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Chapter 4: Carbohydrates: Sugar,
Starch, Glycogen and Fiber
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Carbohydrates (CHO)—composed of carbon,
hydrogen and oxygen; two types, simple and
complex.
Simple carbohydrates
◦ Sugar is a simple CHO—CHO composed of single
and linked sugars (mono and disaccharides)
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Complex carbohydrates
◦ Starch and fiber
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The three single sugars (monosaccharides) are
◦ Glucose
◦ Fructose
◦ Galactose
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The three double sugars (disaccharides)
◦ Lactose
 It is made of glucose linked to galactose
◦ Maltose
 It is made of two glucose units
◦ Sucrose
 It is made of glucose linked to fructose
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Starch—long chains of glucose units found in plants.
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Glycogen-the storage form of CHO found in animals.
Soluble fibers dissolve in water
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Form gels (are viscous)
Easily digested by bacteria in the human colon
Found in barley, legumes, fruits, oats, vegetables
Are associated with a lower risk of chronic disease
Add a pleasing consistency to foods
Insoluble fibers do not dissolve in water
• Are less easily fermented
• The outer layers of whole grains, the strings of celery,
etc. contain insoluble fibers such as cellulose and
hemicellulose
• These fibers retain their structure and texture even after
hours of cooking
• They aid the digestive system and ease elimination
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Human digestive enzymes cannot break the
bonds between the sugar units of starch
◦ Thus, most fibers pass through the human body
without providing energy
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Bacteria within the human large intestine
can digest fibers to varying degrees by
fermenting them
◦ This produces gas in many people
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DRI recommendations
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WHO recommendation
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Recommendations and Intakes
◦ 2000 calorie diet with 225-325 grams of carbohydrate per day
◦ 2000 calorie diet with 275-375 grams of carbohydrate
◦ DRI recommendations for fiber:
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Men, age 19-50: 38 g/day
Men, age 51+: 30 g/day
Women age 19-50: 25 g/day
Women age 51+: 21 g/day
Children, age + 5 grams (ADA recommendation)
The ADA recommends 20 to 35 grams of total fiber per
day
 This is about 2x higher than the average intake
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The DRI committee recommends that 45% - 65%
of daily calories come from carbohydrates
Fats are not normally used as fuel by the brain
and central nervous system
◦ Glucose is the primary energy source for nerve cells
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Gram for gram carbohydrates contain fewer
calories (4) than do dietary fats (9)
Converting glucose into fat is metabolically costly
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Benefits of fiber include:
◦ Promotion of normal blood cholesterol
concentrations
◦ Modulation of blood glucose concentrations
◦ Maintenance of healthy bowel functions
◦ Help in the maintenance of a healthy body weight
◦ Help to avoid insulin spiking
◦ Increase satiety
◦ ….and more
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Lower Cholesterol and Heart Disease Risk
◦ Diets rich in complex carbohydrates may protect
against heart disease
 Such diets are usually:
 low in saturated fat, trans fat, and cholesterol
 High in fibers, vegetable proteins, and phytochemicals
How fiber reduces
cholesterol levels
•Foods rich in viscous
fibers lower blood
cholesterol by binding with
cholesterol-containing bile
and carrying it out with the
feces
•Bile is needed for
digestion, so the liver
responds to its loss by
drawing on the body’s
cholesterol to make more
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Blood Glucose Control
◦ Viscous fibers trap nutrients and delay transit
through the digestive tract
 As a result glucose absorption slows and this helps
maintain steady levels of blood glucose and insulin
 Large fluctuations in blood glucose and insulin are
thought to be associated with the onset of the most
common form of diabetes
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In people with diabetes, high-fiber foods play a
role in modulating blood glucose and insulin levels
◦ Lowering the likelihood of medical complications
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Healthy Weight Management
◦ Foods rich in complex carbohydrates tend to be low
in fats and added sugars
 They, therefore, promote weight loss by providing less
energy
 Fibers also create feelings of fullness and delay hunger
because they swell as they absorb water
◦ Buying such pure fiber compounds is neither
necessary nor advisable
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Maintenance of Digestive Tract Health
◦ Fiber, along with fluid intake, play a role in
maintaining proper colon function
 Fibers such as cellulose enlarge and soften stools
 Speeding their passage through the intestine and making
for easier elimination
 These fibers help alleviate or prevent constipation
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Constipation is difficult, incomplete, or
infrequent bowel movements
◦ Associated with discomfort in passing dry,
hardened feces
◦ Large, soft stools ease the task of elimination for
the rectal muscles
 Making it less likely that the rectal veins will swell
(hemorrhoids)
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Fiber prevents compaction of intestinal
contents
◦ Such compaction could obstruct the appendix and
permit bacteria to invade and infect it (appendicitis)
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Fiber stimulates the GI tract muscles so they
retain their strength and resist bulging out
into pouches (diverticula)
◦ Diverticulitis is the inflammation of diverticula
Diverticulosis/
Diverticulitis
diverticula
colon
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High-fiber diets lower the rates of colon cancer
◦ Nutrient & phytochemical content of fiber-rich foods
◦ Fibers dilutes & helps remove of cancer-causing
agents from the colon
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Lowering the pH of intestinal contents
◦ Contributing to the destruction of cancer cells and
slowing cancer cell replication
◦ To obtain glucose from food the digestive system
must first break down carbohydrates in the food
into monosaccharides that can be absorbed
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Starts in the Mouth: Starch
◦ Starch digestion begins in the mouth
 An enzyme in saliva splits starch into maltose
 This enzyme continues to act on starch while it remains in
the stomach’s upper storage area
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In the stomach, CHO mixes with acid and salivary
enzymes are deactivated
Starch digestion resumes in the small intestine
◦ Where a starch-splitting enzyme produced by the
pancreas acts
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Digestible carbohydrates are ultimately split into
monosaccharides before they are absorbed
 Disaccharides and small polysaccharides are split by
enzymes attached to the cells lining the small intestine
Digestion of
Carbohydrates
esophagus
liver
pancreas
stomach
small intestine
large intestine
(colon)
1 Fiber, starch, monosaccharides, and disaccharides enter the
stomach and pass into the small intestine. Some of the starch is
partially broken down by an enzyme from the salivary glands before it
reaches the small intestine.
