Download Carbohydrates

Chapter 4
Carbohydrates: Sugars,
Starches, and Fiber
4-2
•
http://www.youtube.com/watch?v=dBnniua6-oM
• www.sugarstacks.com
Learning Objectives
• Discuss the difference between refined
and unrefined carbohydrates.
• Compare the structure of simple and
complex carbohydrates.
• Distinguish between soluble and insoluble
fiber and name food sources of each.
• Define lactose intolerance and explain its
cause.
4-3
Learning Objectives
• Discuss the effects of dietary fiber on
gastrointestinal function and health.
• Describe the steps involved in
metabolizing glucose to produce energy.
• Explain how the hormones insulin and
glucagon are involved in regulating blood
glucose levels.
4-4
Learning Objectives
• Compare the causes and consequences
of type 1 and type 2 diabetes.
• Discuss the health risks and benefits
associated with carbohydrates.
• Discuss artificial sweeteners.
4-5
What do you know already?
Macronutrients: Our Main Questions
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What are they?
What do they do in us?
Where do they come from?
Structure
Digestion
Metabolism and Storage
Recommended Allowances
Consequences of too much
Consequences of too little
Other Issues (substitutes, etc.)
Sugars: What They
Are?
• White sugar (sucrose)
• High-fructose corn syrup or
corn syrup
• Sorbitol
• Brown sugar
• Molasses
• Honey
• Powdered sugar
• Raw sugar
• Fiber
•
http://www.sugar.org/consumers/sweet_by
_nature.asp?id=275
Sugars: What
They Do In Us.
• Carbohydrates meet
your body’s energy needs
– Feed your brain and
nervous system
– Keep your digestive system fit
– Within calorie limits, help keep your body lean
– Together with fats and protein, digestible
carbohydrates add bulk to foods
– Indigestible carbohydrates yield little or no
energy but provide other benefits
– DNA backbone
Carbohydrates: Where
do they come from?
• Carbohydrate-rich foods
come almost exclusively
from plants
– Milk is the only animalderived food that contains
significant amounts of
carbohydrate
Carbohydrates: Where do they
come from? Synthesis of
Glucose and Starch
4-16
Carbohydrates (CH2O)n
• Simple carbohydrates
(sugars)
– Monosaccharides
– Disaccharides
• Complex carbohydrates
(polysaccharides)
– Glycogen
– Starch
– Fiber
Simple
Carbohydrates
• Monosaccharides
– C6H12O6
• Glucose
• Fructose
• Galactose
Simple Carbohydrates:
The Monosaccharides
1. Glucose C6H12O6
• The essential energy source
for all body functions.
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Other names: Dextrose and
Blood Sugar.
A component of each
disaccharide.
The body’s main source of
energy.
Simple Carbohydrates:
The Monosaccharides
• Fructose:
• The sweetest of all sugars
– (1.5 X sweeter than sucrose)
• Occurs naturally in fruits and
honey
– “the fruit sugar”
Simple Carbohydrates:
The Monosaccharides
• Galactose
– Seldom occurs freely in
nature
– Binds with glucose to form sugar in milk:
lactose.
– Once absorbed by the body, galactose is
converted to glucose to provide energy.
Monosaccharides to
Polysaccharides
• Monosaccharides can be joined to make
disaccharides and polysaccharides.
– Via condensation reactions
• Polysaccharides can be broken down to
monosaccharides.
– Via hydrolysis reactions
Condensation
Think of clay, if you take water out, it becomes hard
Hydrolysis
If you put water into something, it breaks it apart
Disaccharides
• Maltose
• Sucrose
• Lactose
Simple
Carbohydrates:
The Disaccharides
Maltose
Maltose = Glucose + Glucose
• Produced when starch breaks down.
• Used naturally in fermentation reactions of
alcohol and beer manufacturing.
• Aromatic in baking
Simple
Carbohydrates:
The Disaccharides
Sucrose
Sucrose = Glucose + Fructose
*Table sugar
*Found naturally in plants: sugar cane,
sugar beets, honey, maple syrup
*Sucrose may be purified from plant
sources into Brown, White and
Powdered Sugars.
