Carbohydrates

Carbohydrates

2

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

3

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

4

Carbohydrates

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

– Monosaccharides and Disaccharides• Polysaccharides (more complex)

– Starch, Glycogen, and Fiber

5

6

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

7

8

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

9

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

10

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

11

12

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

13

14

Carbohydrates in Foods

• Starch• Fiber• Nutritive Sweeteners

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

15

16

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

17

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

18

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)

19

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

20

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

21

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

22

23

Carbohydrate Digestion

• Mouth– Salivary amylase begins digestion

• Small intestine– Specific enzymes break down disaccharides

• Maltase: maltose; sucrase: sucrose; lactase:lactose– Fiber not broken down

24

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)

25

26

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?

27

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

28

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

29

30

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

31

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

32

33

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

34

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