Transcript simple carbohydrates

DNT 200
NUTRITION FOR HEALTH
SCIENCES
CARBOHYDRATE
1
CARBOHYDRATE
Things sweet to taste prove in digestion sour.
Shakespeare, King Richard II
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CARBOHYDRATE
DEFINITION
Carbohydrates are
compounds composed
of carbon, hydrogen
and oxygen arranged
as monosaccharides or
multiples of
monosaccharides
(disaccharides &
polysaccharides)
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CARBOHYDRATE
4
CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Monosaccharides
(single sugars)
Glucose
– Also known as
• Blood sugar
• Grape sugar
• Dextrose
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Monosaccharides (single
sugars)
Glucose (continued)
Plants capture the sun’s
radiant energy and through
photosynthesis, trap this
energy in glucose
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CARBOHYDRATE
SIMPLE CARBOHYDRATES
Monosaccharides (single sugars)
Glucose (continued)
– Is common to all disaccharides and
polysaccharides
– Is the chief fuel of the body’s cells
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Monosaccharides (single
sugars)
Fructose
– Also known as levulose
– Is the sweetest of sugars
– The body can convert
fructose to glucose or can
break it into fragments from
which fat can be made
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CARBOHYDRATE
SIMPLE CARBOHYDRATES
Fructose
• Endocrine and metabolic effects include an
increased risk for insulin resistance and
hyperinsulinemia
• Common sources
– Sucrose
– High fructose corn syrup
• Cheaper than sucrose
• Represents the biggest change in our diets in the last 15
years
• Used in sodas, juice boxes, bread, and a host of other
foods
– Natural sweeteners high in fructose (e.g. honey) are not
associated with the above cited negative changes
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Monosaccharides (single
sugars)
Galactose
– Does not appear singly in
nature
– Found only as a part of
lactose
– During digestion, galactose
is freed as a single sugar
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CARBOHYDRATE
SIMPLE CARBOHYDRATES
Disaccharides (double sugars)
• Are pairs of single sugars linked together
• A condensation reaction is one where two
reactants combine to yield a larger product such as
when two monosaccharides link together to form a
disaccharide and a molecule of water is created
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CARBOHYDRATE
SIMPLE CARBOHYDRATES
Disaccharides (double sugars)
• A hydrolysis reaction is one where a major
reactant is split into two products such as when a
disaccharide is cut in two with a molecule of water
forming two monosaccharides
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Disaccharides (double
sugars)
Maltose
– Consists of two glucose
units
– Is a plant sugar -- is a minor
constituent in a few foods to
include malt and
germinating cereals
– Also known as malt sugar
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Disaccharides (double sugars)
Sucrose
– Most familiar of the three
disaccharides
– Consists of one glucose unit
and one fructose unit
– Also known as table or white
sugar
– Is usually obtained by refining
the juice from sugar beets or
sugar cane to provide the
brown, white, and powdered
sugars
– Also occurs naturally in many
fruits and vegetables
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Disaccharides (double
sugars)
Lactose
– Consists of glucose
and galactose
– Is the principle
carbohydrate of milk
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CARBOHYDRATE
SIMPLE
CARBOHYDRATES
Disaccharides (double sugars)
Lactose
Lactose intolerance is the
condition that results from an
inability to digest the milk sugar
lactose. It is characterized by
bloating, gas, abdominal
discomfort and diarrhea
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CARBOHYDRATE
COMPLEX
CARBOHYDRATES
Energy Yielding
Polysaccharides
Starch
– Is the main storage material
of plants
– Is composed of hundreds of
glucose units linked
together
– When you eat a plant, your
body splits the starch into
glucose and uses the
glucose for energy
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
Energy Yielding Polysaccharides
Starch (continued)
Food Sources of Starch
– Grains (wheat, rice, corn, etc.)
