Transcript fiber

Chapter 4
Carbohydrates: Sugar, Starch,
Glycogen, and Fiber
Nutrition: Concepts & Controversies, 12e
Sizer/Whitney
Learning Objectives
 Describe the major types of carbohydrates,
and identify their food sources.
 Describe the various roles of carbohydrates
in the body, and explain why avoiding
dietary carbohydrates may be ill-advised.
 Summarize how fiber differs from other
carbohydrates and how fiber may contribute
to health.
Learning Objectives
 Explain how complex carbohydrates are
broken down in the digestive tract and
absorbed into the body.
 Describe how hormones control blood
glucose concentrations during fasting and
feasting.
 Explain the term glycemic index and how it
may relate to diet planning.
Learning Objectives
 Describe the scope of the U.S. diabetes
problem and educate someone about the
long- and short-term effects of untreated
diabetes and prediabetes.
 Name components of a lifestyle plan to
effectively control blood glucose and
describe the characteristics of a diet that
can assist in managing type 2 diabetes.
Learning Objectives
 Compare the symptoms of postprandial
hypoglycemia with those of fasting
hypoglycemia, and name some diseases
associated with the latter type.
 Discuss current research regarding the
relationships among dietary carbohydrates,
obesity, diabetes, and other ills.
Carbohydrates
 Ideal nutrients
 Energy needs
 Feed brain and nervous system
 Keep digestive system fit
 Keep your body lean
 Digestible and indigestible carbohydrates
 Complex vs. simple carbohydrates
A Close Look at Carbohydrates
 Contain the sun’s radiant energy
 Green plants
 Photosynthesis
 Glucose
 Plants do not use all of the energy stored in
their sugars
 Carbohydrate-rich foods
 Plants
 Milk
Carbohydrate – Mainly Glucose –
Is Made by Photosynthesis
Carbon dioxide
Sun
Oxygen
Chlorophyll
Glucose
Water
Fig. 4.1, p. 108
A Close Look at Carbohydrates Sugars
 Six sugar molecules
 Monosaccharides
 Glucose, fructose, galactose
 Disaccharides
 Lactose, maltose, and sucrose
 Digestion of mono- and disaccharides
 Chemical names end in -ose
How Monosaccharides Join to
Form Disaccharides
Fructose
Glucose
Galactosea
Maltose
Lactoseb
Three types of
monosaccharides…
…join together to
make three types of
disaccharides.
Sucrose
(fructose-glucose)
aGalactose
bThe
(glucose-glucose)
(glucosegalactose)
does not occur in foods singly but only as part of lactose.
chemical bond that joins the monosaccharides of lactose differs from
those of other sugars and makes lactose hard for some people to digest—
lactose intolerance (see later section).
Fig. 4.2, p. 109
A note on the glucose symbol:
The glucose molecule is really a ring of 5
Carbons and 1 oxygen plus a carbon “flag.”
Carbons
Oxygen
For convenience, glucose is symbolized as
or
Fig. 4.2, p. 109
A Close Look at Carbohydrates –
Starch
 Polysaccharides
 Starch
 Plant’s storage form of glucose
 Glycogen
 Fiber
 Nutrition
 For a plant
 For a human
How Glucose Molecules Join to
Form Polysaccharides
Glucose
Starch (unbranched) Starch (branched)
Starch Glucose units are linked
in long, occasionally branched
chains to make starch. Human
digestive enzymes can digest
these bonds, retrieving glucose.
Real glucose units are so tiny that
you can’t see them, even with the
highest-power light microscope.
Glycogen
Cellulose
Glycogen Glycogen
resembles starch in
that the bonds between
its glucose units can be
broken by human
enzymes, but the
chains of glycogen are
more highly branched.
Cellulose (fiber) The
bonds that link glucose
units together in
cellulose are different
from the bonds in starch
or glycogen. Human
enzymes cannot digest
them.
Fig. 4.3, p. 110
A Close Look at Carbohydrates –
Glycogen
 Storage form of glucose
 Animal bodies
 Chains are longer than starch
 More highly branched
 Undetectable in meats
A Close Look at Carbohydrates Fibers
 Human digestive
enzymes cannot
break bonds
 Bacteria in large
intestine
 Fermentation
 Soluble vs.
insoluble fibers
The Need for Carbohydrates
 Critical energy source
 Nerve cells and brain
 Preferred dietary sources
 Starchy whole foods
 Complex carbohydrates
 Vital roles in the functioning body
The Need for Carbohydrates
 Weight loss
 Caloric contribution
 Conversion into fat storage
 Refined sugars
 Increase fiber-rich whole foods
 Reduce refined white flour and added
sugars
Why Do Nutrition Experts
Recommend Fiber-Rich Foods?