Simple Carbohydrates:
The Disaccharides
Lactose
Lactose = Glucose + Galactose
• The primary sugar in milk and milk
products.
• Many people have problems digesting
large amounts of lactose (lactose
intolerance)
Carbohydrates (CH2O)n
• Simple carbohydrates
(sugars)
– Monosaccharides
– Disaccharides
• Complex carbohydrates
(polysaccharides)
– Glycogen
– Starch
– Fiber
The Complex Carbohydrates:
• Polysaccharides: containing 2 or more
monosaccharides attached together
Three types are important in nutrition:
1. Glycogen- digestible
2. Starch- digestible
3. Fiber- indigestible
The Complex
Carbohydrates:
Glycogen
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The storage form of glucose in the body.
Stored in the liver and muscles.
Found in tiny amounts in meat sources.
Not found in plants.
Not a significant food source of carbohydrate.
The Complex Carbohydrates:
Starch
• The major digestible polysaccharide in our
diet.
• Sources: Wheat, rice, corn, rye, barley,
potatoes, tubers, yams, etc.
• Two types of plant starch: 1. Amylose
2. Amylopectin
The Complex
Carbohydrates
Fiber
Indigestible polysaccharides
Types of fiber:
1. Soluble (dissolve in water)- gums,
pectins, mucilages, some hemicellulose
2. Insoluble (do not dissolve in water)cellulose, lignin, many hemicelluloses
Food Sources of Fiber
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Soluble fiber
1.
2.
3.
4.
Fruits
Legumes
Oats, barley, and rye
Also seeds and
vegetables
•
Insoluble fiber
1. Wheat bran, brown
rice, whole grains
2. Vegetables
(cabbage, carrots)
3. Fruits
4. Legumes
Food Sources of Fiber
•
Soluble fiber
1.
2.
3.
4.
Fruits
Legumes
Oats, barley, and rye
Also seeds and
vegetables
•
Insoluble fiber
1. Wheat bran, brown
rice, whole grains
2. Vegetables
(cabbage, carrots)
3. Fruits
4. Legumes
Health Effects of Fiber
• Soluble, viscous
fiber
– Lowers risk of heart
disease & stroke by:
•
Binding bile
– Lowers risk of
diabetes and controls
diabetes by:
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Slowing glucose
absorption
– Also holds moisture
in stools, softening
them
• Insoluble,
nonviscous fiber
– Alleviates
constipation and
lowers risk of
hemorrhoids and
diverticulosis by:
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Increasing fecal weight
and speeding fecal
passage through the
colon
– May help with weight
management
Carbohydrate
Digestion in
the GI Tract
• Simple
• Starch
• Fiber
Simple sugars: Monosaccharides
• Simple sugars are simply absorbed
without digestion
Carbohydrates in the Digestive Tract
• Disaccharides
and complex
carbohydrates
must be digested
for monosaccharides to be
absorbed.
• Digestible vs.
Indigestible
carbohydrates
4-19
Lactose Intolerance
• Not enough enzyme lactase in the small
intestine to digest the milk sugar lactose
• Symptoms: intestinal gas and bloating,
diarrhea
• More common in Asian, Native American,
and Mediterranean populations
• What are alternative means to meet
calcium needs for lactose-tolerant
populations?
4-20
Starch
Fiber
Indigestible Carbohydrates
• Fiber, some
oligosaccharides,
and resistant starch
• Health implications
– Stimulate GI motility
– Promote a healthy
microflora
– Slow nutrient absorption
– Increase intestinal gas
4-21
Soluble Fiber—Healthy Heart
• Dissolves in water or
absorbs water
• Can be broken down by
the intestinal microflora
• Includes: pectins, gums,
semicelluloses
• Food sources: oats,
apples, beans, seaweeds
• Health benefits: lower
blood cholesterol
4-34
Insoluble Fiber—Happy GI Tract
• Does not dissolve in water
• Cannot be broken down by
bacteria in the large intestine
• Includes: cellulose,
hemicellulose, and lignin
• Food sources: wheat bran,
rye bran, and vegetables
• Health benefits: soften stools
and decrease transit time
4-35
Indigestible Carbohydrates and
the Risk of Colon Cancer
• Epidemiologic studies: the incidence of
colon cancer is lower in populations
consuming diets high in fiber
• Recent intervention studies: not supportive
of the epidemiologic observations
• The scientific consensus: enough
evidence that diets high in fiber protect
against colon cancer
4-36
Carbohydrate Metabolism
• Storing glucose
as glycogen
• Using glucose
for energy
How Glucose is Stored/Used:
Getting Glucose Into Cells.
