Transcript CARBOHYDRATES

CARBOHYDRATES
Chapter 5
Carbohydrates
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Made of carbon, hydrogen, and oxygen in
a 1:2:1 ratio
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Primary fuel source for body cells
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Divided into two main classes:
Simple sugars
 Complex sugars
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MONOSACCHARIDES
GLUCOSE
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Also called hexose or
dextrose
Principle building
block of all other
carbohydrates
Typically exists in the
ring form
FRUCTOSE
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Also called levulose
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Isomer of glucose
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Metabolized into glucose by the
liver
Small amounts are converted into
glycogen, lactic acid, or fat
Found in fruit, honey, and high
fructose corn syrup
GALACTOSE
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Not usually found free in nature in
large quantities
Isomer of glucose
Typically found as a subunit of
lactose
Converted to glucose by the liver
Used as an immediate energy
source or is stored as glycogen
Other Monosaccharides
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Ribose
Five carbon sugar
 Used in the formation of RNA
 Very little present in our diet
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Deoxyribose
Five carbon sugar
 Used in the formation of DNA
 Not considered a nutrient of our diet since our
bodies can make all that it ever needs.
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DISACCHARIDES
MALTOSE
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Constructed by a condensation reaction
Composed of two glucose molecules
Possesses an alpha bond
Commonly produced by fermentation reactions called
malting
Most maltose digested is the result of starch digestion
SUCROSE
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Constructed by a condensation reaction
Composed of one glucose and one fructose
Possesses an alpha bond
Commonly called table sugar and is found in plants such
as sugar cane and maple syrup
Purified to form brown, white, and powdered sugars
LACTOSE
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Constructed by a condensation reaction
Composed of one glucose and one galactose
Possesses a beta bond
Beta bonds are difficult to digest
Primary sugar in milk and milk products
OLIGOSACCHARIDES
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3-10 monosaccharides: raffinose
and stachyose
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Found in beans and legumes
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Not digested by the body
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Metabolized by bacteria in the
large intestine
Raffinose=galactose+glucose+fruc
tose
Stachyose=galactose+galactose+
glucose+fructose
POLYSACCHARIDES
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Digestible polysaccharides:
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Starch
Amylose
 Amylopectin
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Glycogen
Non-digestible polysaccharides: fibers
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Soluble fiber
Insoluble fiber
STARCHES
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3000 monosaccharides
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Contain alpha bonds
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Amylose is straight chain
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Amylopectin is branched
chain
High Glycemic Index
GLYCOGEN
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Storage form of glucose
in animals and humans
Structure is similar to
amylopectin but with
more complex branching
Numerous alpha bonds
Found in liver (400 kcal)
and muscles (1400 kcal)
Fiber
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Dietary fiber= fibers found naturally in
foods
Functional fibers= fiber added to foods
that has shown to provide health benefits
Total fiber= dietary fiber + functional fiber
Chemical Composition of Fibers
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Contain beta bonds
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Insoluble: not fermented
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Cellulose
Hemicellulose
Lignin*
Soluble: 1.5-2.5 kcal/g
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Gum
Pectin
Mucilage
Fibers
Carbohydrate Digestion
Within the Mouth
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Saliva contains amylase
Converts
polysaccharides, starch,
into oligosaccharides,
maltose, and glucose
Broken down by
hydrolysis reaction
Within the Stomach
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The acidic environment
of the stomach inhibits
the action of salivary
amylase
Within the Small Intestines
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Pancreatic amylase
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Converts
oligosaccharides to
disaccharides
Intestinal cells release
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Maltase
Lactase
Sucrase
CARBOHYDRATE ABSORPTION
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Monosaccharide
absorption occurs in
the duodenum
Glucose and galactose
by active absorption
Fructose by facilitated
diffusion
CARBOHYDRATE ABSORPTION
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Portal vein transports absorbed
monosaccharides to the liver
Liver can then:
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Transform them to glucose
Release them back to the blood stream
Store it as glycogen
FUNCTIONS OF
CARBOHYDRATES
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Supplies energy
Protein sparing
Prevents ketosis
Food sweeteners
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Fructose
Sucrose
Glucose
Maltose
Galactose
FUNCTIONS OF DIETARY FIBER
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Promotes regularity and
softer, larger stool
Reduces hemorrhoids and
diverticula
DIVERTICULOSIS
FUNCTIONS OF DIETARY FIBER
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Promotes regularity and softer,
larger stool
Reduces hemorrhoids and
diverticula
Aids weight control
Causes a filling of fullness
Slows glucose absorption
Decrease in colon cancer
Reduces cholesterol absorption
Reduces heart disease
RECOMMENDED
CARBOHYDRATE INTAKE
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RDA is 130 g/day for adults
50-100 g of CHO/day to prevent ketosis
Recommended: 45-65% of total kcal
180-330 g of CHO/day (primarily from
white bread, soda, baked goods)
50% of total kcal
Worldwide the CHO intake is +70%
RECOMMENDED FIBER INTAKE
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Adequate Intake is 25 g/day for women and 38
g/day for men (14g/1000kacl)
Daily Value= 25g/day for 2000 kcal diet
Average U.S. intake= 13-17 g/day
Sample Menus
Sample Menus
PROBLEMS WITH
HIGH SUGAR INTAKES
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Empty calories
Dental caries
Glycemic index=the blood glucose response to a
given food compared to a standard
Glycemic load=the amount of Carbohydrate in
food times the glycemic index for that food.
Related to structure, fiber content, amount of
processing, and macronutrient content
Effects of Ingesting
High Glycemic Load Foods
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Stimulates insulin release
Insulin increases blood triglyceride levels
 Insulin increases LDL
 Insulin increase fat synthesis
 Increased risk for CVD
 Muscles may become resistant to insulin
 Increases risk of developing diabetes
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Become hungry quicker
PROBLEMS WITH HIGH
INTAKES OF DIETARY FIBER
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Too much fiber (>60 g/day) will:
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Require extra intake of fluids
Bind to some vitamins
Develop phytobezoars
Fill the stomach of a young child quickly
Lactose Maldigestion
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Primary lactose maldigestion
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75% of world population
Begins to develop around age 3 to 5 years
Secondary lactose maldigestion
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Temporary decrease in lactase production
25% of North American population
Increases with age
FOOD SWEETENERS
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Nutritive sweeteners
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Sugars
Sugar alcohols
Alternative sweeteners
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Saccharin
Aspartame
Neotame
Acesulfame-K
Sucralose
Read the Nutrition
Perspective
Pp 171-176