 Health benefits
 Reduced risk of heart disease
 Reduced risk of hypertension
 Reduced risk of diabetes
 Reduced risk of bowel disease
 Promotion of healthy body weight
 Sources of fiber
Characteristics, Sources, and
Health Effects of Fibers
Fiber Composition of Common
Foods
Why Do Nutrition Experts
Recommend Fiber-Rich Foods?
 Lower cholesterol and heart disease risk
 Complex carbohydrates
 More than just fiber
 Viscous fiber
 Cholesterol synthesis
 Blood glucose control
 Whole grains
 Soluble fibers
One Way Fiber in Food May
Lower Cholesterol in the Blood
2.
1.
Liver uses blood
cholesterol to
make bile
Gallbladder
stores bile
3.
Intestine: bile
aids digestion;
binds to fiber
5.
A little cholesterol
in bile reabsorbed
into the blood
4.
Fiber and bile
excreted in
feces
A. High-fiber diet
Fig. 4.6a, p. 116
Gallbladder
stores bile
2.
1.
Liver uses blood
cholesterol to
make bile
3.
Intestine: bile
aids digestion
5.
Much of the
cholesterol in bile
absorbed into the
blood
4.
Little bile
excreted
B. Low-fiber diet
Fig. 4.6b, p. 116
Why Do Nutrition Experts
Recommend Fiber-Rich Foods?
 Maintenance of digestive tract health
 All kinds of fiber
 Ample fluid intake
 Benefits of fiber
 Constipation, hemorrhoids, appendicitis,
diverticulosis
Diverticula
Diverticula
Colon
Fig. 4.7, p. 117
Diverticulum
Fig. 4.7, p. 117
Why Do Nutrition Experts
Recommend Fiber-Rich Foods?
 Digestive tract cancer and inflammation
 Ways fiber works against cancer
 Dilution
 Folate
 Resident bacteria
 Butyrate
 Recommended dietary sources
 Healthy weight management
 Appetite control
Fiber Recommendations and
Intakes
 Few people in U.S. meet recommendations
 20-35 grams of fiber daily
 Based on energy needs, age, and gender
 Adding fiber to diet
 Too much fiber?
 Dangers of excess
 Binders in fiber
 Chelating agents
 Cause of deficiencies
Usefulness of Carbohydrates
Refined, Enriched, and WholeGrain Foods
 Bread supplies much carbohydrate for
many people
 Kernel (whole grain) has four main parts
 Germ
 Endosperm
 Bran
 Husk
A Wheat Plant and a Single
Kernel of Wheat
Head
husk
(chaff)
beard
kernels
bran
(14%)
endosperm
(83%)
germ
(2.5%)
Stem
A kernel of
wheat
A wheat plant
Root
Fig. 4.8, p. 120
Refined, Enriched, and WholeGrain Foods
 U.S. Enrichment
Act of 1942
 Required additives
 Addition in 1996
 Advantages of
whole grains vs.
enriched grains
 Finding the whole
grains in foods
Nutrients in Whole-Grain, Enriched
White, and Unenriched White Breads
Bread Labels Compared
From Carbohydrates to Glucose –
Digestion & Absorption
 Starch and disaccharides are broken down
 Monosaccharides for absorption
 Starch
 Begins in the mouth
 Splits starch into maltose
 Digestion ceases in the stomach
 Digestion resumes in small intestine
 Pancreas
 Resistant starch
From Carbohydrates to Glucose –
Digestion & Absorption
 Sugars
 Split to yield free monosaccharides
 Enzymes on small intestine lining
 Travel to the liver
 Fiber
 Fermented by bacteria in the colon
 Odorous gas
 Gradually increase fiber intakes
How Carbohydrate in Food
Becomes Glucose in the Body
Esophagus
Pancreas
Liver
Stomach
Small intestine
Large
intestine
(colon)
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.
Fiber and resistant
starch travel
unchanged to the
colon.
