The Carbohydrates
Simple sugars, complex
carbohydrates,
and fiber.
Carbohydrates
• Body’s preferred source of energy
– Cells of body use the carb. Glucose
• Most food sources of carbohydrates are plant
sources
– Why?
– One animal source of carbs
Classifying Carbohydrates
• Simple Sugars
– Monosaccharides
– Disaccharides
• Complex Carbohydrates
– Starch
– Glycogen
– Cellulose (a form of fiber)
Carbohydrate Intake
• Recommended intake of carbohydrate
– 45-65 % daily kcal should come from
carbohydrates
– RDA ~130 g carbohydrate/day
– Maximum 25% daily kcal from added sugars
• ~500 kcal/day
• Controversial with nutritionists
• WHO recommends a maximum of 10% daily kcal from
simple sugars
Fiber Intake
• General recommendations:
– 25g (women) - 38 g (men) fiber/day
– Amount recommended drops after age 50 to:
• 21 g (women) - 30 g (men) fiber/day
– Maximum intake recommended: ~40 g/day
• Why is too much not a good thing?
Evaluating Your Intake
• Intake Goals:*
– 45-65 % daily kcal from carbohydrate
• Select primarily from complex carbohydrates
– Make half of the complex carbohydrates whole grains
– Limit added sugars
– 25-38 g fiber/day or 21 – 30 g fiber/day of over
50.
• max 40 g/day
– *Computer programs may suggest different values
Carbohydrates
• All nutritionally important sugars are hexose
sugars
– Hexose =
– All hexose sugars have the same chemical formula
Simple Carboydrates

Monosaccharides – C6H12O6
◦ Glucose
◦ Fructose
◦ Galactose
Glucose, fructose and galactose all have the
same chemical composition, but they very
different properties!
 Why?
Glucose
Glucose
– Also called  dextrose
– Sugar to which all others are converted after
absorption
• Occurs in the liver
– Cell’s preferred source of energy
• Under most conditions the brain requires glucose as an
energy source
– Natural food sources of glucose are limited.
• Honey contains glucose
Fructose
– Also called fruit sugar
– Sweetest of all the carbohydrates
– Sources
• Fruits
• Honey
• Added - High fructose corn-syrup is often used to
sweeten foods
– Too much fructose can draw water into GI tract
and cause GI distress
Galactose
– Not very sweet
– Not found naturally in many foods
– Found in “lactaid” milk
Disaccharides
• Disaccharides are made by joining two
monosaccharides by a chemical bond
Disaccharides
• There are three disaccharides:
– Sucrose
– Maltose
– Lactose
• Glucose is a component of each disaccharide.
Disaccharides
• 3 disaccharides
– Sucrose = glucose--fructose
– Maltose = glucose--glucose
– Lactose = glucose--galactose
Chemical bond
Disaccharides
• Maltose = glucose-____________
– Not in many foods
• Made when starch breaks down
• Find some in barley
• Made during fermentation – alcohol synthesis
Disaccharides
• Maltose digestion occurs in the SI
– Digestion breaks the bond between the glucose
molecules.
• Requires the presence of the SI enzyme maltase.
• maltose  _________ + ___________
• Absorption
Disaccharide Digestion
maltase
Disaccharides
• Sucrose = glucose-____________
– Table sugar
– Made from sugar beets and sugar cane
– Fairly sweet
• Food sources
Disaccharides
• Sucrose digestion occurs in SI
– Enzyme needed = sucrase
– Sucrose  _________ + __________
• Absorption
Disaccharides
• Lactose = glucose- ___________
• Also called milk sugar
• Food Sources
– Milk
– Ice cream, sherbet
– Smaller amounts in cheese and yogurt
Disaccharides
• Lactose digestion in SI
– Enzyme required is lactase
– Lactose  glucose + ___________
• Absorption
Lactose Intolerance
• Who in class is lactose intolerant?