– Legumes (peanuts, dry beans, dry peas)
– Root Vegetables (potatoes, yams)
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
Energy Yielding Polysaccharides
Glycogen
– Is the storage form of glucose
– Also composed of glucose units -- more complex
than starch and highly branched
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
Energy Yielding Polysaccharides
Glycogen
– Not important as a food source of carbohydrate
– Found in meats only to a limited extent -- does not
occur in plants
– Made and stored by the liver and muscle tissues
– Is the form in which the human body stores much of
its glucose
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
Non-Energy Yielding Polysaccharides
Fibers
– Are the structural parts of plants
– Are non-starch polysaccharides (and some nonpolysaccharides)
– Not digested by human digestive enzymes (some are
digested by GI tract bacteria)
– Can be classified as soluble or insoluble, depending
on their solubility in water
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CARBOHYDRATE
COMPLEX CARBOHYDRATE
Non-Energy Yielding Polysaccharides
Type of Fiber
Major Food
Sources
Action in the Body
Soluble Fibers
Gums, pectins,
some
hemicelluloses,
mucilages
Insoluble Fibers
Cellulose, many
hemicelluloses,
lignins
Fruits (apples,
citrus), oats, barley,
legumes
Delay GI transit (benefits
digestive disorders)
Delay glucose absorption
(benefits diabetes)
Lower blood cholesterol
(benefits heart disease)
Wheat bran, corn
bran, whole-grain
breads and cereals,
vegetables (such as
cabbage, carrots, and
brussels sprouts)
Accelerate GI transit
Increase fecal weight
(promotes bowel
movements)
Slow starch hydrolysis
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Delay glucose absorption
CARBOHYDRATE
COMPLEX CARBOHYDRATES
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
Non-Energy Yielding Polysaccharides
Fiber Terminology
– Dietary Fiber -- Edible, non-digestible components
of carbohydrates and lignin naturally found in plant
food. Examples include cereal bran, flaked corn
cereal, sweet potatoes, legumes
– Functional Fiber -- Fiber sources shown to have
similar health benefits as dietary fiber, but are
synthetic. Examples include pectin extracted from
citrus peel and used as a food ingredient
– Total Fiber -- Dietary fiber + Functional fiber
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CARBOHYDRATE
COMPLEX CARBOHYDRATES
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CARBOHYDRATE
CARBOHYDRATE METABOLISM
Stored Glucose
• Glycogen stored and released by the liver -- only a
few hours worth is stored)
• Falling blood glucose signals that body cells need
glucose -- liver cells dismantle glycogen into
single molecules of glucose, which is released into
the bloodstream
• Muscle cells can also store glycogen (about 2/3 of
the body’s supply) but it is used by these cells for
start-up and intensive exercise
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CARBOHYDRATE
CARBOHYDRATE METABOLISM
Using Glucose for Energy
• When glucose enters a cell, enzymes break it in
half
– The halves can be put back together again to make
glucose OR
– Can be broken down into smaller fragments
• Fragments
– Can yield energy when broken down completely
into CO2 and water OR
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– Can be reassembled into units of body fat
CARBOHYDRATE
CARBOHYDRATE METABOLISM
Making Glucose From Protein
Gluconeogenisis -- is when glucose is made from
a non-carbohydrate source
• Making glucose from protein
– Body protein can be converted to glucose
(gluconeogenisis)
• Body fat cannot be converted to glucose to any
significant extent, although fat breakdown can
yield energy for many of the body’s cells
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CARBOHYDRATE
CARBOHYDRATE METABOLISM
Making Glucose From Protein
• Only glucose can provide energy for:
– Brain cells
– Other nerve cells
– Developing red blood cells
• Only adequate dietary carbohydrate can prevent
the use of protein for energy -- this role of
carbohydrate is known as its protein sparing action
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CARBOHYDRATE
CARBOHYDRATE METABOLISM
Making Ketone Bodies From Fat Fragments
Ketone Bodies -- the product of incomplete breakdown of fat
when glucose is not available in the cells
• Inadequate carbohydrate may result in more fat being broken
down -- but not all the way to energy
• Fat fragments combine with each other, forming ketone
bodies
– Muscles and other tissues can use ketone bodies for
energy
– When production of ketone bodies exceeds their use, they
accumulate in the blood causing ketosis, which disturbs
the body’s normal acid-base balance
• 50-100 grams of carbohydrate per day spares protein and
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prevents ketosis
