Chapter 002

Williams' Basic Nutrition & Diet Therapy

Chapter 2

Carbohydrates

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14th Edition

Lesson 2.1: Carbohydrates: Energy Source, Their Structures, Role as Fiber

1. Carbohydrate foods provide practical energy sources because of their availability, relatively low cost, and storage capability.

2. Carbohydrate structures vary from simple to complex, providing both quick and extended energy for the body.

3. Dietary fiber, an indigestible carbohydrate, serves separately as a regulatory agent within the gastrointestinal tract.

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Nature of Carbohydrates (p. 13)

Relation to energy Basic fuel source Energy production system Dietary importance

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Classes of Carbohydrates (p. 14)

Monosaccharides Glucose: basic single sugar in human metabolism Fructose: primarily found in fruits and honey Galactose: product of lactose digestion

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Classes of Carbohydrates (cont’d) (p. 15)

Disaccharides Sucrose: common table sugar Lactose: sugar found in milk Maltose: product of intermediate breakdown of

starch by the body

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Classes of Carbohydrates (cont’d) (p. 16)

Polysaccharides Complex carbohydrates Composed of many single-sugar units

• Starch: most significant polysaccharides• Glycogen: formed within body tissues; crucial• Dietary fiber: important dietary assets

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Dietary Fiber (p. 17)

Whole grains Legumes Vegetables Fruits with as much skin remaining as possible

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Dietary Fiber (cont’d) (p. 17)

Health organizations emphasize role of dietary fiber Recommended daily intake for men age 50 and

younger: 38 g/day For women: 25 g/day Increases should be gradual

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Case Study

M.H., a 45-year-old female, has made a nutrition goal to increase her intake of dietary fiber to 25 grams per day.

She comes for nutrition counseling on food suggestions to assist her in being successful.

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Case Study (cont’d)

Before going further with M. H. in giving suggestions for increasing fiber intake in the diet, what questions may you need to investigate?

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Case Study: Recommendations for Intake

After reviewing M.H.’s fiber intake for a typical day, you find that she consumes less than half of the recommended intake for women of 25 grams per day.

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Case Study: Follow-Up on Fiber Intake

M.H. returns for a follow-up visit to make sure she is following the suggested recommendations for increasing fiber intake.

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Cellulose (p. 17) Cellulose: chief component of cell walls in

plants Lignin

Only noncarbohydrate dietary fiber Large compound, forms woody part of some

plants Noncellulose polysaccharides

Absorb water and swell to larger size, slowing stomach emptying

Bind with bile acids Provide bulk for normal muscle action

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Other Sweeteners (p. 20)

Nutritive sweeteners Sugar alcohols (sorbitol, mannitol, xylitol)

Nonnutritive sweeteners Artificial sweeteners in food

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Functions of Carbohydrates(p. 21)

Primary energy function Basic fuel supply

• Physical activities• Work of body cells

Reserve fuel supply• Liver stores about 100 g of glycogen• Muscle stores 300-400 g• Maintains blood glucose level

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Other Sweeteners (cont’d) (p. 22)

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Functions of Carbohydrates (cont’d) (p. 21)

Primary energy function (cont’d) Special tissue functions

• Liver: Glycogen reserves maintain overall energy balance

• Carbohydrate protects protein and fat supply • Central nervous system depends on constant

carbohydrate supply

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Food Sources of Carbohydrates (p. 22)

Starches Most important carbohydrate in the diet Whole-grain starches such as rice, wheat, corn,

potatoes Sugars

Not necessarily bad Added sugars provide empty calories Moderation is key

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Digestion of Carbohydrates (p. 24)

Mouth Mechanical or muscle functions break food mass

into smaller particles Chemical process in which enzymes begin

breaking food down Stomach

Peristalsis continues mechanical breakdown Gastric secretions continue chemical breakdown

of nutrients Secretions do not break down carbohydrates but

stop action of salivary amylase

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Digestion of Carbohydrates (cont’d) (p. 25)

Small intestine Peristalsis continues mechanical breakdown of

food Enzymes from pancreas and intestine continue

chemical breakdown

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Digestion of Carbohydrates (cont’d) (p. 26)

Pancreatic secretions Enter duodenum through common bile duct Contain pancreatic amylase to continue

breakdown of starch Intestinal secretions

Three disaccharidases: sucrose, lactase, maltase Render disaccharides into monosaccharides

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Recommendations for Dietary Carbohydrate (p. 26)

Dietary Reference Intakes 45% to 65% of adult’s total caloric intake should

come from carbohydrate foods Limit sugar to no more than 25% of calories

consumed Dietary Guidelines for Americans, 2010

Does not provide a specific caloric number or percentage, but does provide recommendations

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