Populations at greatest risk:
Asian - ~ 80%
African descent - ~ 75%
Hispanic -~ 50%
Native Americans - ~ 80%
Lactose Intolerance
• Some refer to this as lactose maldigestion
• Biological cause of lactose intolerance
– SI does not make enough (or any) lactase
– As a result the lactose is not digested
• Undigested lactose cannot be absorbed
– Amount of lactase made decreases in many
people as they age
Symptoms of Lactose Intolerance
• Undigested lactose:
• Draws water into GI tract
– Results in bloating, diarrhea, cramps
• Metabolized by bacteria in the colon
– Bacteria thrive and make gases and acids
» These add to the GI distress
Managing Lactose Intolerance
Limit intake of milk products
◦ Includes: milk, ice cream, cottage cheese, sherbet,
yogurt with added milk solids

To limit the amount of lactose in GI tract at any time
◦ Ingest milk products with other foods
◦ Spread intake over the day
Managing Lactose Intolerance
• Many can eat:
– Hard cheeses
• Cheese making process removes much of lactose
• Lactose levels decrease as cheeses age
– Yogurt and kefir – fermented milk products
• Fermentation process breaks down much of the lactose
– Lactase treated milks – Lactaid milk
Monosaccharide- Summary
• Monosaccharrides are single sugars
– All isomers of C6H12O6
– Glucose serves as the essential energy source, and is
commonly known as blood sugar or dextrose.
– Fructose is the sweetest, occurs naturally in honey and
fruits, and is added to many foods in the form of highfructose corn syrup.
– Galactose rarely occurs naturally as a single sugar.
Disaccharide - Summary
• Disaccharides are pairs of monosaccharides, one of
which is always glucose
– Condensation reactions link monosaccharides together.
– Hydrolysis reactions split molecules and commonly occur during
digestion.
– Maltose consists of two glucose units. It is produced during the
germination of seeds and fermentation.
– Sucrose is fructose and glucose combined. It is made from sugarcane
and sugar beets, and tastes sweet.
– Lactose is galactose and glucose combined. It is found in milk and milk
products.
© 2008 Thomson - Wadsworth
Polysaccharides
• All polymers of glucose
• We will consider:
– Glycogen
– Starch
– Cellulose
Polysaccharides
• Polysaccharides differ in:
– Function and sources
– # glucose
– Type of bonding between glucose
– Incidence of branching or coiling
Polysaccharides
• Glycogen
– Function: animal storage form of glucose
– Found, made, and used in:
• Liver …….
• Muscle cells ….
– Stores …..
Polysaccharides
• Structure of glycogen
– ~ million glucose joined by alpha glycosidic bonds
– Highly branched
• Branch every 5-6 glucose
• Why branching is important
– Food sources: none
• We make glycogen from extra glucose
Starch – Complex Carbohdrate
• Function: plant storage form of glucose
– All food sources of starch are plant sources
• Goal is for the majority of the carbohydrates
in your diet to be from starch
– Starch rich foods include:
Starch
• Structure of starch
– ~ 100,000 glucose joined by alpha glycosidic
bonds
– Two Forms
• Branched form - amylopectin
– branches every ~20 glucose
• Coiled form - amylose
Starch
• Starch digestion and absorption
– Mouth
– Stomach
– SI
Polysaccharides
• Cellulose
– Function: structural component of all plant cells
– Structure
• Many glucose bonded by beta glycosidic bonds
– We do not have the enzymes needed to digest beta bonds in
cellulose
• Long, unbranched chains that coil around each other to
form fibers
– Very strong
Polysaccharides
• Cellulose
– One of the polysaccharide fibers
• We do not have the enzymes needed to digest the
bonds in fibers.
Fiber
• Structural components of plants we cannot
digest
• Classes of fibers:
– Cellulose and hemicellulose
– Pectins
– Gums and mucilages
– Lignins
Another way to classify fibers
• Soluble fibers – viscous, fermentable by
bacteria
– Gums, mucilages, pectins, some hemicellulose
– Food sources
• Fruits
• Oat bran, Legumes
• Insoluble fibers – nonviscous, not digested by
intestinal bacteria
– Cellulose and lignins
– Wheat bran, corn, rye, most vegetables…
Functional Fibers
• Soluble fibers help lower cholesterol levels
• How?
