Carbohydrates

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Learning Outcomes

• Identify the major types of carbohydrates and give examples of food sources for each

• List alternative sweeteners that can be used to reduce sugar intake

• Describe recommendations for carbohydrate intake and health risks caused by low or excessive intakes

• List the functions of carbohydrates in the body

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Learning Outcomes

• Explain how carbohydrates are digested and absorbed

• Explain the cause of, effects of and dietary treatment for lactose intolerance

• Describe the regulation of blood glucose, conditions caused by blood glucose imbalance, types of diabetes, and dietary treatment for diabetes

• Describe dietary measures to reduce the risk of developing type 2 diabetes

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Carbohydrates

• Composed of carbon, hydrogen and oxygen• Produced by plants via photosynthesis• Simple carbohydrates

– Monosaccharides and Disaccharides

• Polysaccharides (more complex)– Starch, Glycogen, and Fiber

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Monosaccharides

– Glucose• Blood sugar

– Fructose• High-fructose corn syrup

– Galactose• Part of lactose

– Sugar Alcohols (monosaccharide derivatives)• Xylitol, mannitol and sorbitol

– Pentoses (5 carbon)• Ribose and Deoxyribose

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Disaccharides

• Two monosaccharides linked by a condensation reaction– Alpha or beta C-O-C bonds connect them

• Maltose– Glucose and Glucose; alpha bond

• Sucrose– Glucose and Fructose; alpha bond

• Lactose– Galactose and Glucose; beta bond

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Complex Carbohydrates

• Oligosaccharides– Contain 3-10 sugar units– Raffinose and Stachyose– Indigestible; bacterial fermentation – gas

• Polysaccharides– Contain many glucose molecules– Alpha or beta bond determine digestibility

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Digestible Polysaccharides

• Starch (plants)– Amylose: straight chain– Amylopectin: branched

• Glycogen (animals)– Storage form of glucose in human body– Liver glycogen (90g): converted to blood sugar– Muscle glycogen (300g): glucose for muscle use

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Indigestible Polysaccharides

• Total Fiber– Dietary Fiber + Functional Fiber

• Soluble Fibers– Pectin, gum, mucilages and some hemicelluloses

• Insoluble Fibers– Cellulose, hemicelluloses and lignin

• Health benefits of fibers

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Carbohydrates in Foods

• Starch• Fiber• Nutritive Sweeteners

– Mono and disaccharides– High fructose corn syrup– Sugar alcohols

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Alternative (Non-Nutritive) Sweeteners

• Yield no energy• Acceptable Daily Intake (ADI)• Saccharin

– Oldest alternative sweetener, – Develops bitter taste with cooking

• Aspartame– Cannot be used in cooking– Contains phenyalanine

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Alternative Sweeteners• Neotame

– Similar to aspartame but not digested• Acesulfamine K

– Can be used in cooking• Sucralose

– Made from sucrose-can be used in cooking• Tagatose

– Isomer of fructose, pre-biotic• Stevia

– Recently approved by FDA for use in beverages– Sold as dietary supplement

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Recommended Intake of Carbohydrates

• RDA-130 grams• 45%-65% of total energy needs• Limit added sugars and caloric sweeteners• Fiber: 14g/1000kcal is adequate intake

– 25g/d - women under 50 (21g/d after 51)– 38g/d - men under 50 (30g/d after 51)

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Our Carbohydrate Intake• 50% of total energy needs• Added sugars 16% of kcal

– Recommendations:• 6% of kcal (Dietary Guidelines)• 10% of kcal (WHO)• 25% of kcal (DRIs)

• Dietary fiber• 25-50% less than recommended• Average intake-1 fruit and 1 or fewer whole grain

servings

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Functions of Digestible Carbohydrates in the Body

• Provide energy: 4 kcal/g• Spare protein

– Body does not utilize gluconeogenesis

• Prevent ketosis– Incomplete breakdown of fatty acids

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Functions of Indigestible Carbohydrates in the Body

• Promoting bowel health– Constipation and hemorrhoids– Diverticulosis and diverticulitis

• Reducing obesity risk– Fullness and satiety

• Enhancing blood glucose control– soluble fibers

• Reducing cholesterol absorption– soluble fibers

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Carbohydrate Digestion

• Mouth– Salivary amylase begins digestion

• Small intestine– Specific enzymes break down disaccharides

• Maltase: maltose; sucrase: sucrose; lactase:lactose

– Fiber not broken down

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Carbohydrate Absorption

• Active absorption: Glucose and Galactose • Facilitated absorption: Fructose• Liver converts fructose and galactose to

glucose• Blood glucose used by cells• Glucose storage: muscle and liver glycogen• Excess glucose: converted to fat by liver

(stored in adipose tissue)

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Health Concerns Related to Carbohydrate

• Very High Fiber Diets (above 50-60 grams)– High fiber + low fluid = constipation,

hemorrhoids, blockage– Decrease absorption of certain minerals

• High Sugar Diets– Increase risk of weight gain and obesity– Increase risk of dental caries– Cardiovascular disease?

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Health Concerns Related to Carbohydrate

• Lactose Intolerance– Primary

• Decreased lactase production– Secondary

• Associated with disease that damage the lactase- producing cells

• Glucose Intolerance– Hypoglycemia– Hyperglycemia

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Regulation of Blood Glucose• Normal concentration: 70-100mg/dL

– Regulated by liver

• Insulin (pancreas)• Hormone that facilitates transfer of glucose from

blood into cells– Lowers blood glucose

• Glucagon, Cortisol, Epinephrine, Norepinephrine and Growth Hormone – Raise blood glucose

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Other Blood Sugar Disorders

• Metabolic Syndrome– Group of factors that increase risk for Type 2

diabetes and cardiovascular disease

• Hypoglycemia– Reactive Hypoglycemia

• Exaggerated insulin response after eating

– Fasting Hypoglycemia• Low blood sugar after fasting

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Glycemic Index and Glycemic Load

Glycemic Index (GI)• Ratio of the blood glucose response to a

given food, compared with a standard• Influenced by many factors• Based on a 50g carbohydrate serving

Glycemic Load• Amount of carbohydrate in consumed food

multiplied by GI and divided by 100• Better reflects a food’s effect on blood

glucose than GI alone

Medical Perspective

Diabetes Mellitus

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Type 1 Diabetes Mellitus

• Insulin producing cells in pancreas are destroyed (autoimmune disease)– Insulin therapy required for life

• Diet must be coordinated with insulin– Exchange system, carbohydrate counting

• Increased risk for cardiovascular disease, blindness and kidney disease

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Type 2 Diabetes Mellitus

• Progressive disease• Characterized by insulin resistance

– Insulin production may be low, normal, or high

• Most common type of diabetes (90% of cases)• Treatment:

– Diet– Physical activity– Medications