Transcript Carbohydrates

Chapter 4
The
Carbohydrates:
Sugar, Starch,
and Fiber
 2010 Cengage-Wadsworth
The Body’s Need for
Carbohydrates
• The primary role of carbohydrates is to
provide the body with energy (calories).
• Carbohydrates are the preferred fuel for the
brain and nervous system.
• Carbohydrates are the ideal fuel compared to
other alternatives:
 Less expensive than protein.
 High-fat diets are associated with chronic disease.
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Carbohydrate Basics
• Carbohydrates: compounds made of single
sugars or multiples of them and composed of
carbon, hydrogen, and oxygen atoms.
 carbo = carbon (C)
 hydrate = water (H2O)
• Complex carbohydrates: long chains of
sugars (glucose) arranged as starch or fiber.
Also called polysaccharides.
 poly = many
 saccharides = sugar unit
• Simple carbohydrates (sugars): the single
sugars (monosaccharides) and the pairs of
sugars (disaccharides) linked together.
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Carbohydrate Basics
• Carbohydrate-rich foods are
obtained almost exclusively from
plants.
Milk is the only animal-derived food
that contains significant
carbohydrate.
• All carbohydrates are composed of
single sugars, alone or in various
combinations.
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Simple Carbohydrates
• Single Sugars - Monosaccharides:
 Glucose: (GLOO-koce) the building block of
carbohydrate; a single sugar used in both plant and
animal tissues as quick energy. A single sugar is known
as a monosaccharide.
• mono = one
 Fructose: (FROOK-toce) fruit sugar—the sweetest of
the single sugars.
 Galactose: (ga-LACK-toce) another single sugar that
occurs bonded to glucose in the sugar of milk.
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Simple Carbohydrates
• Double Sugars - Disaccharides:
 Sucrose: (SOO-crose) a double sugar
composed of glucose and fructose. A double
sugar is known as a disaccharide.
• di = two
 Maltose: a double sugar composed of two
glucose units.
 Lactose: a double sugar composed of
glucose and galactose; commonly known as
milk sugar.
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Simple Carbohydrates
Added Sugars:
• Sugar cane and sugar
beets are purified to
make sucrose.
• Food examples include
white (table) sugar,
brown sugar, powdered
sugar.
• Sucrose is common in
sweets.
A sampling of foods
providing added sugars
to the diet.
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Simple Carbohydrates
• Enzymes: protein
catalysts. A catalyst
facilitates a chemical
reaction without itself
being altered in the
process.
 (Proteins are
discussed in Chapter
6.)
• Lactose intolerance:
inability to digest lactose
as a result of a lack of the
necessary enzyme lactase.
 Symptoms include nausea,
abdominal pain, diarrhea,
or excessive gas that
occurs anywhere from 15
minutes to a couple of
hours after consuming
milk or milk products.
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Complex Carbohydrates: Starch
Complex carbohydrates include starch
and fiber. All starchy foods are plant
foods.
•Starch: a plant polysaccharide composed of
hundreds of glucose molecules, digestible by
human beings.
•Polysaccharide: a long chain of 10 or more
glucose molecules linked together in straight or
branched chains; another term for complex
carbohydrates.
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Complex Carbohydrates: Starch
Sources of starch
include:
• Seeds such as
grains, peas and
beans.
• Legumes including
dried beans, lentils
and soybeans.
• Root vegetables
(yams) and tubers
(potatoes).
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Complex Carbohydrates: Starch
• Most societies have a staple grain that
provides most of the people’s food
energy.
• Staple grain: a grain used frequently
or daily in the diet. Examples include:




Corn in Mexico
Rice in Asia
Wheat in Canada, Europe and USA
Millet, rye, barley, and oats
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Complex Carbohydrates: Starch
• Refined: refers to the process by which the
coarse parts of food products are removed.
• Enriched: refers to a process by which the
B vitamins thiamin, riboflavin, niacin, folic
acid, and the mineral iron are added to refined
grains and grain products at levels specified
by law.
• Fortified foods: foods to which nutrients
have been added. Typically, commonly eaten
foods are chosen for fortification with added
nutrients to help prevent a deficiency of a
nutrient (iodized salt, milk with vitamin D) or
to reduce the risk of chronic disease (juices
with added calcium).
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Husk (chaff)
Endosperm
Bran
Bran
layers
Germ
A wheat
kernel
p. 110
Complex Carbohydrates: Fiber
• Fiber: the indigestible residues of food, composed
mostly of polysaccharides. The best known fibers are
cellulose, hemicellulose, pectin, and gums.
 Comes from the supporting structures of plants: leaves,
stems and seeds.
 Cannot be broken down by human digestive enzymes
although some may be broken down by bacteria residing
in the digestive tract.
 Fiber has few if any calories because it is not digested.
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Complex Carbohydrates: Fiber
• Insoluble fiber
includes the fiber
types called
cellulose,
hemicellulose, and
lignin.
• Insoluble fibers do
not dissolve in
water.
• Soluble fiber
includes the fiber
types called pectin,
gums, mucilages,
some hemicelluloses,
and algal substances
(for example,
carageenan).
• Soluble fibers either
dissolve or swell when
placed in water.
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Foods rich in insoluble fiber:
Bran
Rice
Foods rich in soluble fiber:
Barley
Legumes
Brown rice
Seeds
Broccoli
Oat bran
Green beans
Skins/peels
Carrots
Oats
Green peas
Wheat bran
Corn
Potatoes
Many veggies
Whole-grain
products
Fruits
Rye
Nuts
Insoluble fiber:
• Holds water in the
colon and increases
bulk to the stool.
