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Carbohydrates
Carbohydrates
• One of the three macronutrients
• A primary energy source, especially for
neurons (nerve cells)
• CH2O
• Grains, fruits and vegetables
Question
• Name ONE other macronutrient & tell
me its energy content (kcal/gram)
Where do Carbs originate?
• As glucose in plants!
• Glucose
– Most abundant
carbohydrate
– Produced by plants (&
other photosynthetic
organisms) via
photosynthesis
• Simple or complex
Data
•This is the general equation for photosynthesis—the
process of capturing sunlight energy and converting it
to chemical energy. Which of the following are the
reactants of this reaction?
–
–
C6H12O6 and O2.
CO2 and H2O.
Types of Carbohydrates
• Simple contain 1 or 2 monomers
– Monosaccharides contain 1
– Disaccharides contain 2
• Complex contain 100’s to 1000’s of
monomers
– Starches, glycogen, fibers
Monosaccharides: 1 monomer
• Glucose: usually occurs with other sugars
• Fructose: fruit & vegetable sugar
• Galactose: Always occurs with glucose in
foods
Disaccharides: 2 monomers
• Lactose: Milk sugar (glucose + galactose)
• Maltose: Malt sugar (glucose + glucose); by-product of
digestion & fermentation in our bodies; substrate for
fermentation in beer and liquor)
• Sucrose: Naturally occurring fruit sugar
Complex: 1000’s of monomers
• Starch: Storage form of glucose in plants
• Glycogen: Storage form of glucose in animals
– Muscle and liver
• Fiber: Form structural support elements of plants
What happens to Complex
Carbohydrates?
•
Starch
1. Digest starch to glucose
2. Convert it to usable energy, OR
3. store it as glycogen
Complex Carbohydrates
• Glycogen
– Not a source of dietary carbohydrate
– Convert excess glucose to glycogen store
it in liver & muscle cells
Complex Carbohydrates
• Fiber
– Dietary fiber: the non-digestible part of
plants
• Whole Grains, rice, seeds, legumes, fruits
contain dietary fiber
– Functional fiber is carbohydrate extracted
from plants and added to food
• Cellulose, guar gum, pectin, psyllium
– Total fiber = dietary + functional fiber
Digestion of Carbs
• Begins in the mouth
– Salivary amylase hydrolyzes starch to short
polysaccharides & maltose
– What kind of macromolecule is amylase?
– Mechanical digestion with teeth
• Stops in stomach
– HCl denatures amylase
• Resumes in SI
– Pancreatic amylase also digests carbs to maltose
Question
•
a)
b)
c)
d)
e)
Name another digestive organ that directly
adds secretions to the small intestine.
Stomach
Gall Bladder
Liver
a and b
b and c
Monosaccharide enter capillaries within
the intestinal villi.
In the liver,
galactose &
fructose are
converted to
glucose.
SI
Monosaccharides
travel to the liver via
the bloodstream.
Fig. 4-11, p. 110
Transport & Use
• ALL monosaccharides are converted to glucose
by the liver
– Q: Name one other monosaccharide.
• Glucose is our primary energy source
• Excess glucose is converted to glycogen by the
liver and stored in liver and skeletal muscles
– Q: Is this an anabolic or catabolic process
• Extreme excess glucose is converted to fatty
acids in the liver, and to glycerol in adipocytes
Storage of Glycogen
Digestion of Carbohydrates
• We do not have the enzymes necessary to
digest fiber
• Bacteria in large intestine can break down
some fiber
– Produce fatty acids and gas
• Most fiber remains undigested and is
eliminated with feces
Question
•
a)
b)
c)
d)
Where does digestion of
Carbohydrates NOT occur?
Mouth
Stomach
Small intestine
Large intestine
Regulation of Blood Glucose
• Amount of glucose (and therefore, access
to quick energy) in the blood
• Pancreatic cells produce, store and
secrete two hormones, insulin and
glucagon, which control level of glucose in
the blood
Regulation of Blood Glucose:
Insulin
• After eating, pancreas releases:
• Insulin
– Stimulates cells of the body to absorb
glucose from the bloodstream
– Stimulates the liver to absorb glucose and
convert it to glycogen
Regulation of Blood Glucose:
Insulin
Regulation of Blood Glucose:
Glucagon
• Glucagon
– Stimulates the breakdown (hydrolysis) of
glycogen to glucose to make quick energy
available to cells of the body
– Stimulates gluconeogenesis – production of
glucose from amino acids (AA)
• Where do these AA come from?
Regulation of Blood Glucose:
Glucagon
What about fructose?
Food & Blood Glucose
• Glycemic index: A food’s ability to raise
blood glucose levels
– Foods with a low glycemic index:
• Don’t produce dramatic fluctuations in blood
glucose
• May increase HDL/LDL ratio (good cholesterol)
• Are generally higher in fiber
• May reduce the risk of heart disease and colon
cancer
Glycemic indices
The Role of Carbohydrates
• Energy
– 4 kcal/kg
– Red blood cells rely only on glucose for
energy supply
– Glucose is especially important for energy
during exercise
The Role of Carbohydrates
• Energy source
• Fiber source
The Role of Carbohydrates
The Role of Carbohydrates
• Energy
– When we lack sufficient energy in the form
of carbs, we produce ketones (from fats &
Amino acids as an alternate energy source
• Are ketones harmful?
• Excessive ketones increase blood acidity
• High blood acidity damages body tissues, prevents
enzymes from functioning, etc.