Intestinal
wall cells Capillary
1
2
1
3
2
4
3
4
6
5
6
An enzyme from the
pancreas digests most
of the starch to
disaccharides.
Enzymes on the surface
of cells that line the
intestine split
disaccharides to
monosaccharides.
Monosaccharides enter
capillaries, and are then
delivered to the liver via
the portal vein.
The liver can convert
galactose and fructose
to glucose.
5
galactose
lactose
sucrose
maltose
Key:
fiber
starch
Fig. 4.11, p. 124
Why Do Some People Have
Trouble Digesting Milk?
 Ability to digest milk carbohydrates varies
 Lactase
 Made by small intestine
 Symptoms of intolerance
 Nausea, pain, diarrhea, and gas
 Milk allergy
 Nutritional consequences
 Milk tolerance and strategies
The Body’s Use of Glucose
 Basic carbohydrate unit used for energy
 Body handles glucose judiciously
 Maintains an internal supply
 Tightly controlling blood glucose
concentrations
 Brain, nervous system, red blood cells
Splitting Glucose for Energy
 Glucose is broken
in half
 Can reassemble
 Broken into
smaller molecules
 Irreversible
 Two pathways
Carbon atoms
Bonds
Glucose
(6-carbon compound)
3-carbon
compound
Carbon
dioxide
2-carbon
compound
2 molecules of
carbon dioxide
Fig. 4.12, p. 126
Splitting Glucose for Energy
 Glucose can be converted to fat
 Fat cannot be converted to glucose
 Dependence on protein when insufficient
carbohydrate
 Protein-sparing action
 Ketosis
 Shift in body’s metabolism
 Disruption of acid-base balance
 DRI minimum of digestible carbohydrate
How Is Glucose Regulated in the
Body?
 Two safeguard activities
 Siphoning off excess blood glucose
 Replenishing diminished glucose
 Two hormones
 Insulin
 Signals body tissues to take up glucose
 Glucagon
 Triggers breakdown of glycogen
 Epinephrine
Handling Excess Glucose
 Body tissue shift
 Burn more glucose
 Fat is left to circulate and be stored
 Carbohydrate storage as fat
 Liver breakdown and assembly
 Costs a lot of energy
 Weight maintenance
 Dietary importance and composition
Glycemic Index of Food
 Elevation of blood glucose and insulin
 Food score compared to standard food
 Diabetes
 Glycemic load (GL)
 Lower GL = less glucose guild up and less
insulin needed
 Limitations of glycemic index
 Resist notion of “good” or “bad” foods
Glycemic Index of Selected Foods
HIGH 100
87
75
62
50
37
25
Glucose
Mashed potato, instant; rice crackers
Rice milk
Cornflakes
Baked potato, boiled potato
Oatmeal, instant
Sports drinks, jelly beans
Watermelon, doughnut
Pumpkin, popcorn, bagel
White bread, wheat bread, white rice
Raisins, brown rice
Couscous, sucrose (table sugar)
Honey
Cola, pineapple
Ice cream
Oatmeal, cooked
Corn, pound cake
Bananas, mangoes
Rye bread, orange juice
Green peas, baked beans, pasta
Grapes, corn tortillas
Chocolate pudding, chocolate candy
Bran cereals, black-eyed peas, peaches, oranges
Apple juice, dates, carrots
Tomato juice, navy beans, apples, pears
Yogurt, milk
Soy milk
Butter beans, lentils
Chickpeas (garbanzo beans)
Kidney beans
Barley
Cashews, cherries
Soybeans
12
LOW
Peanuts
Fructose
0
Fig. 4.13, p. 129
Diabetes
 Prevalence of diabetes
 Adults
 Children
 Prediabetes
 Importance of testing
 Perils of diabetes
 Toxic effects of excess glucose
 Inflammation
 Circulation problems
Prevalence of Diabetes Among
Adults in the United States
Key:
<4%
4%–5.9%
8%–9.9%
≥10%
6%–7.9%
1997: Ten states had a prevalence of
diabetes of less than 4% and only five
states had a prevalence of 6% or greater.
Fig. 4.14, p. 130
Key:
<4%
4%–5.9%
<4% 6%–7.9%
4%–5.9%
6%–7.9%
8%–9.9%
≥10%
8%–9.9%
≥10%
2007: No state had a prevalence of diabetes of
less than 4%; all but three states had a
prevalence of 6% or greater, with eight states
reporting a prevalence of 10% or greater.
