Carbohydrates Part One: A. Classification B. Digestion & Absorption of CHO

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

Complex CHO= Starch, glycogen, fiber– Polysaccharides: many sugar units linked

together

Simple CHO: Sugars Monosaccharides

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Disaccharides

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condensation

hydrolysis

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

Sugar on the Food Label

fructose/levulose glucose/dextrose honey/invert sugar

fruit juice concentrate corn syrup corn sweetener molasses raw sugar turbinado sugar

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

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

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

Starch –

Glycogen –

Fiber –

Starch Long straight or branched chains of

hundreds of __________________ units Sources:

– Richest source:

– Legumes

– Tubers

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 Storage form of CHO in animals. Not

found in diet. More complex and more highly branched

than starch–

Limited capacity for storage–

Muscle Glycogen–

Liver Glycogen–

Fiber

Typical U.S. diet:

Most fibers are polysaccharides but–

Most common fibers: cellulose, hemicellulose, and pectin. Also gums, mucilages, and lignins

Sources:

Whole Vs. Refined Grains Whole grains Label:

Refined grains Label:

Sources:

“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

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

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

If you have a low-fiber diet, add fiber gradually!

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

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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

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

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 & ________

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.

Large Intestine (colon)

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?

“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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