CARBOHYDRATE
CARBOHYDRATE METABOLISM
Converting Glucose to Fat
• Given more carbohydrate than it needs the body
– Uses glucose for energy needs
– Fills glycogen stores to capacity
• Leftover is broken down by the liver (along with
protein and fat fragments) into smaller molecules
– Are then re-assembled as fat and stored
– A minor pathway compared to the conversion of dietary
fat to body fat
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Homeostasis -- the maintenance constant internal
conditions by the body’s control systems
• Glucose must be maintained within limits that
allow cells to nourish themselves
– Too low and you become dizzy and weak
– Too high and you become confused and have difficulty
breathing
– Extremes left untreated can result in death
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Blood Glucose Regulators
– Insulin -- a hormone secreted by the pancreas in
response to (among other things) increased blood
concentration
• Circulating insulin contacts the receptors in the body’s
cells -- receptors respond by ushering glucose from the
blood into the cells
• Most of the cells take only the glucose they can use for
energy right away
• The liver and muscle cells can assemble the small glucose
units into long branching chains of glycogen for storage
• The liver can also convert glucose to fat for export to
other cells
• Thus, high blood glucose returns to normal as excess
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glucose is stored as glycogen and fat
CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Blood Glucose Regulators (continued)
Glucagon -- a hormone secreted by the pancreas in
response to low blood glucose concentrations
that elicits the release of glucose from storage
• Glucagon signals the liver to dismantle its
glycogen stores and release glucose into the blood
for use by all the other body cells
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Blood Glucose Regulators (continued)
– Epinephrine -- a hormone secreted by the adrenal
gland that modulates the stress response
• Formerly called adrenaline
• Acts quickly when a person experiences stress,
ensuring that all the body cells have energy fuel
in emergencies
• Like glucagon, epinephrine works to return
glucose to the blood from liver glycogen
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Balancing within the Normal Range
– When blood glucose falls too low
• Replenished by food
• In the absence of food, glucagon can signal the liver
to break down glycogen stores
– When blood glucose rises too high
• Insulin can signal the cells to take in more glucose
for energy
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Balancing within the Normal Range
– Eating balanced meals (abundant complex
carbohydrates - including fiber, some protein, and a
little fat) helps the body maintain a happy medium
between the two extremes
• Fibers and fat slow down the digestion and absorption of
carbohydrate enabling glucose to enter the blood
gradually
• Dietary protein elicits the secretion of glucagon, whose
effects oppose those of insulin
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CARBOHYDRATE
BLOOD GLUCOSE
Glucose Regulation
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CARBOHYDRATE
BLOOD GLUCOSE
Glucose Regulation
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CARBOHYDRATE
BLOOD GLUCOSE
Glucose Regulation
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CARBOHYDRATE
BLOOD GLUCOSE
Glucose Regulation
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Falling outside the Normal Range
In some people, blood glucose regulation fails
• Diabetes
– Insulin Dependent Diabetes Mellitus (IDDM) -- body
fails to produce insulin
» Less common
» Also known as Type I Diabetes or juvenile-onset
diabetes
– Non-Insulin Dependent Diabetes Mellitus
(NIDDM) -- cells fail to respond to insulin
» More common
» Also known as Type II Diabetes
» Is usually milder than IDDM and
progresses more slowly
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CARBOHYDRATE
BLOOD GLUCOSE
Maintaining Homeostasis
Falling outside the Normal Range (continued)
• Hypoglycemia -- an abnormally low blood glucose
concentration
– Failures in blood glucose regulation are due to
abnormalities in the body’s regulatory system,
which alter the way that it responds to foods
– That is, food does not govern the blood glucose
level -- the body does
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CARBOHYDRATE
GLYCEMIC EFFECT
• Is a measure of the extent to which a food, as
compared to pure glucose, raises the blood glucose
concentration and elicits an insulin response
• Refers to:
– How quickly glucose is absorbed after a person eats
– How high the blood glucose rises
– How quickly it returns to normal
