the carbohydrates: sugars, starches, and fibers

The The Carbohydrates: Carbohydrates:

Sugars, Starches, Sugars, Starches, and Fibersand Fibers

Chapter 4Chapter 4

Chapter 4 ObjectivesChapter 4 Objectives

1. Identify the monosaccharides, disaccharides, and polysaccharides common in nutrition by their chemical structures and major food sources.

a. Classify carbohydrates as mono-, di-, or polysaccharides.

b. Explain the two major types of dietary fibers and their uses in the body.

2. Summarize carbohydrate digestion and absorption. a. Trace the digestion and absorption of carbohydrates.

b. List the enzymes used in the digestion of carbohydrates.

c. Describe lactose intolerance symptoms, prevalence, and treatment.

3. Explain how the body maintains its blood glucose concentration and what happens when blood glucose rises too high or falls too low.

a. List the major uses of glucose in the body.

b. Discuss the hormones used by the body to maintain normal blood glucose concentration.

c. List the major types of diabetes.

d. Explain glycemic load and the pros and cons of its use in meal planning.

4. Describe how added sugars can contribute to health problems. a. Identify the major sources of added sugars in the diet.

b. Describe the effect of added sugars on dental health.

c. List the common alternatives to sugar in the diet.

5. Identify the health benefits of, and recommendations for, starches and fibers. a. Identify the health benefits of a diet rich in starch and fiber.

b. Identify the Daily Value and DRI for fiber and methods to increase fiber in the diet.

IntroductionIntroduction

• Brain• Glucose – RDA 130g/day

• Muscles• Glucose• Glycogen• Fat

• Sources of carbohydrates (SMURF)• “Fattening” – mistaken thinking

ChemistChemist’’s View of s View of CarbohydratesCarbohydrates

• Carbohydrate family• Atoms and chemical bonds• Monosaccharides

• Chemical shorthand

• Glucose, fructose, galactose

• Disaccharides• Maltose, sucrose, lactose

• Polysaccharides

Atoms and Their BondsAtoms and Their Bonds


• Monosaccharides

• Chemical formula: C6H12O6

• Differing sweetness

• Fructose• Sweetest of the sugars

• Glucose – blood sugar• Part of every disaccharide

• Galactose• Only in a few foods

Chemical Structure of Glucose

The Monosaccharides

Descending order of sweetness


• Disaccharides• Pairs of three monosaccharides

• Sucrose – glucose and fructose

• Maltose – two glucose units

• Lactose – galactose and glucose

• Condensation• Links two monosaccharides together

• Hydrolysis• Breaks a disaccharide in two

Condensation and Hydrolysis Condensation and Hydrolysis of a Disaccharideof a Disaccharide


• Polysaccharides• Glycogen

• Storage form of energy in the body

• Glucose units

• Starch• Storage form of energy

in plants

• Glucose units

Starch (amylopectin) Starch (amylose)Glycogen

A glycogen molecule contains hundreds of glucose units in highly branched chains. Each new glycogen molecule needs a special protein (shown here in red) for the attachment of the first glucose.

A starch molecule contains hundreds of glucose molecules in either occasionally branched chains (amylopectin) or unbranched chains (amylose).

Stepped Art

Figure 4-6 p99


• Polysaccharides• Fibers

• Differ from starches: bonds cannot be broken down by human digestive system

• Soluble fibers – oats, barley, legumes, citrus• Lower cholesterol and blood sugar

• Insoluble fibers – bran, vegetables• Promote bowel health and movement



• Functional fibers• Naturally occurring, repurposed• Ex: Fiber One bars

• Resistant starches• Not digested or absorbed at all• Ex: just-ripe bananas, cooked potatoes, rice, pasta

• (Phytic acid)• (not a fiber, but found in fiber-rich foods, often)• (binds with minerals, blocks some absorption)



• (Phytic acid)• (not a fiber, but often found in fiber-rich foods)

• (binds with minerals, blocks some absorption)

The Bonds of Starch and Cellulose Compared

Carbohydrate DigestionCarbohydrate Digestion

• Goal of digestion: glucose for body to use• Breakdown, absorb (monosaccharides)