– A byproduct of glucose metabolism (lactate)
is the ONLY fuel that some brain cells can
use.
The Role of Carbohydrates
• Energy
– Insufficient carbohydrate intake forces
the body to use alternate sources of
glucose
– Proteins are used for gluconeogenesis – the
production of new glucose
Role of Carbohydrates
Fiber
• May reduce risks of colon cancer & heart
disease
– By delaying absorption of dietary cholesterol &
replacing simple sugars
• **May enhance weight loss
– Occupies space so you feel full; also absorbs water
and expands
• **Associated with low rates of GI
diseases/disorders (hemorrhoids, constipation,
diverticulosis)
How Much Carbohydrate?
• Recommended Dietary Allowance (RDA)
is 130 grams/day just to supply the
brain with glucose
• **45-65% of daily calorie intake should
be in the form of carbohydrates
Type of carb matters
• Most Americans eat too many simple
sugars
– Most of these come from added sugars
– Added sugars = sugars and syrups added to
food during processing
• Common source is soda pop (~ 10 tsp. sugar per
12 oz. can)
• Average American consumes 40 gallons of soda
each year!
Simple vs. Complex Carbs
•Diets high in simple sugars:
– Contribute to dental problems such as cavities
and gum disease
• Cavity causing bacteria thrive on simple sugars
– Promote increased levels of ―bad cholesterol‖
and decreased levels of ―good cholesterol‖
• These changes are known to associate strongly with
heart disease
– Promote insulin insensitivity and diabetes
– Promote excess fat storage and obesity
Simple vs. Complex Carbs
• Complex carbs come associated with fiber
– Adequate Intake (AI) of fiber = 14 grams for every
1,000 kcal in the diet
– Most Americans eat only 1/2 the recommended
amount of fiber
• Whole grain foods come stocked with lots of
fiber and vitamins & minerals without any added
sugar
Alternatives to sugar
• Nutritive sweeteners
– Contain 4 kcal energy per gram
– Sucrose, fructose, honey, brown sugar, sugar
alcohols
• Non-nutritive (alternative) sweeteners
– Provide little or no energy
Alternative Sweeteners
•Acceptable Daily Intakes (ADI) have been
established for:
–Aspartame (Equal; Nutrasweet)
–Sucralose (Splenda)
–acesulfame-K (Sweet One)
•No ADI has been set for saccharin but it
has been removed from the list of cancercausing agents.
Alternative Sweeteners
Health Disorders
Three health disorders related to
carbohydrate metabolism
1. Diabetes
2. Gluten Sensitivity; Coeliac Disease; Wheat
Allergy
3. Hypoglycemia
4. Lactose intolerance
Diabetes
Inability to regulate blood glucose levels
• Three types:
– Type 1 diabetes
– Type 2 diabetes
– Gestational diabetes
• Untreated diabetes can cause nerve
damage, kidney damage, blindness, and
death
Diabetes
• Type 1 diabetes
Type 2
Type 1
10%
90%
– Accounts for 10% of all cases
– Patients do not produce enough insulin
– Causes hyperglycemia – high blood sugar
(glucose)
– Requires insulin injections
– Autoimmune disease?
Type 2
Diabetes
• Type 2 diabetes
Type 1
10%
90%
– Most diabetics have Type 2 diabetes
– Body cells have grown insensitive or
unresponsive to insulin
– Excess insulin is produced by pancreas,
until those cells ―wear out‖
– Causes hyperglycemia because body cells
cannot absorb glucose from the blood
Diabetes
• Type 2 diabetes
– Causes include genetic predisposition,
obesity, and physical inactivity
– Treated with diet, exercise, and possibly
oral medications
– Healthy lifestyle choices may prevent or
delay onset of type 2 diabetes
Gluten Sensitivity
• A spectrum of immune responses
(differing in severity) to a range of
proteins found in wheat
– IgA mediated response (local inflammation &
accumulation of WBC
– Stimulated by various wheat proteins
(prolamins and glutelins)
– Typically applied to patients presenting with
dermatitis herpetiformis
Coeliac Disease
• Mechanism
– IgA responds to prolamin
– Villi flatten, WBC infiltrate and
destroy cells
– Damage prevents absorption of all
nutrients
• Incidence
– 0.6 – 1%: general population
– 2.6%: 2 relatives of patients
– 4.5%: 1 relatives of patients
• All Tritaceae possess these
allergens:
– Wheat, Rye, Barley
Normal vs. Coeliac SI
• Reduced villi
• Increase
crypt size
• Higher
density of
WBC
Wheat Allergy
• Mechanism
– IgE antibodies AND Mast cells respond to
gluten proteins
– Causes systemic inflammation and disturbance
of muscle tone: constriction, dilation, spasms
• Smooth muscle constriction – closes airway
• muscle spasms – bladder control, coronary
• Smooth muscle relaxation - vasodilation and BP
drop
• Incidence??? – less than 0.5%
Hypoglycemia
• Hypoglycemia
– Low blood sugar (glucose)
– Reactive hypoglycemia results when too much
insulin is produced after a meal
• Causes shakiness, sweating, anxiety
– Fasting hypoglycemia results when too much
insulin is produced even when the patient has
not eaten
Lactose Intolerance
• Lactose intolerance
– Insufficient lactase production = inability to
digest lactose (milk sugar)
– Symptoms = intestinal gas, bloating, nausea,
cramping, diarrhea
– Alternate sources of calcium
• Tomato juice, seaweed, cabbage, squashes, beets