chapter 4: carbohydrates plants synthesize glucose

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