Constancy of Blood Glucose
• Diabetes
– Type 1
diabetes
• Failure of
insulin
production
– Type 2
diabetes
• Obesity
Abnormal
Blood Glucose
Levels in
Diabetes
Mellitus
4-28
Diabetes Mellitus: Symptoms
• Immediate Symptoms
– Excessive thirst, frequent urination, blurred
vision, and weight loss
• Long-term complications
– Damage to the heart, blood vessels, kidneys,
eyes, and nerves
4-29
Diabetes Mellitus: Treatment
• Diet
– Carbohydrate intake should be distributed
through the day to control blood glucose
levels,
– Exchanging lists or other carbohydratecounting tools is useful
• Exercise
– Increase sensitivities of body cells to insulin
• Medication
• Insulin injection for Type 1
• Insulin can help for some Type 2 patients
4-30
Carbohydrate Metabolism
• Making glucose from protein
– Gluconeogenesis
– Protein-sparing
action of
carbohydrates
Carbohydrate Metabolism
• Making glucose from protein
– Gluconeogenesis
– Protein-sparing
action of
carbohydrates
Carbohydrate Metabolism
Carbohydrate Metabolism
• Converting glucose to fat
– Energetically expensive
• The conversion of excess
glucose to fat requires
many steps and costs a
great deal of energy
– When presented with both
glucose and fat, the body prefers to
store the fat and use the glucose to
meet immediate energy needs
• This maximizes energy storage
Carbohydrate Metabolism
• When
presented
with both
glucose and
fat, the body
prefers to
store the fat
and use the
glucose to
meet
immediate
energy needs
Use the glucose and store the fat
Gluconeogenesis
• Making
glucose
from
protein
4-23
Carbohydrates are Needed to
Break Down Fat
4-24
Constancy of
Blood Glucose
• Hypoglycemia
– Rare in
healthy
people
http://en.wikipedia.org/wiki
/Hypoglycemia
Hypoglycemia: Low Blood Glucose
• Can occur in people with diabetes as a
result of over-medication or imbalance
between insulin level and carbohydrate
intake
• Can result from abnormalities in the
production or response to insulin or other
hormones involved in blood sugar
regulation
– Reactive and fasting
4-31
Constancy of Blood
Glucose
• Glycemic response
– Glycemic index
• A measure of how fast
sugar is digested
https://www.diabetesnet.com/diabetes_food_
diet/glycemic_index.php
http://www.mendosa.com/gilists.htm
Glycemic Response
• The rate, magnitude, and duration of the rise in
blood glucose that occurs after a food or meal is
consumed.
– Glycemic index: a ranking of how a food affects blood
glucose compared to the response of a reference
food
– Glycemic load: an index of glycemic response
4-25
Accusations
Against Sugars
• Sugar causes
obesity
• Sugar causes
heart disease
Accusations
Against
Sugars
• Sugar causes misbehavior in children
and criminal behavior in adults
Accusations
Against
Sugars
• Sugar causes cravings and
addictions
– serotonin
Carbohydrate
Recommendations
• The RDA:
– Minimum amount required to provide
adequate glucose for the brain
– Set at 130 g/day (~ 420 kcalories)
• The Range of Healthy Intakes:
– Set at 45% to 65% of energy
– No more than 25% of energy should come
from added refined sugars
• An AI for Fiber:
– Set at 38g/day for young adult men and
25g/day for young adult women
4-37
Carbohydrate Content of Selections
from Each Food Group of MyPyramid
4-38
Calculating Percentage Energy
from Carbohydrate
4-39
Carbohydrates on Food Labels
• Grams of total carbohydrate, fiber, and
sugars listed
• Amounts of soluble and insoluble fiber not
required
• Total carbohydrate and fiber also listed as
a percent of the Daily Value
4-41
Looking for
Sugars and
Fibers on the
Food Labels
4-42
Looking for Sugars and Fibers on
the Food Labels
4-43
Translating Recommendations into
Healthy Diets
4-44
Alternatives to Sugar
• Artificial sweeteners vs.