• Hydrolysis via enzymes• Mouth: short timespan

• Amylase (starch, maltose)

• Stomach: ceases• Stomach acid & protein-digesting enzymes• Fibers linger, delay gastric emptying

Carbohydrate DigestionCarbohydrate Digestion

• Small intestine: most of the work• Pancreatic amylase: polysaccharides• Specific disaccharide enzymes work

• Maltase• Sucrase

• Lactase • Large intestine: fibers remain

• Attract water• GI bacteria ferment water, gas, short-chain

fatty acids (i.e. some energy)

Carbohydrate AbsorptionCarbohydrate Absorption

• Remember: the goal is glucose!• Small % glucose absorbed through mouth• Active transport

• Glucose• Galactose

• Facilitated diffusion• Fructose

• Liver• Conversion of fructose and galactose

Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi.

In the liver, galactose and fructose share metabolic pathways with glucose.

Small intestine

Monosaccharides travel to the liver via the portal vein.

Stepped Art

Figure 4-9 p103

Glucose is used by most cell sin the body.

Lactose IntoleranceLactose Intolerance

• Lactase activity• Highest immediately after birth• Declines with age

• Symptoms of intolerance• Bloating, discomfort, diarrhea, gas

• Secondary intolerance: damaged intestinal villi (disease, meds, malnutrition)

• Prevalence• Genetically determined

Lactose IntoleranceLactose Intolerance

• Dietary changes• Manage, not eliminate

• <6g lactose (1/2 cup milk): asymptomatic

• Fermented milk products

• GI bacteria• Individualized diets• Potential nutrient deficiencies:

• Riboflavin, vitamin D, and calcium

Lactose in Selected Foods

Carbohydrate MetabolismCarbohydrate Metabolism

• Glucose is key player• Storing glucose as glycogen

• Liver storage• Condensation into glycogen

• Hydrolysis for release of glucose when needed

• Muscle storage• Selfishly hoards glycogen


• Glucose for energy• Fuels most of body’s cells

• Preferred source for brain, nerve cells, and developing red blood cells

• Cellular breakdown of glucose CO2 + H2O

• Making glucose from protein• Amino acid conversion• Gluconeogenesis


• Ketone bodies from fat fragments• Inadequate supply of carbohydrates

• Fat metabolism shifts

• Ketone body formation – starvation

• Ketosis – acid-base balance

• Carbohydrate needs for protein sparing and prevention of ketosis

• Using glucose to make fat

The Constancy of Blood The Constancy of Blood GlucoseGlucose

• Steady supply in blood stream• Intestines – food• Liver – glycogen

• Blood glucose homeostasis• Insulin

• Glucose from blood into cells

• Glucagon & epinephrine • Brings glucose out from storage

Maintaining Blood Glucose Maintaining Blood Glucose HomeostasisHomeostasis


• Balancing within the normal range• Balanced meals at regular intervals

• Diabetes• Insulin is either inadequate or ineffective• Type 1 diabetes• Type 2 diabetes

• Hypoglycemia• Prevalence


• Glycemic response• Speed of glucose absorption, level of blood

glucose, and return to normal glucose levels• Low glycemic response

• Desired

• High glycemic response• Glycemic index

• Benefits

• Utility

Health Effects of SugarsHealth Effects of Sugars

• Pleasure in moderate amounts• Obesity and chronic disease

• HFCS: glucose and fructose• Normally about 50/50 (like sucrose)

• Association between overweight and sweet desserts and soft drinks

• Added sugars (fructose, esp) favor fat-making pathways, impair fat-clearing pathways poor lipid panel


• Nutrient deficiencies• Energy with few other nutrients• Discretionary kcalories• Honey = Agave = Maple Syrup = Sugar

• Any health benefits are minor

• Choose nutrient dense first


• Dental caries• Bacteria ferment sugars producing acid• Food factors associated with tooth decay

