Carbohydrates
Part One:
A. Classification
B. Digestion & Absorption of CHO
Carbohydrate Is
Made by
Photosynthesis
CHO
Carbohydrate Classifications

Simple CHO = “Sugars”
– Monosaccharides: single sugar unit
– Disaccharides: two sugar units linked
together
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Complex CHO= Starch, glycogen, fiber
– Polysaccharides: many sugar units linked
together
Simple CHO: Sugars
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Monosaccharides
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Disaccharides
–
–
–
–
condensation
hydrolysis
Simple Sugars, Cont.
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What is sugar good for?
When is sugar considered to be “bad?”
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10% recommendation
– (current U.S. 24%)
high sugar diet can change in fat
distribution toward central adiposity
binge trigger in some, inhibitor in others –
highly individual
Sugar on the Food Label
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fructose/levulose
glucose/dextrose
honey/invert sugar
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fruit juice concentrate
corn syrup
corn sweetener
molasses
raw sugar
turbinado sugar
Sugar Alcohols
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E.g. mannitol, sorbitol, xylitol
Considered “sugar free” sweeteners,
but still almost the same kcals as sugar
Sugar free candy -- diarrhea if eaten in
excess
A word about lactose: milk sugar
and lactose intolerance
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Enzyme lactase splits lactose into glu-gal in the
small intestine
Lactase deficiency causes trouble digesting
milk products
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Different from milk allergy, immune rx to
casein
Carbohydrate Classifications

Simple CHO = “Sugars”
– Monosaccharides: single sugar unit
– Disaccharides: two sugar units linked
together

Complex CHO= Starch, glycogen,
fiber
– Polysaccharides: many sugar units
linked together
Complex CHO: Polysaccharides:
Several to Hundreds of ____________ Units
Linked Together
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Starch –
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Glycogen –
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Fiber –
Starch
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Long straight or branched chains of
hundreds of __________________ units
Sources:
– Richest source:
– Legumes
– Tubers
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When eaten, ALL starches are broken
down enzymatically to ______________
– (blue dots!)
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One to 4 hours after a meal, all starch 
__________________
Glycogen
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Storage form of CHO in animals. Not
found in diet.
More complex and more highly branched
than starch
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Limited capacity for storage
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Muscle Glycogen
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Liver Glycogen
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Fiber
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Typical U.S. diet:
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Most fibers are polysaccharides
but
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Most common fibers: cellulose,
hemicellulose, and pectin. Also gums,
mucilages, and lignins
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Sources:
Whole Vs. Refined Grains
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Whole grains
Label:
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Refined grains
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Label:
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Sources:
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“Enriched”
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When bran and germ are removed,
several vitamins/minerals also
“enriched,”
Shoot for at least half of your grains to
be from whole grain sources
Soluble vs. Insoluble fiber
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Soluble fiber
– foods: barley, fruits (apples), legumes, oats,
oat bran, rye, seeds, vegetables, nuts
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Health benefits:
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– lowers serum cholesterol
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– stool bulk/softening
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Insoluble fiber
– Foods: brown rice/whole grains/wheat
bran, fruits, legumes, seeds, veggies
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Health benefits:
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– Speeds transit through intestines
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•
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– delayed starch hydrolysis: slowed glu
absorption
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If you have a low-fiber diet, add fiber
gradually!
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What about fiber supplements?
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Carbohydrates
Digestion
and absorption of CHO
Dietary CHO = starch, sugar, and fiber
D&A of CHO
 Mouth
–
–
starch
glu-glu-gluglu-glu-gluglu-glu-glu
x100
Salivary amylase
dextrins & maltose
glu-glu-gluglu-glu-glu
glu-glu
 Stomach
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–Mechanical digestion continues
in stomach, but
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 Small
Starch
and
dextrins
glu-glu-gluglu-glu-glu
Intestine
Pancreatic amylase
maltose
glu-glu
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Last phase: The brushborder cells of
the small intestine.
Enzymes in these cells break down
___________________ to
_____________________.
maltose
lactose
sucrose
(maltase)
(lactase)
(sucrase)
glu & ________
glu & ________
glu & ________
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Monosaccharides are ABSORBED
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– In liver, fru and gal are converted to glu
•
– ____________ then regulates the release
of glu back into the bloodstream for
transport to tissues.
Large Intestine (colon)
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Fiber 
– (absorbed & used for E, 0-2kcals/g of
fiber)
– (Cellulose and lignin completely pass
through in feces)
So now we have glucose in the liver and the
bloodstream. If glu is to fuel the tissues, how is it
done?
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“Glucose-dependent tissues” rely on
glucose for fuel (not fat)
– Brain, nervous system, retina, etc.
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***
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Average person enough CHO stored to
last ________________ hours
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Since we can’t store much, need to
rely on dietary CHO.
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