cho and glycemic index

8/12/2019 CHO and Glycemic Index

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IMPORTANCE OF DIETARY CARBOHYDRATES & GLYCEMIC INDEX

CHEMISTRY HHuu mm aa nn ss :: ~ 50% of calories ingested as CHO (10 - 85%)

160 g starch, 120 g sucrose, 30 g lactose, 5 g glucose, 5 g fructose, trace maltoseSOURCES OF CARBOHYDRATE

sucrose : sugar lactose : milk fructose : fruit, corn- syrup processed foods starch (amylose & amylopectin ): wheat, rice, corn, barley, oats, legumes.... glycogen : muscle and liver

GLUCOSE ATP synthesis: all tissues

RBC, tissues of eye, renal medulla, brain, intestines, white blood cells, skin: relyprimarily on glucose as energy source in the fed state

In the fed state, glucose is primarily obtained from dietary carbohydrate (CHO)

Monosaccharides:Glucose, fructose, galactose

Dissacharides:maltose: glucose + glucoselactose: glucose + galactosesucrose: glucose + fructose

Polysaccharides:amylose: glucose + glucose +.... (linear)amylopectin: glucose + glucose +.... (branched)glycogen: glucose + glucose +...( very branched )

GENERAL FUNCTIONS OF CARBOHYDRATES Energy: ATP synthesis (~ 4 kcal/g) NEAA synthesis: carbon skeleton Fat synthesis: via acetyl-CoA Glycogen synthesis TCA cycle intermediates Nucleotides: sugar portion Glycoproteins Glycolipids


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ESSENTIALITY OF CARBOHYDRATES metabolic need is for glucose: ~300 g/d in humans

glucose can be made from most AAs (not Leu) glucose can be made from propionate (SCFA) glucose can be made from glycerol glucose cannot be made from fatty acids CHO not strictly essential in diet Relying solely on AAs etc. as precursor for glucose not prudent or practical (except

for carnivores), so......

DIGESTION, ABSORPTION & TRANSPORT into cellsMouth salivary amylase :

- hydrolyzes 1-4 bonds in starch- release: psychic (cephalic) stimuli

mechanical stimuli : food in mouth chemical stimuli : food on taste buds little digestion

Stomach : Negligible


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GLUCOSE METABOLISM: GLUCOSE DISPOSAL & SYNTHESIS

SIGNIFICANCE Control blood glucose concentrations in starvation, exercise, stress, refeeding...

4 - 6 mmol/L (humans): 10 mM after meal high blood sugar: damage lens, kidney etc. complications of diabetes low blood glucose: brain damage & death Control rate of glucose utilization in tissues

FACTORS AFFECTING GLUCOSE CONCENTRATIONTend to raise

Hunger Glucose absorption from gut Hepatic glycogenolysis

Adrenaline Glucagon

Gluconeogenesis in liver Insulin antagonist

Growth Hormone Cortisol

Insulin destroying enzymesTend to lower


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Satiety Glucose diffusion in ECF Muscular exercise Insulin

Glucose oxidation

Glycogen deposition Lipogenesis Gluconeogenesis

{ glucosuria in diabetes}


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FIBER SOURCES Plant material plant cell wall : 95% of fibre cementing material in plants legumes: beans, peas

forages: alphalpha, timothy hay.... bran of cereals: wheat, oats, corn, rice.... skin of fruits & vegetables

PHYSIOLOGICAL & METABOLIC EFFECTS

Adsorption or binding of nutrients by fibre- lignin, pectin, -glucan can bind some nutrientsbind and reduce absorption of bile acids

cholesterol used for more bile acid synthesislower serum cholesterol

reduce Ca 2+ , Fe 2+ , Zn 2+ absorptionCOO - bind divalent cationspectins, hemicellulose


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SIGNIFICANCE

Fiber is not inertEnergy (< 4 kcal/g but > 0 kcal/g)Disease prevention & treatment

constipation/ hemorrhoids/ appendicitisheart disease/ plasma cholesteroladult-onset diabetes/ glucose absorptionobesity/ satiety

Mineral deficiencyrare: intake low and fibre/phytate high

THE GLYCEMIC INDEX (GI)Used in addition to carbohydrate counting to fine tune blood glucose management

Measures how a food affects blood glucose levels

Three levels of the GI include: high, medium, and low

Using GI to plan meals involves choosing medium or low GI foods or combininghigh GI foods with low GI foods to balance blood glucose levels

Foods are ranked based on how they compare to a reference food, such as whitebread or glucose

HIGH GLYCEMIC INDEX (>70) Baked potato French fries Rice cakes Bagels Graham crackers Refined cereal products Sugar-sweetened beverages Jelly beans Candy bars Couscous Cranberry juice cocktail White basmati rice White-flour pasta


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MEDIUM GLYCEMIC INDEX (56-69) Orange juice Popcorn Corn Sweet potato Peas Brown/white rice Oatmeal Bulgur Whole grain breads Whole grain pasta No-sugar added fruitjuices

LOW GLYCEMIC INDEX (

cho and glycemic index

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