sugar replacers (nutritive
sweeteners)
Alternative Sweeteners
• Acceptable Daily Intakes (ADIs) set by
FDA
• Cut down on kcalories in, but do not add
whole grains, fruits, and vegetables to the
diet
• Have been shown to reduce the incidence
of dental caries
• Usefulness for weight loss controversial
4-45
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Types of Alternative
Sweeteners
Saccharin
– 200–700 times sweeter than sugar
– No warning labels required since May 2000
• Aspartame
– Made of aspartic acid and phenylalanine
– Can be dangerous to people with
phenylketonuria (PKU)
• Sucralose (Trichlorogalactosucrose)
– Sold under the name “Splenda”
– Derived from sugar
4-46
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Types of Alternative
Acesulfame Sweeteners
K
– 200 times as sweet as sugar
– Heat stable
• Neotame
– Similar to aspartame, with stronger chemical
bond (cannot be broken down easily)
– 7000–13,000 times sweeter than sugar!
• Sugar alcohols
– Chemical derivatives of sugar
– Low-calorie: 0.2–3 kcalories/gram
– Can be described as “sugar free” on food
labels
4-47
Alternatives to Sugar
• Saccharine and cancer
• Aspartame and PKU
Metabolism
of
Aspartame
Sugar Alternatives on Food
Labels
High Fructose Corn Syrup
Unlike carbohydrates
made up of glucose,
fructose does not stimulate
the pancreas into
producing insulin.
Nor does it promote the
production of leptin, a
hormone made by fat cells.
Under normal conditions,
the amount of insulin and
leptin in the body signal to
the brain that you’ve had
enough to eat
Simple
Carbohydrates:
The Disaccharides
Sucrose
Sucrose = Glucose + Fructose
*Table sugar
*Found naturally in plants: sugar cane,
sugar beets, honey, maple syrup
*Sucrose may be purified from plant
sources into Brown, White and
Powdered Sugars.
It could be like paying with pennies
vs. paying with nickels.
The whole
thing could be
like a wooden
nickel or a
trick.
High
Fructose
Corn
Syrup
Simple Carbohydrates:
The Monosaccharides
1. Glucose C6H12O6
• The essential energy source
for all body functions.
•
•
•
Other names: Dextrose and
Blood Sugar.
A component of each
disaccharide.
The body’s main source of
energy.
Simple Carbohydrates:
The Monosaccharides
• Fructose:
• The sweetest of all sugars
– (1.5 X sweeter than sucrose)
• Occurs naturally in fruits and
honey
– “the fruit sugar”
Table 4.1 More and Less Refined Choices
• Recommendations:
– Choose more foods with less refined carbohydrates
– Choose fewer foods with refined carbohydrates and
added sugars
4-7
The Whole Grain Story
• A whole grain is the
entire kernel of grain
including:
– The bran: dietary
fiber and vitamins
– The germ: vitamin E,
protein, fibers,
riboflavin, thiamin,
and B6
– The endosperm:
starch, protein, some
vitamins and minerals
4-8
Choosing Whole Grains
4-9
Choosing Whole Grains
4-10
More on Carbohydrates and Health
• Diets high in sugars and refined
starches increase the demand for
insulin and may increase the risk for
developing diabetes.
• Diets high in whole grains and other
unrefined carbohydrates may reduce
the risk of heart disease.
• Diets high in indigestible carbohydrates
can relieve or prevent certain disorders
that are caused by pressure in the
lumen of the colon.
4-33