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

Carbohydrate Is Made by Photosynthesis CHO

Carbohydrate Classifications n Simple CHO = “Sugars” –Monosaccharides: single sugar unit –Disaccharides: two sugar units linked together n Complex CHO= Starch, glycogen, fiber –Polysaccharides: many sugar units linked together

Simple CHO: Sugars n Monosaccharides – – – n Disaccharides – – – –

condensation hydrolysis

Simple Sugars, Cont. n What is sugar good for? n When is sugar considered to be “bad?” – – – –

n 10% recommendation –(current U.S. 24%) n high sugar diet can  change in fat distribution toward central adiposity n binge trigger in some, inhibitor in others – highly individual

Sugar on the Food Label n n n n fructose/levulose n glucose/dextrose n honey/invert sugar n fruit juice concentrate n corn syrup n corn sweetener n molasses n raw sugar n turbinado sugar

Sugar Alcohols n E.g. mannitol, sorbitol, xylitol n Considered “sugar free” sweeteners, but still almost the same kcals as sugar n Sugar free candy -- diarrhea if eaten in excess

A word about lactose: milk sugar and lactose intolerance n Enzyme lactase splits lactose into glu-gal in the small intestine n Lactase deficiency causes trouble digesting milk products – – –

n Different from milk allergy, immune rx to casein n

Carbohydrate Classifications n Simple CHO = “Sugars” –Monosaccharides: single sugar unit –Disaccharides: two sugar units linked together n Complex CHO= Starch, glycogen, fiber –Polysaccharides: many sugar units linked together

Complex CHO: Polysaccharides: Several to Hundreds of ____________ Units Linked Together n Starch – n Glycogen – n Fiber –

Starch n Long straight or branched chains of hundreds of __________________ units n Sources: –Richest source: –Legumes –Tubers

n When eaten, ALL starches are broken down enzymatically to ______________ –(blue dots!) – n One to 4 hours after a meal, all starch  __________________

Glycogen n Storage form of CHO in animals. Not found in diet. n More complex and more highly branched than starch – n Limited capacity for storage –

n Muscle Glycogen – n Liver Glycogen –

Fiber n n Typical U.S. diet: n Most fibers are polysaccharides but –

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

Whole Vs. Refined Grains n Whole grains n Label: n n

n Refined grains n n Label: n Sources: n

“Enriched” n When bran and germ are removed, several vitamins/minerals also n “enriched,” n Shoot for at least half of your grains to be from whole grain sources

Soluble vs. Insoluble fiber n Soluble fiber –foods: barley, fruits (apples), legumes, oats, oat bran, rye, seeds, vegetables, nuts n Health benefits: – –lowers serum cholesterol –stool bulk/softening

n Insoluble fiber –Foods: brown rice/whole grains/wheat bran, fruits, legumes, seeds, veggies n Health benefits: – –Speeds transit through intestines –delayed starch hydrolysis: slowed glu absorption

n If you have a low-fiber diet, add fiber gradually! n n What about fiber supplements? –

Carbohydrates n Digestion and absorption of CHO

Dietary CHO = starch, sugar, and fiber

D&A of CHO n Mouth – – starch Salivary amylase dextrins & maltose glu-glu-glu- glu-glu-glu- glu-glu-glu x100 glu-glu-glu- glu-glu-glu glu-glu

n Stomach – – –Mechanical digestion continues in stomach, but –

n Small Intestine Starch and dextrins Pancreatic amylase maltose glu-glu-glu- glu-glu-glu glu-glu

n Last phase: The brushborder cells of the small intestine. n Enzymes in these cells break down ___________________ to _____________________. maltose lactose sucrose (maltase) (lactase) (sucrase) glu & ________

n Monosaccharides are ABSORBED – – –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) n n n 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? n “Glucose-dependent tissues” rely on glucose for fuel (not fat) –Brain, nervous system, retina, etc. n *** –

n Average person enough CHO stored to last ________________ hours n Since we can’t store much, need to rely on dietary CHO. –