_ fructose -glucose_ _glucose-glucose_ by wuzhenguang


									                Chapter 4
Carbohydrates: Sugar, Starch,
    Glycogen, and Fiber
   Nutrition: Concepts & Controversies, 12e
           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
 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.

 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



                Water                    Fig. 4.1, p. 108
     A Close Look at Carbohydrates -
 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

Three types of

…join together to
make three types of

                         Sucrose                  Maltose                   Lactoseb
                 (fructose-glucose)           (glucose-glucose)            (glucose-

aGalactose   does not occur in foods singly but only as part of lactose.
bThe 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.”


For convenience, glucose is symbolized as

                                                           Fig. 4.2, p. 109
     A Close Look at Carbohydrates –
 Polysaccharides
   Starch
      Plant’s storage form of glucose
   Glycogen
   Fiber
 Nutrition
   For a plant
   For a human
How Glucose Molecules Join to
   Form Polysaccharides

Starch (unbranched) Starch (branched)          Glycogen                       Cellulose
Starch Glucose units are linked         Glycogen Glycogen          Cellulose (fiber) The
in long, occasionally branched          resembles starch in        bonds that link glucose
chains to make starch. Human            that the bonds between     units together in
digestive enzymes can digest            its glucose units can be   cellulose are different
these bonds, retrieving glucose.        broken by human            from the bonds in starch
Real glucose units are so tiny that     enzymes, but the           or glycogen. Human
you can’t see them, even with the       chains of glycogen are     enzymes cannot digest
highest-power light microscope.         more highly branched.      them.             Fig. 4.3, p. 110
     A Close Look at Carbohydrates –
 Storage form of glucose
   Animal bodies
 Chains are longer than starch
   More highly branched
 Undetectable in meats
     A Close Look at Carbohydrates -
 Human digestive
  enzymes cannot
  break bonds
   Bacteria in large
      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
        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
       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
                                      stores bile
     Liver uses blood
      cholesterol to
        make bile                     3.
                                            Intestine: bile
                                           aids digestion;
                                            binds to fiber
          A little cholesterol
          in bile reabsorbed
            into the blood

                                     Fiber and bile
                                      excreted in

A. High-fiber diet

                                                              Fig. 4.6a, p. 116
                                    stores bile
     1.                        2.

     Liver uses blood
      cholesterol to                  3.
        make bile
                                        Intestine: bile
                                        aids digestion
            Much of the
          cholesterol in bile
          absorbed into the
                                     Little bile

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,


                      Fig. 4.7, p. 117

      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
 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 Whole-
               Grain 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
       beard                      (chaff)

Stem               A kernel of

                 A wheat plant


                                            Fig. 4.8, p. 120
      Refined, Enriched, and Whole-
               Grain 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
                                                      Small intestine

Fiber, starch,                                                  wall cells Capillary
monosaccharides,                                                                           An enzyme from the
and disaccharides                                                                          pancreas digests most
enter the stomach     1                                                                2
                                         1                               3
                                                                                           of the starch to
and pass into the                                                                          disaccharides.
small intestine.                                                                           Enzymes on the surface
Some of the starch                                                                         of cells that line the
is partially broken                                         2                4         3   intestine split
down by an enzyme                                                                          disaccharides to
from the salivary                                                                          monosaccharides.
glands before it
reaches the small                                                                          Monosaccharides enter
intestine.                                                                             4   capillaries, and are then
                                                                                           delivered to the liver via
                                                                                           the portal vein.
Fiber and resistant                                                                        The liver can convert
starch travel         6                                                                5   galactose and fructose
unchanged to the                             6
                                                                                           to glucose.

          galactose               Key:
           sucrose                                  fiber
           maltose                                  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
 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

               (6-carbon compound)


           Carbon             2-carbon
           dioxide            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
      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
 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   Glucose

      87   Mashed potato, instant; rice crackers
           Rice milk
           Baked potato, boiled potato
           Oatmeal, instant
           Sports drinks, jelly beans
           Watermelon, doughnut
      75   Pumpkin, popcorn, bagel
           White bread, wheat bread, white rice
      62   Raisins, brown rice
           Couscous, sucrose (table sugar)
           Cola, pineapple
           Ice cream
           Oatmeal, cooked
           Corn, pound cake
           Bananas, mangoes
      50   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
      37   Tomato juice, navy beans, apples, pears
           Yogurt, milk
           Soy milk
           Butter beans, lentils
           Chickpeas (garbanzo beans)
           Kidney beans
      25   Barley
           Cashews, cherries

LOW                                                          Fig. 4.13, p. 129
 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
       <4%                  8%–9.9%
       4%–5.9%              ≥10%

 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
              <4%          8%–9.9%
Key:          4%–5.9%      ≥10%
       <4% 6%–7.9%            8%–9.9%
       4%–5.9%                ≥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

                          • Enlarged fat mass
• Reduced glucose
                          • Elevated blood
  use for fuel              lipids
• Increased fat stores
                          • Inflammation

                         • Insulin resistance
• Type 2 diabetes
• Hormone
                                                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
   Type 2 diabetes
    vs. type 1 diabetes

 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
        Controversy 4
     Accusation 1: Carbohydrates Are
              Making Us Fat
 Americans are
   Greater
    consumption of
      300-500 per day
 Epidemiological
 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
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
   Fructose causes
    fats to accumulate
    in blood and liver
   Metabolic activities
    of concern
     Accusation 5: Blood Insulin Is To
 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

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