chapter 4: carbohydrates plants synthesize glucose
Post on 21-Dec-2015
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Chapter 4: Carbohydrates
Plants Synthesize Glucose
Monosaccharides
Structure
GlucoseFructose
Galactose
Fructose (fruit sugar)
Metabolized to glucose in the liver
Found in fruit, honey, and high fructose corn syrup
Is in sucrose
Galactose
Usually bound with glucose (lactose)
Converted to glucose in the liver
Available fuel source
Disaccharides
“Simple sugars”
Maltose (Gluc + Gluc)
Fermentation
Alcohol production
Sucrose (Gluc + Fruc)
Sugar
Lactose (Galactose + Gluc)
Milk products
Complex Carbohydrates
Polysaccharides: Starch & Glycogen
Amylose
Amylopectin
Dietary fiber
Oligosaccharides
3-10 monosaccharides
Found in beans and legumes
Not digested
Metabolized by bacteria in the large intestine
Beno®
Polysaccharides: Starch
3,000 or more monosaccharides bound together
Starch
Amylose--straight chain polymer
Amylopectin--highly branched polymer
Glycogen
Storage form of CHO for animals and human
Structure similar to amylopectin
More sites for enzyme action
Found in the liver and muscles
Dietary Fiber
Undigested plant food
Body cannot break the bonds
Insoluble fiber
Cellulos, hemicellulose, lignin
Not fermented by the bacteria in the colon
Soluble fiber
Gum, Pectin, Mucilage
Fruit, vegetable, rice bran, psyllium seed
Soluble and Insoluble Fiber
Health Benefits of Dietary Fiber
Absorbs and holds water
Soften stool
Larger stool promotes peristalsis
Promotes regularity
Lower risk for cardiovascular disease
Decrease hemorrhoids and diverticula
Diverticula
CHO in Food
Sweeteners
Sucrose--benchmark of all sweeteners
Same caloric content (4 kcals/gm)
No health benefit over another
Consumption ranges: 14-48 lbs/yr per person
Types of Sweeteners
High-fructose corn syrupcornstarch treated with acid and enzymesconversion of glucose into fructosesame degree of sweetness as sucrosecheaper and used in many food products
Brown sugarMaple syrupHoneySugar alcohols
1.5-3 kcal/gAbsorbed and metabolized slowerLarge amount causes diarrhea
Sugar Substitutes
Saccharin
First produced in 1879
180-200x sweeter than sucrose
Excessive intake is linked to bladder cancer in lab animals
Not a potential risk in humans
Aspartame (NutraSweet)
Composed of phenylalanine, aspartic acid, and methanol
180-200x sweeter than sucrose4 kcal/gm, but only a trace amount is needed to
sweeten foodsNot heat stableComplaints of sensitivity to aspartame
headaches, dizziness, seizures, nausea, etc.
Not recommended for people with phenylketonuria (PKU)
Acesulfame-K (Sunette)
Newest sugar substitute
200x sweeter than sucrose
Not digested by the body
Heat stable
Diabetisweet used in baking
Sucralose (Splenda)
600x sweeter than sucrose
Substitute chlorines for hydroxyl groups on sucrose
Heat stable
Tiny amount digested
Digestion
Effects of Cooking
Softens fibrous tissues
Easier to chew and swallow
Digestion of Carbohydrate in the Mouth
Saliva contains amylase
Starch is broken down to shorter saccharides
Taste the sweetness with prolong chewing
Proceeds down the esophagus
Digestion of Carbohydrate in the Stomach
The acidic environment stops the action of salivary amylase
No further starch digestion occurs
In the Small Intestine
Pancreatic amylase is releasedIntestinal cells release enzymes Maltose + maltase glucose + glucose Sucrose + sucrase glucose + fructose Lactose + lactase glucose + galactose
Monosaccharides are absorbed
CHO Digestion
CHO Absorption
Glucose and GalactoseActive absorption
Energy is expended
Going from low to high concentration gradient
Fructose
Facilitated diffusion using a carrier
No energy expended
Portal Vein
Transport absorbed monosaccarhides
Delivers them to the liver
Liver can:
transform them into glucose
release them back into the blood stream
store as gylcogen (or fat)
Functions of Carbohydrate
Supplies energy
Protein sparing
Prevent ketosis
Sweetener
Regulation of Blood Glucose
Hyperglycemia
Hypoglycemia
Blood Glucose Control
Role of the liver
Regulates glucose that enters bloodstreamRole of the pancreas
Release of insulin
Release of glucagon
Functions of Insulin
Promotes glycogen synthesis
Increases glucose uptake by the cells
Reduces gluconeogenesis
Net effect: lowers the blood glucose
Functions of Glucagon
Breakdown glycogen
Enhances gluconeogenesis
Net effect: raises blood glucose
Epinephrine/ Norepinephrine
“fight or flight” response
breakdown glycogen
raises blood glucose
Diabetes Mellitus-Type 1
Genetic link
Decreased release of insulin
Insulin dependent
Hyperglycemia
Immunological disorder
Early introduction of cow’s milk
Treatment for Type 1
CHO counting
Insulin therapy
Risk for heart disease
Diabetes Mellitus-Type 2
Genetic linkAssociated with obesityNon-insulin dependent to startAccounts for majority of cases of DMDefective insulin receptors on the cellsOver secretion of insulin to compensateLeads to beta cells failureTreatment: medication and diet therapy (weight
loss)
Consequences of Uncontrolled Blood Glucose
Ketosis leading to ion imbalances, dehydration, coma, death
Degenerative diseases
Nerve damage, Heart disease, Kidney disease, Blindness
Atherosclerosis
Increase risk for wound infections
Hypoglycemia
Reactive hypoglycemia
Occurs 2-4 hours after eating a meal
Possibly due to over secretion of insulinFasting hypoglycemia
Usually caused by pancreatic cancer
Leads to overproduction of insulin
Sweetener Function
Enhances flavor
Use in moderation
Recommended Intake
No RDA (yet)
Consume at least 50 gm to prevent ketosis
National Cholesterol Education Program recommends 50-60% of kcal from CHO
Current intake is ~50%
Health Benefits of Dietary Fiber--Recall
Promotes softer, larger stool and regularity
Slows glucose absorption
Reduces blood cholesterol
Reduces heart disease
Reduces hemorrhoids and diverticula
Recommended Dietary Fiber Intake
20-35 gm of fiber/day (10-13 gm/1000 kcals)
Children: age +5gm/day
Ave. U.S. intake: ~16 gm/day
Too much fiber (>60 gm/d) will:require extra intake of fluid
bind to some minerals
develop phytobezoars
fills the stomach of a young child quickly
Recommendation for Simple Sugar Intake
Low nutrient density
Recommends no more than 10% of total kcal/day
Ave. U.S. intake: 16% of total kcal/day
Added to food and beverages during processing
High Sugar Diets
Empty calories
Soda replacing milk
Calories adding to excess
Dental caries
exposure to teeth
High glycemic index
Blood glucose response of a given food
Influence by various factors
Effects of High Glycemic Index CHO
Stimulates the release of insulin
Insulin’s effect blood triglycerides level
Insulin’s effect LDL
Insulin increases fat synthesis
Return to hunger quicker
Develop insulin resistance
Lactose Intolerance
Reduction in lactase
Lactose is undigested and not absorbed
Lactose is metabolized by large intestinal bacteria
causes gas, bloating, cramping, discomfort
Primary lactose intolerance disease
Secondary lactose intolerance disease
What To Do If You Are Lactose Intolerance
Determine amount you can tolerate
Eat dairy with fat
Cheese & yogurt are usually tolerated well
Use of Lact-Aide