carbohydrates part one: a. classification b. digestion & absorption of cho
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Carbohydrates
Part One:
A. Classification
B. Digestion & Absorption of CHO
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Carbohydrate Is Made by Photosynthesis
CHO
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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
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Simple CHO: Sugars Monosaccharides
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Disaccharides
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condensation
hydrolysis
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Simple Sugars, Cont. 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
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Sugar on the Food Label
fructose/levulose glucose/dextrose honey/invert sugar
fruit juice concentrate corn syrup corn sweetener molasses raw sugar turbinado sugar
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Sugar Alcohols
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
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A word about lactose: milk sugarand lactose intolerance
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
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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
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Complex CHO: Polysaccharides:Several to Hundreds of ____________ Units Linked Together
Starch –
Glycogen –
Fiber –
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Starch 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 __________________
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Glycogen Storage form of CHO in animals. Not
found in diet. More complex and more highly branched
than starch–
Limited capacity for storage–
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Muscle Glycogen–
Liver Glycogen–
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Fiber
Typical U.S. diet:
Most fibers are polysaccharides but–
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Most common fibers: cellulose, hemicellulose, and pectin. Also gums, mucilages, and lignins
Sources:
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Whole Vs. Refined Grains Whole grains Label:
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Refined grains Label:
Sources:
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“Enriched” 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
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Soluble vs. Insoluble fiber Soluble fiber
– foods: barley, fruits (apples), legumes, oats, oat bran, rye, seeds, vegetables, nuts
Health benefits: –
– 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 Health benefits:
– – Speeds transit through intestines
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– delayed starch hydrolysis: slowed glu absorption
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If you have a low-fiber diet, add fiber gradually!
What about fiber supplements?
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Carbohydrates
Digestion and absorption of CHO
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Dietary CHO = starch, sugar, and fiber
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D&A of CHO Mouth
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starch Salivary amylase dextrins & maltose
glu-glu-glu-glu-glu-glu-glu-glu-glu x100
glu-glu-glu-glu-glu-glu
glu-glu
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Stomach –
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–Mechanical digestion continues in stomach, but
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Small Intestine
Starch and dextrins
Pancreatic amylasemaltose
glu-glu-glu-glu-glu-glu
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
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– ____________ then regulates the release of glu back into the bloodstream for transport to tissues.
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Large Intestine (colon)
Fiber – (absorbed & used for E, 0-2kcals/g of
fiber)
– (Cellulose and lignin completely pass through in feces)
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So now we have glucose in the liver and the bloodstream. If glu is to fuel the tissues, how is it done?
“Glucose-dependent tissues” rely on glucose for fuel (not fat) – Brain, nervous system, retina, etc.
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Average person enough CHO stored to last ________________ hours
Since we can’t store much, need to rely on dietary CHO.
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