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Chapter 2
Carbohydrates
Man shall not live by bread alone.
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1
Key Concepts
• Carbohydrate foods provide practical
energy (calorie) sources because of their
availability, relatively low cost, and
storage capability.
• Carbohydrate structures vary from simple
to complex to provide both quick and
extended energy for the body.
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2
Classes of Carbohydrates
• Monosaccharides
– Simple sugar
– Simple carbohydrate
• Glucose
• Fructose
• Galactose
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3
Classes of Carbohydrates,
cont’d
• Disaccharides
– Double sugar
– Simple carbohydrate
• Sucrose (glucose and fructose)
• Lactose (glucose and galactose)
• Maltose (glucose and glucose)
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4
Classes of Carbohydrates,
cont’d
• Polysaccharides
– Starch
– Glycogen
– Dietary fiber
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5
Starch
• Most significant
polysaccharide in the diet
• Whole grains retain the bran
layer, inner germ, and
endosperm, including the
nutrients naturally found in
the plant
• Enriched grains are refined
grains that have nutrients
added back to them
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6
Other Sweeteners
• Nutritive sweeteners
– Sugar alcohols (sorbitol, mannitol,
xylitol)
• Non-nutritive sweeteners
– Artificial sweeteners in food
(Examples in next slide)
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7
Sweetness of Sugars and
Artificial Sweeteners
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8
Focus on Dietary Fiber
• Cellulose
– Remains undigested in the
gastrointestinal tract and provides bulk
to a diet
– Bulk helps move the food mass through
the intestine (prevents constipaton)
– Examples:
• Stems, leaves of vegetables, corn hull,
beans, coverings of seeds and grains
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9
Focus on Dietary Fiber,
cont’d
• Noncellulose polysaccharides
– Absorb water and swell to a larger bulk
– Examples: pectins from fruit; gums &
mucilages – secretions from plants like
okra; algal substances - seaweed
• Lignin
– Only noncarbohydrate type of dietary
fiber
– Woody parts of plants (broccoli stems
& seeds)
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10
Focus on Dietary Fiber,
cont’d
• Divided into two groups based on solubility
– Insoluble
– Soluble
• Many health organizations recommend
increasing intake of dietary fiber
**38 g/day for men
**25 g/day for women
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11
Focus on Dietary Fiber,
cont’d
• Sudden increases in fiber can result in
gas, bloating, and constipation
• Excessive amounts of dietary fiber can
trap small amounts of minerals and
prevent their absorption into the
gastrointestinal tract
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12
Summary of Dietary Fiber
Classes
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13
Energy Function of
Carbohydrates
• Basic fuel supply
– Energy for physical activities and all
work of body cells
• Reserve fuel supply
– Provided by stored glycogen
– Available to maintain a normal blood
glucose level
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14
Special Tissue Functions of
Carbohydrates
• Liver
– Stored glycogen protect cells from
depressed metabolic function
• Protein and fat
– Carbohydrates regulate proteins and
fat used for energy
• Heart
– Glycogen is vital emergency back up
fuel for heart muscle
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15
Digestible Food Sources of
Carbohydrates
• Central nervous system
– Brain dependent on minute-to-minute supply
of glucose
• Starches
– Provide fundamental complex carbohydrates
• Sugars
– Readily absorbed
– High-sugar diets carry health risks
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16
Teaspoons of High-Fructose
Corn Syrup Consumed
We eat too
much
sugar!
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17
Digestion of Carbohydrates
• Mouth
– Mechanical or muscle functions break
food mass into smaller particles
– Chemical digestion begins with salivary
amylase
• Stomach
– Peristalsis continues mechanical
digestive process
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18
Digestion of Carbohydrates,
cont’d
• Small intestine
– Peristalsis continues mechanical
digestion
– Pancreatic secretions - Pancreatic
amylase breaks starches down into
disaccharides and monosaccharides
– Intestinal secretions - Sucrase, lactase,
and maltase help break down their
starches
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19
Body Needs for
Carbohydrates
• Dietary Reference Intakes
– 45% to 65% of adult’s total caloric
intake should come from carbohydrate
foods
– Limit sugar to no more than 25% of
calories consumed
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20
Summary
• Carbohydrates are the primary source of
energy for most of the world’s population.
• Carbohydrates are distributed as the
plant sources: grains, legumes,
vegetables, and fruits.
• The two basic types of carbohydrates are
simple and complex.
• Simple carbohydrates are composed of
single- and double-sugar units
(monosaccharides and disaccharides)
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21
Summary, cont’d
• Complex carbohydrates are composed of
many sugar units.
• Dietary fiber is a complex carbohydrate
that is not digestible and is found mainly in
the structural parts of plants.