• Different foods foods have different effects on
blood glucose
• Effect differs depending on whether the food is
eaten alone or as a part of a meal
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CARBOHYDRATE
GLYCEMIC INDEX OF SELECTED FOODS
Low (best)
Pumpernickel bread
Pasta
Bran cereals
Moderate (better)
Grains
Sourdough bread
Shredded Wheat
High (good)
White bread
Short-grain rice
Cornflakes
Waffles
Vegetables & Legumes
Soybeans
Lentils
Baked beans
Potatoes
Carrots
Fruits
Peaches
Banana
Apples (& apple juice) Pineapple
Oranges
Orange juice
Milk Products
Milk, Yogurt
Ice cream
Sweets
Chocolate
Watermelon
Jelly beans
Soft drinks
Honey
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CARBOHYDRATE
GLYCEMIC EFFECT
• Pros & Cons
– Lowering the glycemic index of of the diet reduces insulin
secretion and improves glucose and lipid metabolism
– May help prevent heart disease and diabetes
– May help prevent obesity
– Prolongs the presence of food in the digestive tract thus
providing greater satiety and diminishes the insulin
response
– Is complicated to teach
– Relatively few foods have had glycemic index determined
– Information is neither intuitively apparent nor printed on
food labels
– Concern that consumers will adopt a low carbohydrate diet
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instead of a low glycemic one
CARBOHYDRATE
Added Sugars in the US Diet
Others
5%
Other
beverages
4%
Cereals
4%
Milk Products
9%
Soft Drinks
33%
Fruit Drinks
10%
Sweetened
Grains
19%
Sugars &
Candy
16%
Soft Drinks
Sugars & Candy
Sweetened Grains
Fruit Drinks
Milk Products
Cereals
Other beverages
Others
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CARBOHYDRATE
HEALTH EFFECTS
Sugar
– In the amounts people currently
consume, sugar carries no
proven health risk (FDA and
National Academy of Sciences
Data)
– Obesity -- sugar can contribute
to obesity but does not, by itself
cause obesity
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CARBOHYDRATE
HEALTH EFFECTS
Sugar (continued)
– Diabetes
• Body fatness seems to be
more related to diabetes than
diet is
• Obesity is a major factor in
the causation of Type II
diabetes
• Sugar may be a causative
factor only if and when it
contributes to obesity
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CARBOHYDRATE
HEALTH EFFECTS
Sugar (continued)
– Heart Disease
• Fat, not sugar, is
clearly the major
dietary culprit
• Moderate sugar
intake does not
influence the risk of
heart disease
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CARBOHYDRATE
HEALTH EFFECTS
Sugar (continued)
– Hyperactive Behavior in
Children
• No sugar link confirmed by
scientific research
• Sugary foods may replace
nutrient-dense foods causing
nutrient deficiencies -- and
deficiencies can cause adverse
behavior
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CARBOHYDRATE
HEALTH EFFECTS
Sugar (continued)
– Dental Caries
• Evidence says there is a relationship -however ANY carbohydrate-containing food
can support bacterial growth
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CARBOHYDRATE
HEALTH EFFECTS
Sugar (continued)
– Dental Caries
• Bacterial growth produces acid that eats
away the enamel causing dental decay
• Level of dental caries seems to be more
related to the frequency of sucrose intake
than the quantity of sucrose ingested
• Retentive solid forms of sugar appear to be
more cariogenic than liquid forms of sugar
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CARBOHYDRATE
HEALTH EFFECTS
Complex Carbohydrates
– Because diets high in carbohydrates (and low in
concentrated sugar) are also usually low in fat and
energy and high in fiber, vitamins and minerals,
health benefits area realized in the reduced risk of:
•
•
•
•
•
•
Obesity
Cancer
Cardiovascular Disease
Diabetes
Dental Caries
Malnutrition
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CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Weight Control
• Fiber contributes little energy & promotes a
feeling of fullness as it absorbs water
• Diets high in fiber-rich foods can promote weight
loss if these foods displace concentrated fats and
sweets
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CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Constipation, Hemorrhoids
• Some fibers attract water into the
digestive tract thereby softening the stool
• Water-insoluble fibers (such as cellulose)
contribute undigested residue in the
digestive tract thereby enlarging the stool
• Large soft stools ease elimination for the
rectal muscles
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CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Appendicitis
• Prevents compaction of the intestinal
contents
• Compaction could allow the appendix to
become obstructed and permit bacteria to
invade and infect it
