Chapter
4
Carbohydrates
Carbohydrates
• Carbohydrates are organic compounds
that contain carbon (C), hydrogen (H),
and Oxygen (O) in the ratio of 1 carbon
atom and 1 oxygen atom for every 2
hydrogen atoms.
• The sugar glucose contains 6 carbon
atoms, 12 hydrogen atoms, and 6
oxygen atoms.
• C6H12O6
Carbohydrates
• Two or more sugar molecules can be
assembled to form increasingly
complex carbohydrates.
• The two main carbohydrates found in
food are simple carbohydrates (sugars)
and complex carbohydrates (starches
and dietary fiber).
Simple Sugars: Monosaccharides and
Disaccharides
• Simple carbohydrates are naturally
present as simple sugars in fruits, milk,
and other foods.
• Plant carbohydrates can be refined to
produce sugar products like table sugar
and corn syrup.
Simple Sugars: Monosaccharides and
Disaccharides
• The two main types of sugars are
monosaccharides and disaccharides.
• Monosaccharides consist of a single
sugar molecule (“mono” meaning one
and “saccharide” meaning sugar).
• Disaccharides consist of two sugars
chemically joined (“di” meaning two).
Monosaccharides
• The most common monosaccharides in
the human diet are glucose, galactose,
and fructose.
Monosaccharides: The Single Sugars
• Glucose
•
•
•
•
Found in fruits, vegetables, honey
“Blood sugar”—used for energy
Virtually the only fuel used by the brain.
It is the most abundant simple carbohydrate
found in nature.
• It makes up at least 1 of the 2 sugar molecules
in every disacharide.
Monosaccharides: The Single
Sugars
• Fructose
•
•
•
•
Found in fruits, honey, corn syrup
Also called levulose or “Fruit sugar”
Fructose tastes the sweetest of all sugars
Used as a sweetener in foods
Monosaccharides: The Single
Sugars
• Galactose
• Found as part of lactose in milk
• Rarely occurs as a monosaccharide in food
• Chemically bonded to glucose to make lactose
Disaccharides: The Double Sugars
• Disaccharides—two linked sugar units
• Sucrose: glucose + fructose
• “Table sugar”
• Made from sugar cane and sugar beets
• When a label lists sugar as an ingredient, it is referring
to sucrose.
Disaccharides: The Double Sugars
• Lactose: glucose + galactose
• “Milk sugar”
• Found in milk and dairy products
Disaccharides: The Double Sugars
• Maltose: glucose + glucose
• Found in germinating cereal grains
• Product of starch breakdown
• Maltose is fermented in the production of beer
Joining and Cleaving Sugar Molecules
Complex Carbohydrates
• Complex carbohydrates are chains of
more than two sugar molecules.
• Short chains may have as few as three
monosaccharide molecules.
• Long chains (polysaccharides) can
have hundreds or even thousands.
Complex Carbohydrates
• Starch
• Long chains of glucose units
• Amylose–straight chains
• Amylopectin–branched chains
• Found in grains, vegetables, legumes
Complex Carbohydrates
• Glycogen
• Highly branched chains of glucose units
• Body’s storage form of carbohydrate
Oligosaccharides
• Oligosaccharides are short
carbohydrate chains of 3 to 10 sugar
molecules.
• Dried beans, peas, and lentils contain
the two most common ones: raffinose
and stachyose.
Oligosaccharides
• Human milk contains more than 100 different
oligosaccharides.
• Some bind to bacteria to help them pass.
• Some serve as dietary fiber.
• Some assist in brain development.
Polysaccharides
• Polysaccharides are long carbohydrate
chains.
Polysaccharides
• Some form straight chains, while others
branch off in all directions.
• Their configuration makes them either
digestible (starch) or indigestible
(dietary fiber).
Starch
• Plants store energy as starch.
• Dietary sources of starch:
• Grains such as wheat, rice, corn, oats,
millet, and barley.
• Legumes such as peas, beans, and lentils.
• Tubers such as potatoes, yams, and
cassava.
Glycogen
• Animals store carbohydrates in the
form of glycogen.
• It is also called animal starch.
Glycogen
• Glycogen consists of highly branched
chains of glucose.
• Glycogen is stored largely in the
skeletal muscle and liver.
Complex Carbohydrates: Fiber
• Dietary + Functional = Total Fiber
• Indigestible chains of monosaccharides
• Nonstarch polysaccharides: long chains
• Cellulose, hemicellulose, pectins, gums, mucilages
• Lignins
• Found in fruits, vegetables,
grains, legumes
Dietary Fiber
• Soluble fibers dissolve in water.
• Insoluble fibers do not dissolve in
water.
• Soluble fiber from psyllium and oats
has been shown to lower blood
cholesterol levels.
Sources of Dietary Fiber
• Only plant foods contain dietary fiber.
• Soluble fiber is found in oat bran,
legumes, soybean, and some fruits and
vegetables.
• Insoluble fiber is found in wheat bran
and most whole grains.