esophagus
liver
pancreas
stomach
small intestine
large intestine
(colon)
2 An enzyme from the pancreas
digests most of the starch to
disaccharides.
intestine
wall cells capillary
esophagus
liver
pancreas
stomach
small intestine
large intestine
(colon)
intestine
wall cells capillary
3 Enzymes on the
surface of intestinal
wall cells split
disaccharides to
monosaccharides.
esophagus
liver
pancreas
stomach
small intestine
large intestine
(colon)
intestine
wall cells capillary
4
Monosaccharides
enter capillaries,
then are
delivered
to the liver via the
portal vein.
esophagus
liver
pancreas
stomach
small intestine
large intestine
(colon)
intestine
wall cells capillary
5 The liver converts
galactose and
fructose to glucose.
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As blood glucose rises, the pancreas releases
insulin
◦ Insulin signals the body’s tissues to take up glucose
 2/3 of total glycogen is stored in & used by muscle
 A small emergency store is found in the brain
 The remainder is stored in the liver, which makes it
available to the body as blood glucose
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When blood glucose concentration drops the
pancreas produces glucagon
◦ Enzymes in the liver break down glycogen releasing
it into the blood as glucose
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Epinephrine also breaks down liver glycogen
as part of the body’s defense mechanism in
times of danger
◦ To a person living long ago, this internal source of
quick energy was indispensable to a life filled with
physical peril
◦ This quick-energy response to stress also works to
our advantage today
 To meet emergencies, we are advised to eat and store
carbohydrates at regularly timed meals
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Diabetes mellitus
◦ A disease characterized by high blood glucose levels
and inadequate or ineffective insulin
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The prevalence of diabetes is increasing
◦ Leading cause of blindness in the US
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Additional complications include:
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Amputations
Complications in pregnancy
Heart disease
Kidney disease
Premature death
Increased risk of death from flu or pneumonia
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Type 1 Diabetes
◦ Little or no pancreatic secretion of insulin
◦ Often diagnosed in childhood
◦ Less common (up to 20% of cases)
 Most common chronic disease among children and young
adults
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Type 1 diabetes is the result of a person’s
immune system attacking the insulin-making
cells of the pancreas
◦ An immune system attack on the pancreas may be
provoked by
 Genetics, viral infection and other diseases, toxins,
allergens, disordered immune system
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Type 2 Diabetes
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Pancreas makes sufficient insulin
Body’s cells resist insulin’s action
Often diagnosed in adulthood
Incidence has increased by over 60% since 1991
Characterized by insulin resistance
◦ A condition in which insulin is less then effective in
moving glucose from the bloodstream into the cells
◦ As blood glucose rises, so does blood insulin
 Eventually, the pancreas is unable to make insulin
 With age, people may require insulin to supplement their own
supply
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Type 2 Diabetes and the Genes
◦ Genetic component to Type 2 susceptibility
 Genes are not destiny
 Genetic factors may increase a person’s risk by ≈30%
 Diet and exercise play a major role
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Prevention is likely when individuals control
lifestyle
◦ Men and women can reduce their risk if they:
 Maintain a healthy body weight
 Consume a diet high in vegetables, fruit, fish, poultry,
and whole grains
 Exercise regularly
 Restrict alcohol
 Don’t smoke
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Half of those with diabetes are unaware of
their condition
◦ And therefore fail to take action to prevent its
damage
◦ Early stages often present few or no warning signs
◦ Recommendations call for everyone over 45 years
old (40 in Canada) and younger people with risk
factors, such as obesity, to be tested regularly
Warning Signs of Diabetes
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Type 1 and Type 2 are the most common
forms of diabetes
◦ Both are disorders of blood glucose regulation
Comparison of Type 1 & Type 2 Diabetes
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Managing Diabetes
◦ Optimal diet:
Is adequate in nutrients
Provides the recommended amount of fiber
Is moderate in added sugars
Provides a controlled amount of total carbohydrates
Is low in saturated fat and may provide some
monounsaturated fat
 Is adequate but not too high in protein
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The Glycemic Response
◦ The glycemic index (GI) is a measure of the ability
of a food to elevate blood glucose and insulin levels
 Scores are compared with a standard, usually white
bread or glucose
 A food’s score depends on several factors
 For example, ice cream, a high-sugar food, ranks lower
than baked potatoes, a high-starch food
Glycemic Index
The GI of foods is affected by:
•Individual differences among people
•Ripeness of fruits/vegetables
•Other foods consumed at the same time
Who might find this information
helpful for making dietary choices?
•People with Diabetes
•Those dieting
•Athletes
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Hypoglycemia
◦ Blood glucose concentrations below normal
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Symptoms include:
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Fatigue & Weakness
Dizziness & Trembling
Irritability
Rapid heartbeat
Anxiety
Sweating
Hunger
Headaches
Confusion
Impairment of intellectual tasks