– Diverticulosis
• Stimulates the muscles of the digestive tract
• Muscles retain their strength and resist 57
bulging into pouches known as diverticula
CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Colon Cancer
• Populations consuming highfiber diets generally have
lower rates of colon cancer
• Fiber may prevent colon
cancer by diluting, binding,
and rapidly removing
carcinogens
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CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Heart Disease
• Some fibers bind with bile (the emulisifyer
that assists with cholesterol and fat
absorption)
• With less bile available, fat and cholesterol
absorption diminishes and blood lipid
concentrations decline
• Blood cholesterol levels decline further as the
liver makes more bile from cholesterol to
replace the bile bound to fiber and excreted
• Products of fiber digestion, once absorbed, 59
also inhibit cholesterol synthesis
CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Glycemic Response and
Diabetes Control
• Some fibers can trap
nutrients and delay their
leaving the stomach for the
small intestine
• Glucose absorption is
thereby slowed, eliciting a
moderate insulin response
and a moderate rise in
60
blood glucose
CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Negative Health Effects
• May displace energy- and nutrient-dense
foods
• When fiber intake is increased too rapidly,
intestinal discomfort and gas may be
experienced, therefore, increase gradually
and be sure fluid intake is adequate
61
CARBOHYDRATE
HEALTH EFFECTS
Fiber
– Not All Fibers Have Similar Effects
• Wheat bran (composed of mostly insoluble
cellulose) has no cholesterol lowering effect
while oat bran (soluble) pectin (soluble) do
• Wheat bran is an effective stool-softening
fiber
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CARBOHYDRATE
RECOMMENDED INTAKES
SUGARS AND STARCH
DIETARY REFERENCE INTAKE VALUE
• EAR
– 100 grams (for brain glucose utilization)
• RDA
– 130 grams (for brain glucose utilization)
• Distribution range for healthy diets
– 45% - 65% of total Calories
2002 Data
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CARBOHYDRATE
RECOMMENDED INTAKES
FIBER
DIETARY REFERENCE INTAKE VALUE
• AI
– Men under 50 -- 38 grams
– Men over 50 -- 30 grams
– Women under 50 -- 25 grams
– Women over 50 -- 21 grams
For greatest protection against coronary heart
disease
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2002 Data
CARBOHYDRATE
ALTERNATIVES TO SUGAR
ASPARTAME
• Sold as Nutrasweet
• L-alpha-aspartyl-L-phenylalanine methyl
ester
• Major consideration is in the use of
aspartame in children is in patients with
autosomal recessive phenylketonuria
• Seizures, headache, nervousness, dizziness,
memory impairment, nausea, temper
outbursts, and depression are potential side
effects but little controlled documentation
*****
exists
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CARBOHYDRATE
ALTERNATIVES TO
SUGAR
Saccharin
• O-toluene sulfonamide derivative
• High consumption in infants is
associated with irritability, excessive
tone of the skeletal muscles, insomnia,
spasms, and strabismus (a deviation of
the eye)
• No longer associated with cancer risk
in humans
****
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CARBOHYDRATE
ALTERNATIVES TO
SUGAR
Sucralose
• Sold as Splenda and marketed Fall
2000
• A chlorinated sucrose derivative
• Small risk for shrunken thymus glands
(up to 40% shrinkage) and enlarged
liver and kidneys
• Breaks down into small amounts of
1,6-dichlorofructose (a chemical
which has not been adequately tested
in humans and might pose cancer
or
***
neurological risk
67
CARBOHYDRATE
ALTERNATIVES TO
SUGAR
Stevioside
• Sold as Stevia
• Natural sweetener extracted from the
leaves of Stevia rebaudiana
• Little risk for mutagenicity or
carcinogenicity
• Suited for both diabetics, and PKU
patients, as well as obese persons
intending to loose weight by avoiding
sugar supplements in the diet
• No allergic reactions to it seem to
**
exist
68
CARBOHYDRATE
ALTERNATIVES TO
SUGAR
Sugar Alcohols
•
•
•
•
Natural sugars with Calories
Examples -- sorbitol, mannitol, xylitol
Slow absorption
60+ grams per day can be hazardous to
diabetics -- liver converts the excess to
simple sugar (a problem if not enough
insulin is produced)
• Even with no blood sugar abnormalities,
the increase in glucose can hormonally
alter insulin and glucagon levels to limit
fat release
*
69
CARBOHYDRATE
ALTERNATIVES TO
SUGAR
Tagatose
• D-Tagatose
• Is a levo-sugar (left-handed sugar)
• To the tongue, tastes just like regular
sugar
• Body cannot digest it
• Ingestion of large amounts may result in
GI distress including diarrhea, nausea,
and flatulence
• Marketed as Naturlose
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