Download The Carbohydrates: Sugars, Starch, & Fibers

The Carbohydrates:
Sugars, Starch, & Fibers
H
H-C-O-H
C
H H
C
H-O O-H
C
H
O
H
H
C
O-H
C The Structure of Glucose
O-H
Carbohydrates
 Compounds composed of carbon, oxygen, and
hydrogen arranged as monosaccharides or
multiples of monosaccharides. Most, but not all,
have a ratio of one carbon molecule to one
water molecule: CH2O.
 Carbo = carbon (C)
 Hydrate = with water (H2O)
Simple Versus Complex
 Simple- monosaccharides and disaccharides,
the sugars.
 Complex- polysaccharides composed of straight
or branched chain monosaccharides, starches
and fibers.
 Mono = one
 Di = two
 Poly = many
Simple CarbohydratesMonosaccharides
All have the same numbers and kinds of
atoms, but in different arrangements which
accounts for their differing sweetness.
Glucose, also known as dextrose.
Fructose, the sweetest of the
monosaccharides, found abundantly in
fruits and honey.
Galactose
Simple CarbohydrateDisaccharides
The disaccharides are pairs of the
monosaccharides. Glucose appears in all
three.
Maltose = glucose + glucose
Sucrose = glucose + fructose, table sugar.
Lactose = glucose + galactose, milk sugar.
Complex Carbohydrates
Glycogen
Starches
Fibers
Glycogen
Glycogen- an animal polysaccharide
composed of glucose. It is manufactured
and stored in the liver and muscles as a
storage form of glucose. Its branched
chain structure of glucose molecules
allows for rapid hydrolysis into glucose for
energy.
Starches
Starches- plant polysaccharides
composed of glucose.
Fibers
Fibers- in plant foods, the nonstarch
polysaccharides that are not digested by
human digestive enzymes, although some
are digested by GI tract bacteria. Fibers
include cellulose, hemicelluloses, pectins,
gums, and mucilages as well as the
nonpolysaccharides lignins, cutins, and
tannins.
Soluble Fiber
Major Food Source
 Fruits (apples, citrus)
 oats
 barley
 legumes
Action In Body
 Delays GI transit
 Delays glucose
absorption
 Lowers cholesterol
Insoluble Fiber
Major Food Source
 Wheat bran
 Corn bran
 Whole grain breads
 Cereals
 Vegetables
Action In Body
 Accelerate GI transit
 Increase fecal weight
 Promotes BM
Classifications of Fibers
 Cellulose- the primary constituent of plant cell
walls. Composed of glucose molecules
connected in long unbranched chains. The
bonds are resistant to digestion of human
enzymes.
 Hemicelluloses- the main constituent of cereal
fibers. They are composed of monosaccharide
backbones with branching side chains. Some
are soluble while others are not.
Classifications Of Fibers
{continued}
 Pectins- consist of a backbone derived from
carbohydrate with side chains of various
monosaccharides. These are found in fruits and
vegetables. Commonly used by the food
industry to thicken jellies or to keep salad
dressings from separating.
 Gums and Mucilages- composed of various
monosaccarides and their derivatives.
Commonly used by the food industry as
stabilizers.
Classifications Of Fibers
{Continued}
Lignin- is a nonpolysaccharide fiber with a
three dimensional structure. This structure
provides strength and rigidity. Few foods
people eat contain lignin. It is found in the
woody parts of vegetables and the small
seeds of fruits like strawberries.
Classifications Of Fibers
{Continued}
Other classifications of fibersWater-holding capacity
Viscosity
Cation-exchange capacity
Bile-binding capacity
Fermentability
Digestion And Absorption
Of Carbohydrates
 In the mouth- chewing stimulates the flow of
saliva. Salivary amylase starts to work by
hydrolyzing the long chains into shorter ones.
 In the stomach- there are no enzymes produced
by the stomach which digest starch. Fiber delays
gastric emptying.
 In the small intestines- most of the work is done
here. Pancreatic amylase enters the intestine
via the pancreatic duct. Specific enzymes
dismantle each of the dissacharides.
Digestion And Absorption Of
Carbohydrates {Continued}
 In the large intestines- insoluble fiber attracts
water which softens the stool for passage.
Bacteria also ferment fiber which generates gas.
 Absorption into the bloodstream- monosaccharides, the end products of carbohydrate
digestion, enter the capillaries of the intestinal
villi. From there they travel to the liver via the
portal vein.
Glucose In The Body
 The primary role of carbohydrates in the body
is to supply the body’s cells with glucose for
energy.
 Storing glucose as glycogen
 Making glucose from protein
 Making ketone bodies from fat fragments
 Converting glucose to fat
Regulating Blood Glucose
Glucose homeostasis- the body must maintain blood
glucose within normal limits to nourish the cells.
The regulating hormonesInsulin- secreted by special cells of the pancreas in
response to increased blood glucose
concentrations to control the transport of glucose
from the blood to the cells.
Glucagon- secreted by special cells of the pancreas
in response to low blood glucose concentrations, it
elicits the release of glucose from storage.
Regulating Blood Glucose
{Continued}
Epinephrine (adrenaline)- “fight-or-flight”.
When a person experiences stress, this
hormone acts quickly, ensuring that the body
cells will have fuel in emergency situations by
mobilizing glucose from the liver.
Falling Outside The Normal
Range
 Diabetes- a disorder of carbohydrate metabolism
resulting from inadequate or ineffective insulin.
 Hypoglycemia- an abnormally low blood glucose
concentration.
 High blood sugar may result in confusion and difficulty
breathing, if left untreated could be fatal.
 Low blood sugar could result in dizziness and
weakness, if left untreated could be fatal.
Health Effects Of Sugar
Estimated that on the average each
person consumes ~45 pounds of sugar
per year.
Can contribute to nutrient deficiencies by
supplying energy without supplying
nutrients. “Empty calories”
Can contribute to tooth decay.
Recommended Intakes Of
Sugars
Dietary guidelines for Americans urge only
moderate consumption of sugars.
Recommendations specify that sugar
should only account for 10% or less of the
day’s total energy intake.
Health Effects Of Starches
And Fibers
 Foods rich in complex carbohydrates tend to be
low in fat.
 Foods rich in soluble fibers lower blood cholesterol,
reducing the risk of heart disease.
 Diets high in fruits and vegetables, especially citrus
fruits and green and yellow vegetables, help
prevent certain types of cancers from forming.
 Dietary fibers enhance intestinal health.
Recommended Intakes Of
Starches And Fibers
Dietary recommendations suggest that
carbohydrates provide 55-60% of energy
requirements.
The American Dietetic Association
suggests 20-35 grams of fiber daily.