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The Carbohydrates: Sugars, Starches, and Fibers. Chapter 4. Chapter 4 Objectives. Identify the monosaccharides, disaccharides, and polysaccharides common in nutrition by their chemical structures and major food sources. Classify carbohydrates as mono-, di-, or polysaccharides. - PowerPoint PPT Presentation
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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
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• 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
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• 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
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• 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
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• 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
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• Polysaccharides• Fibers
• 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)
ChemistChemist’’s View of s View of CarbohydratesCarbohydrates
• Polysaccharides• Fibers
• (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
Carbohydrate MetabolismCarbohydrate Metabolism
• 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
Carbohydrate MetabolismCarbohydrate Metabolism
• 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
The Constancy of Blood The Constancy of Blood GlucoseGlucose
• 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
The Constancy of Blood The Constancy of Blood GlucoseGlucose
• 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
Health Effects of SugarsHealth Effects of Sugars
• Nutrient deficiencies• Energy with few other nutrients• Discretionary kcalories• Honey = Agave = Maple Syrup = Sugar
• Any health benefits are minor
• Choose nutrient dense first
Health Effects of SugarsHealth Effects of Sugars
• 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
Health Effects of Starch and Health Effects of Starch and FibersFibers
• 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
Health Effects of Starch and Health Effects of Starch and FibersFibers
• Cancer• Dietary fiber and colon cancer
• Food, not supplements
• Sources of dietary fiber• Phytochemicals
• Preventing colon cancer• Diluting, binding, and removing
• Bacterial fermentation
Health Effects of Starch and Health Effects of Starch and FibersFibers
• Weight management• High-fiber foods and whole grains
• Feeling of fullness
• Bulk to diet, nutritious, economical
Health Effects of Starch and Health Effects of Starch and FibersFibers
• 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