• Time of food in mouth

• Sticky foods

• Frequency of sugar consumption

• Food choices• Factors associated with tooth decay

Enamel

Caries

Gum

Pulp (blood vessels, nerves)

Bone

Root canal

Nerve

Blood vessel

Crown

Stepped Art

Dentin

Figure 4-11 p111

Recommended Intakes of Recommended Intakes of SugarsSugars

• Dietary Guidelines• Reduce the intake of kcalories from added

sugars

• DRI• Added sugars: <25% of kcal• Impact on other food groups

• WHO and FAO recommendations• <10% of kcal

Alternative SweetenersAlternative Sweeteners

• Artificial sweeteners• Non-nutritive sweeteners• Large doses and adverse effects

• Stevia – an herbal product• Generally recognized as safe (GRAS)

• Sugar alcohols• Provide kcalories• Benefits and side effects

Health Effects of Starch and Health Effects of Starch and FibersFibers

• Heart disease• Soluble fibers: oat bran, barley, legumes• How?

• Soluble fiber binds with bile acids excretion liver must use own cholesterol

• Fiber fermentation in colon liver stops making cholesterol

• Improving heart disease risk factors


• Diabetes• Increase transit time, slows glucose

absorption, more stable blood sugars

• GI health• Incr stool weight, ease passage, reduce

transit time• Ample fluids• Stimulates muscles – retain strength


• Cancer• Dietary fiber and colon cancer

• Food, not supplements

• Sources of dietary fiber• Phytochemicals

• Preventing colon cancer• Diluting, binding, and removing

• Bacterial fermentation


• Weight management• High-fiber foods and whole grains

• Feeling of fullness

• Bulk to diet, nutritious, economical


• Excessive fiber• Insufficient energy or nutrient needs• Abdominal discomfort, gas, diarrhea• GI obstruction (too much, too soon)• Nutrient absorption• Dietary goals

• Balance, moderation, variety

Characteristics, Sources, & Characteristics, Sources, & Health Effects of FibersHealth Effects of Fibers

Recommended Intakes of Recommended Intakes of Starch & FibersStarch & Fibers

• DRI for carbohydrates• 45 to 65% of energy requirement

• RDA for carbohydrates• 130 grams per day

• Fiber• DRI: 14 grams per 1000-kcalories (no UL)

Fiber in Selected Foods

Fibers in Selected Foods

From Guidelines to GroceriesFrom Guidelines to Groceries

From Guidelines to GroceriesFrom Guidelines to Groceries

• Read food labels• Total carbohydrate

• Starch, fibers, sugars

• Sugars• Added and natural sugars

Bread Labels Compared

Carbs, kCalories, Carbs, kCalories, and and

ControversiesControversies

Highlight 4:Highlight 4:

Bonus Learning!Bonus Learning!

CarbohydratesCarbohydrates’’ kCalorie kCalorie ContributionsContributions

• Obesity and the link to carbohydrates• Total daily energy intakes have increased• Activity levels have declined• Increase in body weight

• Epidemiological studies• Inverse relationship between carbs & weight

• Weight loss• kCalorie intake

Energy Nutrients over Time

Daily Energy Intake & Increases in Adult Body Weight over Time

SugarsSugars’’ Share in the Problem Share in the Problem

• Increase in consumption of added sugars• High-fructose corn syrup• Body fat stores

• Carbohydrate cravings• Self-imposed labeling of foods

• Carbohydrate addictions• Not physiological or pharmacological

SugarsSugars’’ Share in the Problem Share in the Problem

• Appetite control• Fructose and insulin

• Flaws in plausibility

• Food form – liquid or solid• Simple to swallow

• Energy regulation

InsulinInsulin’’s Responses Response

• Surge of insulin levels• Glycemic effect

• Factors impacting glycemic effect• Glycemic index and body weight

• Insulin resistance• Fructose

• Prediabetes and metabolic syndrome

• Body’s insulin response

the carbohydrates: sugars, starches, and fibers

Documents

major uses of glucose

monosaccharidessucrose

hundreds of glucose

hundreds of glucose

digestion of carbohydrates

glucose unitslactose

health benefits

major sources of added