADI has been set for saccharin but it has been
removed from the list of cancer-causing agents.
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Alternative Sweeteners
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Figure 4.17
Health Disorders
Three health disorders related to carbohydrate
metabolism are
 Diabetes
 Hypoglycemia
 Lactose intolerance
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Diabetes
Diabetes
 Inability to regulate blood glucose levels
 Three types
 Type 1 diabetes
 Type 2 diabetes
 Gestational diabetes
 Untreated diabetes can cause nerve damage, kidney
damage, blindness, and can be fatal
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Symptoms of Diabetes
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Table 4.5
Diabetes
Type 1 diabetes
 Accounts for <10% of all cases
 Patients do not produce enough insulin, so must
bring it into the body with insulin injections.
 Causes hyperglycemia—high blood sugar (glucose)
because there is no insulin to help sugar enter cells.
 May be the result of an autoimmune disease
 Most frequently diagnosed in adolescents
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Diabetes
Type 2 diabetes
 Most diabetics (>90%) have type 2 diabetes
 Body cells are insensitive or unresponsive to
insulin – also called insulin resistance
 Excess insulin is often produced – resulting in high
blood sugar + high blood insulin
 Causes hyperglycemia because cell receptors do not
respond to the insulin, and cannot transport glucose
from the blood into the cells
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Diabetes
Type 2 diabetes (continued)
 Cause is unclear but genetics, obesity, and physical
inactivity play a role
 Treated with diet, exercise, and possibly oral
medications
 Healthy lifestyle choices may prevent or delay
onset of type 2 diabetes
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Hypoglycemia
Hypoglycemia
 Low blood sugar (glucose)
 Reactive hypoglycemia results when too much
insulin is produced after a meal
 Causes shakiness, sweating, anxiety
 Fasting hypoglycemia results when too much
insulin is produced even when the patient has not
eaten
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Lactose Intolerance
Lactose intolerance
 Insufficient lactase production causes an inability to
digest the disaccharide lactose found in dairy
products
 Symptoms include intestinal gas, bloating, nausea,
cramping, diarrhea
 Lactose intolerant people may need to find alternate
sources of calcium, riboflavin and protein.
 Specially formulated milk products or oral
consumption of the lactase enzyme can be used to
treat lactose intolerance
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