– Soluble fibers bind/trap bile in the SI
– As a result the bile is excreted and not recycled
• Bile is made from cholesterol
– Therefore, the liver uses cholesterol to make more
bile
• This lowers cholesterol levels
Benefits of fiber in diet
• Promotes bowel health
– Reduces risk of diverticulitis/osis and appendicitis
– Softens stools (keeps you regular)
– ?? Decreased risk colon cancer
• Soluble fiber reduces cholesterol levels
Diverticular Disease
Benefits of fiber in the diet
•
Slows gastric emptying time
–
–
Aids in weight control – feel full longer
Aids in management of diabetes
•
•
Fiber slows the absorption of glucose and reduces spikes in
blood glucose levels
Adds in weight control
–
Fiber adds bulk w.o. kcal
Fiber
• Adding fiber to the diet
– Add slowly
– Increase water intake
• Food sources:
approximate fiber level
– Whole grain breads and cereals: 1-2g/serving
• Higher level in many cereals
–
–
–
–
Vegetables: 2-3 g/serving
Legumes: 5-8 g/serving
Fruits with skins: 2 g/serving
Dried fruit: 2-3 g/serving
© 2008 Thomson - Wadsworth
Too much fiber in the diet
• Harmful effects of excessive fiber intake
• Displaces energy and nutrient-dense foods from the
diet
– Bulk without nutrients
• Abdominal discomfort, bloating, and gas from
fermentable fibers
• May interfere with nutrient absorption
Sugar and Health
• Many high sugar foods are a source of empty
calories
• All carbohydrates increase risk of dental caries
(cavities)
– Longer the sugar/starch is on the teeth the greater
the risk
Sugar Myths
• Sugar and:
– Obesity
• Extra/empty calories from sugar are converted to fat
and can contribute to obesity
– Heart disease
• High sugar diets have been shown to alter blood lipid
levels
– Hyperactivity
– Criminal behavior
Carbohydrate
Digestion in
the GI Tract
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Alternatives to Sugar
© 2008 Thomson - Wadsworth
Artificial Sweeteners
• Also called nonnutritive sweeteners
– Saccharin
• Used primarily in soft drinks and as a tabletop
sweetener
• Rapidly excreted in the urine
• Does not accumulate in the body
• Has been removed from list of cancer-causing
substances
© 2008 Thomson - Wadsworth
Artificial Sweeteners
• Aspartame
– General purpose sweetener
– Warning about phenylalanine for those with PKU
– Controversial finding that aspartame may have
caused cancer in rats
– Excessive intake should be avoided by those with
epilepsy
© 2008 Thomson - Wadsworth
Artificial Sweeteners
• Acesulfame-K (acesulfame potassium)
– Research confirms safety
• Sucralose
– Made from sugar
– Passes through digestive tract
• Neotame
– Most recent on the market
– Very sweet
– Phenylalanine not an issue
© 2008 Thomson - Wadsworth
Artificial Sweeteners
• Tagatose
– Used for foods and beverages
– Provides less kcalories than sugar
– High doses can cause flatulence and loose stools.
• Alitame and Cyclamate
– Pending FDA approval
– Approved in other countries
© 2008 Thomson - Wadsworth
Stevia – An Herbal Alternative
• Lacks research
• Classified as a dietary supplement
• Not required to have testing and FDA approval
© 2008 Thomson - Wadsworth
Sugar Replacers
• Also called nutritive sweeteners, sugar
alcohols, and polyols
• Maltitol, mannitol, sorbitol, xylitol, isomalt,
and lactitol
• Absorbed more slowly and metabolized
differently in the body
• Low glycemic response
• Side effects include GI discomfort
© 2008 Thomson - Wadsworth
© 2008 Thomson - Wadsworth