Fig. 4.14, p. 130
Warning Signs of Diabetes
Type 1 Diabetes
 5 to 10 percent of cases
 Common age of occurrence
 Autoimmune disorder
 Own immune system attacks pancreas
 Lose ability to produce insulin
 External sources of insulin
 Fast-acting and long-acting forms
Type 2 Diabetes




Predominant type of diabetes
Lose sensitivity to insulin
Obesity underlies many cases
Other factors foreshadowing development
 Middle age and physical inactivity
 Body fat accumulation
 Genetic inheritance
 Prevention
Type 1 and 2 Diabetes Compared
An Obesity-Diabetes Cycle
• Genetic inheritance
• Excess food energy
• Inadequate physical activity
• Obesity
• Reduced glucose
use for fuel
• Increased fat stores
• Type 2 diabetes
• Hormone
imbalance
• Enlarged fat mass
• Elevated blood
lipids
• Inflammation
• Insulin resistance
Fig. 4.15, p. 132
Management of Diabetes
 Controlling blood glucose is key
 Monitoring blood glucose levels
 Taking medications
 Control body fatness
 Establish good eating patterns
Management of Diabetes
 Nutrition
 Goal: blood glucose levels in normal range
 Control carbohydrate intake
 Amount rather than source seems to matter
 Carbohydrate recommendations
 Varies with glucose tolerance
 Exchange system
Management of Diabetes
 Nutrition
 Carbohydrate timing
 Evenly spaced
 Sugar alcohols
 Advantages
 Artificial sweeteners
 Weight control
Management of Diabetes
 Physical activity
 Benefits of regular
activity
 Type 2 diabetes
vs. type 1 diabetes
Hypoglycemia
 Rare, but true disease
 Abnormally low blood glucose
 Postprandial hypoglycemia
 Requires test to detect
 Fasting hypoglycemia
 Symptoms
 Methods to reduce symptoms
Finding Carbohydrates in Foods
 Fruits
 Vary in water, fiber, & sugar concentrations
 Juice
 Vegetables
 Breads, grains, cereals, rice, & pasta
 Brown color does not equal whole grain
 Low-fat and low-sugar choices
Finding Carbohydrates in Foods
 Meat, poultry, fish, dry beans, eggs, & nuts
 Nuts and legumes
 Milk, cheese, & yogurt
 High-quality protein
 Oils, solid fats, & added sugars
 Naturally occurring vs. added sugars
 Honey
Finding Carbohydrates in Foods
 The nature of sugar
 Teaspoon values
 High-fructose corn syrup
 Concentrated juice sweeteners
 Ways to magnify sweetness without calories
Are Carbohydrates “Bad” for
Health
Controversy 4
Accusation 1: Carbohydrates Are
Making Us Fat
 Americans are
fatter
 Greater
consumption of
calories
 300-500 per day
 Epidemiological
studies
 Weight loss
Percentage of Calories from Energy
Nutrients, U.S., 1977-2006
Daily Energy Intake Over Time
Accusation 2: Carbohydrates
Cause Diabetes
 Obesity and diabetes
 Refined carbohydrates and diabetes
 Native Americans
 Glycemic load and diabetes
 Whole foods
Accusation 3: Added Sugars
Cause Obesity and Illness
 Current trends
 Daily
 Per year
 Relationship with
disease
Added Sugars: Average U.S. Supply per
Person Compared with USDA Prudent
Upper Intake Limits
Accusation 4: High-Fructose Corn
Syrup Harms Health
 Villainy has been exaggerated
 Nature of HFCS
 Half of added sugar in U.S. food supply
 Obesity
 HCFS not a proven cause
 Liquid sugar and calorie control
 Appetite regulation
 Fructose does not stimulate insulin release
Accusation 4: High-Fructose Corn
Syrup Harms Health
 Effects on lipid
metabolism
 Fructose causes
fats to accumulate
in blood and liver
 Metabolic activities
of concern
Accusation 5: Blood Insulin Is To
Blame
 Presence of insulin
 Body tends to store energy
 Claims made about insulin
 Expert standing on insulin
 Insulin does not cause accumulation of
excess body fat