• Stimulates muscles
and helps maintain
health and tone.
Soluble fiber:
• Binds cholesterol
compounds and may
lower blood
cholesterol.
• Improves body’s
handling of glucose.
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Diverticulosis: The outpocketings of intestinal linings that
balloon through the weakened intestinal wall muscles are known
as diverticula.
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Choosing Carbohydrates
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Choosing Carbohydrates
Added Sugars: Use Discretion
• Choose and prepare foods with little
added sugar (Dietary Guidelines).
Added Sugar: sugars and other caloric
sweeteners that are added to foods during
processing or preparation. Added sugars do
not include naturally occurring sugars that
are found in milk and fruit.
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Choosing Carbohydrates
• Choose most often the naturally
occurring sugars (DRI).
• For those who meet their nutrient
needs, maintain a “healthy body
weight” and still need additional
calories--maximum intake = 25%
or less for added sugars (DRI).
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Make Half Your Grains
Whole
• Breakfast: Try a higher-fiber grain: oatmeal,
whole-grain muffin, or whole-grain cereal
• Whole grains are low in fat and added sugars
• Baking recipes: Substitute whole-grain flour
for 1/4 of all-purpose flour
• Make a fiber-rich snack mix from whole grain
cereals, popcorn, and nuts
• Try whole-wheat pasta, rice, and breads
• Combine whole grains in mixed dishes
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How the Body Handles
Carbohydrates
• If the blood delivers more glucose than the
cells need, glycogen will be built.
 Glycogen (GLY-co-gen): a polysaccharide
composed of chains of glucose, manufactured in the
body and stored in liver and muscle.
• As a storage form of glucose, liver glycogen
can be broken down by the liver to maintain a
constant blood glucose level when
carbohydrate intake is inadequate.
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A. When a person overeats (feasting):
Food component:
Carbohydrate
is broken down in the body to:
Glucose
Glucose
and then stored as:
Liver and
muscle glycogen
stores
Body fat stores
B. When a person draws on stores (fasting):
Storage compound:
Liver and
muscle glycogen
stores
is broken down in the body to:
Glucose
Glucose
and then used for:
Energy
Fig. 4-4, p. 119
When a person eats, blood glucose
rises. High blood glucose stimulates
the pancreas to release insulin. Insulin
serves as a key for entrance of blood
glucose into cells. Liver and muscle
cells store the glucose as glycogen.
Excess glucose can also be stored as
fat.
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Later, when blood glucose is low, the
pancreas releases glucagon, which
serves as the key for the liver to break
down stored glycogen into glucose and
release it into the blood to raise blood
glucose levels.
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How the Body Handles
Carbohydrates
• Insulin: a hormone secreted by the
pancreas in response to high blood glucose
levels; it assists cells in drawing glucose from
the blood.
• Glucagon (glue-cuh-gon): a hormone
released by the pancreas that signals the liver
to release glucose into the bloodstream.
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Carbohydrates--Friend or Foe?
• Glycemic index (GI): a scale that ranks
carbohydrate-containing foods by how much they raise
blood glucose levels compared to a standard food such as
glucose or white bread. The glycemic load (GL) is a
measure of the extent to which blood glucose is raised by
a given amount of carbohydrate-containing food.
• Glycemic effect: the effect of food on a person’s
blood glucose and insulin response – how fast and high
the blood glucose rises and how quickly the body
responds by normalizing.
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High glycemic index
foods:
French, white, other
soft breads/bagels
Rice (medium-grain)
Certain cereals
(Cheerios, Corn
Flakes, Rice Krispies)
Waffles
Mashed potatoes
Honey, regular soft
drinks, jelly beans
Pretzels
Intermediate
glycemic index
foods:
Watermelon
Cream of Wheat,
instant oatmeal,
Shredded Wheat
Sourdough & rye
breads
Banana, pineapple,
orange juice
Low glycemic index
foods:
Whole-grain, heavy
breads
Rice (long-grain)
Bran cereals, toasted
Muesli cereal, whole
oats
Apples, oranges,
peaches
Ice cream
Baked beans, lentils,
other legumes
Popcorn
Carrots
Raisins
Milk, yogurt
Sweet potatoes
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Tomato soup
Hypoglycemia & Diabetes
• Hypoglycemia (HIGH-po-gligh-SEEM-eeuh): an
abnormally low blood glucose concentration—below 60
to 70 mg/100 mL.
• Ketosis: abnormal amounts of ketone bodies in the
blood and urine; ketone bodies are produced from the
incomplete breakdown of fat when glucose is
unavailable for the brain and nerve cells.
• Hyperglycemia: an abnormally high blood glucose
concentration, often a symptom of diabetes.
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Diabetes
• Diabetes (dye-uh-BEET-eez): a disorder
(technically termed diabetes mellitus)
characterized by insufficiency or relative
ineffectiveness of insulin, which renders a
person unable to regulate the blood glucose
level normally.
 Type 1 diabetes
 Type 2 diabetes
 Gestational diabetes (see Chapter 11)
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Sugar and Health
• Research studies have not shown a direct link
between sugar and obesity, diabetes, heart
disease, hyperactivity in children or criminal
behavior.
• Empty-calorie foods: a phrase used to
indicate that a food supplies calories but
negligible nutrients.
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 2010 Cengage-Wadsworth