• Carbohydrate digestion begins in the
mouth, continues in the stomach, moves to
the small intestine, and finally arrives in the
large intestine and exits through the anus.
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22
FATS -Key Concepts
• Dietary fat supplies essential body tissue
needs, both as an energy fuel and a
structural material.
• Foods from animal and plant sources
supply distinct forms of fat that affect
health in different ways.
• Excess dietary fat, especially from animal
food sources, is a negative risk factor in
overall health.
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23
The Nature of Fats
• Dietary importance
– Concentrated fuel for energy
• Classes of fats
– Lipids
– Glycerides
• Triglycerides
– Fatty acids
– Lipoproteins
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24
Fatty Acids
• ESSENTIAL fatty acids means that it is ESSENTIAL
that we eat them
• Saturated fatty acids
– Filled or “saturated” with hydrogen
• Unsaturated fatty acids
– Omega 3 and omega 6
– Not completely filled with hydrogen
– Less heavy, less dense
– Monounsaturated: one unfilled spot
– Polyunsaturated: two or more unfilled spots
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25
Phospholipids
• Triglyceride derivative: third fatty acid
replaced by phosphate group
• Partially hydrophobic, partially
hydrophilic – remember cell wall?
• Allow transport of fats through
bloodstream
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26
Cholesterol
• Not a fat
• A fat-related compound
– Only from animal foods
• Egg yolks
• Liver, kidney
• Meats
– Synthesized in the liver
– Diet should be low in cholesterol
– Linked with heart disease
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27
Functions of Fat in Foods
• Fat in foods provide:
– Energy
– Essential nutrients
– Flavor and satisfaction
– Fat substitutes are not absorbed and
therefore do not provide energy or
essential nutrients but may provide
flavor and satisfaction
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28
Functions of Fat in the Body
• Adipose tissue
– Protects organs
– Helps regulate temperature
• Cell membrane structure
– Forms part of cell membrane
– Helps transport nutrients across cell
membranes
• Second choice to achieve energy
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29
Food Sources of Fat
• Animal fats
• Plant fats
• Hydrogenated fats (trans fats)
– Commercial fat products raise health
concerns
– Food industry now offers trans-free
products
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30
A QUESTION FOR YOU!
• Why are trans fats “worse” than
saturated fats?
• Studies show they lower HDL
cholesterol and raise LDL
cholesterol, whereas saturated fats
only raise LDL cholesterol, leaving
HDL the same or better
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31
FDA Health Claims
• Claims that link one or more dietary
components to the reduced risk of a
specific disease need to be
approved by the FDA
– Fat and cancer
– Saturated fat and cholesterol and heart
disease
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32
Key Concepts
• Dietary fat supplies essential body tissue
needs, both as an energy fuel and a
structural material.
• Excess dietary fat, especially from animal
food sources, is a negative risk factor in
overall health.
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33
Dietary Fat and Health
• The American diet is high in fat.
• Excess calories are stored as fat.
• Animal food sources contribute to excess
cholesterol and saturated fat in the diet.
• A decrease in saturated fat reduces
serum total cholesterol.
• Monounsaturated fats reduce LDL
cholesterol when substituted for
saturated fat.
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34
Digestion of Fats
• Mouth - mechanical
• Stomach - mechanical
• Small intestine – chemical & mechanical
– Bile from the gallbladder
– Enzymes from the pancreas
– Enzymes from the small intestine
– Absorption
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35
Dietary Fat Requirements
• Healthy diet guidelines:
– Stress the health benefits of a diet low in
fat overall, but more so with saturated fat,
and cholesterol
– Recommend that the fat content should
not exceed 20% to 35% of total kilocalories
• Less than 10% of kilocalories should be
from saturated fat
• Dietary cholesterol should be limited to
300 mg/day
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36
Dietary Guidelines for
Americans
• Control saturated fat and cholesterol
• Use only lean cuts of all meats; use more poultry
and seafood (shellfish are low in fat but high in
cholesterol)
• Limit eggs to two or three per week
– Can discard the yolk to decrease fat
• Use low-fat or fat-free milk and milk products
• Avoid adding too much fat in food preparation –
food should not slide across the plate!
Mosby items and derived items © 2006 by Mosby, Inc.
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37
Slide 37
Summary
• Classes of fat include lipids, triglycerides, fatty
acids, and lipoproteins
• Fatty acids can be saturated or unsaturated
• Essential fatty acids are necessary to aid in tissue
strength, muscle tone, cholesterol metabolism,
blood clotting, and heart action
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38
Summary, cont’d
• Cholesterol is a sterol only found in animal
foods that is vital in human metabolism
• Digestion of fat includes digestive agents
such as bile and pancreatic lipase
• Fatty acids and glycerides are incorporated
into chylomicrons and absorbed via the
lymphatic system into the bloodstream
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39