Carbohydrate Digestion and
Absorption
• Mouth
• Salivary amylase begins digestion of starch
• Small intestine
• Pancreatic amylase completes starch digestion
• Brush border enzymes digest disaccharides
• End products of carbohydrate digestion
• Glucose, fructose, galactose
• Absorbed into bloodstream
• Fibers are not digested, are excreted in feces
Carbohydrates in the Body
• Functions of glucose
•
•
•
•
Energy source
Spares body protein
Prevents ketosis
Excess stored as glycogen
• In liver and muscle
Carbohydrates in the Body:
Regulating Blood Glucose
Carbohydrates in the Diet
• Recommended carbohydrate intake
• AMDR = 45–65% of calories
• Daily Value (for 2,000 kcal) = 300 grams
• Dietary Guidelines
• Variety of grains, fruits, vegetables
• Moderate sugar intake
• Current consumption
Carbohydrates in the Diet
• Increasing
complex
carbohydrate
intake
• Grains,
especially
whole grains
• Legumes
• Vegetables
Whole Kernels
• Germ – the innermost part. Can grow
into a new plant. Rich in protein, oils,
vitamins, and minerals.
• Endosperm – largest middle portion.
High in starch.
Whole Kernels
• Bran – protective coating. Dietary
fibers.
• Husk – inedible covering. Also called
chaff.
Refined Grains
• When grains are refined, the process
removes the outer husk and bran
layers. It sometimes also removes the
inner germ of the grain kernel.
Refined Grains
• This is done when making white flour
from wheat and making white rice from
brown.
Carbohydrates in the Diet
• Moderating sugar intake
• Use less added sugar
• Limit soft drinks, sugary cereals,
candy
• Choose fresh fruits or those canned
in water or juice
Photo © CSquared Studios/Photodisc
Carbohydrates in the Diet
• Nutritive Sweeteners
• Natural v. refined
• Sugar alcohols
• Artificial Sweeteners
•
•
•
•
Saccharin
Aspartame
Acesulfame K
Sucralose
Carbohydrates and Health
• High sugar intake
• Low-nutrient content
• Contributes to tooth decay
• If excess kcal, contributes to obesity
• High fiber intake
•
•
•
•
Better control of blood glucose
Possible reduced cancer risk
Reduced risk of heart disease
Healthier gastrointestinal functioning
An Apple a Day…
• The old adage, “An apple a
day keeps the doctor away”
has persisted over time due
to actual health benefits
from apples.
• Apples have a high pectin
content, a soluble fiber
known to be an effective GI
regulator.
Photo © Photodisc
Cellulose
• Cellulose forms the nondigestible,
fibrous component of plants.
• It is part of grasses, trees, fruits, and
vegetables.
Increasing Fiber Intake
• To increase your fiber intake, eat more
breads, cereals, pasta, rice, fruits,
vegetables, and legumes.
• Eat fruits and vegetables with the peel, if
possible, as this is high in fiber.
• Add fruit to muffins and pancakes.
• Add legumes, such as lentils and pinto, navy,
kidney, and black beans to casseroles.
ADA Position on Nutritive and NonNutritive Sweeteners
• It is the position of the American Dietetic
Association that consumers can safely enjoy
a range of nutritive and non-nutritive
sweeteners when consumed in a diet that is
guided by current federal nutrition
recommendations, such as the Dietary
Guidelines for Americans, and the Dietary
References Intakes, as well as individual
health goals.
Sugar and Children’s Behavior
• In a study designed
to determine
whether or not
sugar truly affects a
child’s behavior, the
results indicated
that dietary sugar
does not cause
adverse behavior.
Photo © Eric Gevaert/ShutterStock, Inc.
Dental Health
• Good dental hygiene,
adequate fluoride, and
proper nutrition help
maintain healthy teeth.
• A well-balanced diet
contains vitamins and
minerals crucial for healthy
bones and teeth.
• To help prevent dental
caries, avoid continuous
snacking on high-sugar
foods.
ADA Position on Health Implications
of Dietary Fiber
• It is the position of the American
Dietetic Association (ADA) that the
public should consume adequate
amounts of dietary fiber in the form of
plant foods.
Effects of Excess Fiber
• With all of its health advantages, high fiber
intake can cause problems, especially in
those who drastically increase their fiber
intake in a short period of time.
• A sudden increase in fiber can cause
increased intestinal gas and bloating.
• If you increase your fiber intake, you should
also increase your water intake to prevent
constipation.
Total Fiber
• Dietary fiber consists of nondigestible
carbohydrates and lignin that are intact and
intrinsic in plants.
• Functional fiber refers to isolated,
nondigestible carbohydrates that have
beneficial physiological effects in humans.
• Total fiber is the sum of dietary fiber and
functional fiber.
Babies and Honey
• Because honey and Karo
syrup may contain spores of
the bacterium Clostridium
botulinum (botulism), they
should never be fed to
infants younger than one
year of age.
• Infants do not produce as
much stomach acid as older
children and adults, which
can allow the spores to
germinate in the GI tract.
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