Transcript HUMAN NUTRITION

HUMAN NUTRITION
The basic nutritional needs
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Supply energy and raw materials for activities and
processes in the body
 Macronutrients - required in large amounts:
• carbohydrates
• proteins
• fats
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Micronutrients - required in small amounts:
• vitamins
• minerals
Uses of macronutrients
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Carbohydrates and fats used as a source of energy
(protein can also be used for this)
 Proteins provide the raw materials, or building
blocks, required for the synthesis of essential
metabolites, growth, and tissue maintenance - to
make human proteins
 Carbohydrates and proteins: 4 calories/gram
 Fat: 9 calories/gram
Carbohydrates
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Monosaccharides
• Simple sugars
• Building block of more complex carbohydrates
• Glucose - the most abundant
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Disaccharides
Polysaccharides
• starch, glycogen
• cellulose
Glucose
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During digestion other carbohydrates are
broken down or converted to glucose
Transported by the blood to all the cells in
the body
Within cells, respiration breaks down
glucose to produce energy necessary to
sustain life
Other monosaccharides
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Fructose and galactose have the same
chemical make up as glucose, C6H12O6,
differing only in the arrangement of the
atoms
Converted into glucose and metabolized
High fructose corn syrup, often preferred
because sweeter than sucrose
Disaccharides
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Two monosaccharides chemically joined
 Sucrose - most common (glucose and fructose)
• Table sugar at least 97% pure sucrose
• Supplies only calories - no other nutritional value
• During digestion broken into glucose and fructose
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Other disaccharides
• Lactose - milk sugar (glucose and galactose)
• Maltose (2 glucose molecules) - germinating grains
Polysaccharides
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Also known as complex carbohydrates
Hundreds to thousands of sugar units
Glucose is the only monosaccharide
Distinguished by the way in which the
glucose units are joined together, their
arrangement, and their number
Starch
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Storage form of glucose found in plants
• Seeds, some fruits, tubers, and tap roots
• Starch in foods can be traced directly to plant origin:
starch in bread or pasta from wheat
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Starch in the human diet
• Grains (wheat, rice, and corn)
• Underground crops (potato, sweet potato, & cassava)
• Legumes (beans and peas)
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Broken down into glucose by enzymes
Glycogen
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Body's storage form of glucose in liver and
skeletal muscles
Excess glucose is stored as glycogen
Only a day’s worth of glycogen is stored
Carbohydrate loading: eat lots of starchy
foods to build glycogen reserves
Excess glucose beyond this is generally
converted to fat
Fiber - other polysaccharides
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From plant sources
Not digestible - provides bulk and other
benefits
Fruits, vegetables, seeds and whole grains
supply most of the fiber in the human diet.
Types of dietary fiber
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Cellulose
Lignin
Hemicellulose
Pectin
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Gums
Mucilages
Others
Cellulose
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Principal component of plant cell walls
Composed of glucose
Humans do not have the enzymes to break
the bonds connecting the glucose molecules
in cellulose
Passes through the digestive tract as
roughage
Other fibers
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Pectins and hemicelluloses - also cell wall
polysaccharides
Pectins also occur in the middle lamella
Gums and mucilages are exudates from
plants that are used commercially as
thickening agents
Polysaccharides from red and brown algae
are also dietary fiber
Dietary fiber grouped into two types
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Soluble and insoluble - relates to their
solubility in water
Insoluble fiber includes cellulose and lignin
and some hemicelluloses
Soluble fiber includes other hemicelluloses,
pectins, gums, mucilages, and algal
polysaccharides
Soluble fiber & Insoluble fiber
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Gum in oat bran
 Pectin in apples
 Believed to lower
cholesterol levels in
the blood
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Wheat bran
Largely cellulose
No cholesterol
lowering ability
Effective in speeding
passage of food
through the large
intestines
May reduce the risk of
colon cancer
Proteins and essential amino acids
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Proteins are large complex molecules
composed of amino acids
20 naturally occurring amino acids
Thousands of different types of proteins
During digestion proteins in our food are
broken down into the component amino
acids by enzymes in the digestive tract and
transported in the blood stream
Functions of Proteins
Type Protein Function
Structural
Enzymes
Hormones
Transport
Storage
Contractile
Defensive
Support
Catalysts
Regulation
Transport
substances
Storage of
amino acids
Movement
Protection
Examples
Collagen and keratin
Digestive enzymes
Insulin
Hemoglobin
Ovalbumin in egg white
Casein in milk
Actin, myosin - muscles
Antibodies
Essential Amino Acids
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Role of dietary protein is to supply amino acids
for the body to make human proteins
All 20 amino acids are necessary for protein
synthesis
Human body can synthesize 11 amino acids
Other nine cannot be made by the body and must
come from the diet
These nine are called essential amino acids
Essential Amino Acids
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Cannot be stored by the body at all
They must be present simultaneously in the
diet
It is critical to receive all the essential
amino acids in each meal
Persistent lack of these essential amino
acids results in protein deficiency
Complete proteins
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Complete proteins contain all the essential
amino acids and in the right proportions
Almost all proteins derived from animals
are complete proteins
Proteins derived from plants are usually
incomplete, deficient in one or more
essential amino acids
Complementary plant proteins
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Combining complementary plant proteins
can supply all essential amino acid
Traditional diet of the Mexican Indians,
beans and corn, contains complementary
proteins
• The beans are low in methionine but adequate
in tryptophan and lysine
• Corn is poor in tryptophan and lysine but
contains adequate amounts of methionine
Essential and Nonessential
Amino Acids
Essential
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Nonessential
Alanine
Asparagine
Aspartic Acid
Arginine
Cysteine
Glutamic Acid
Glutamine
Glycine
Proline
Serine
Tyrosine
How much protein do we need?
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Nutritional recommendations can be based
on two criteria
• 12% of the total calories consumed should be
from proteins (1500 calories diet - 45 grams of
protein; 1800 calories - 54 g; 2000 cal - 60 g)
• 0.8 g/kg body weight (person weighing 150 lbs
-54 g protein; person weighing 100 lbs - 36 g
protein; 200 lbs - 72 g protein
How much protein in our food?
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1 ounce meat - 7 grams protein
• 4 ounces turkey - 28 grams protein
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1 ounce cheese - 7 grams protein
1 glass milk - 8 grams protein
1/2 cup beans - 6 grams protein
1 slice whole wheat bread- 4 grams protein
1 egg - 8 grams protein
2 TBSP peanut butter - 8 grams protein
1 serving oatmeal - 5 grams protein
Malnutrition
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Chronic hunger and malnutrition are problems in many
developing nations
Estimates: 15% to 20% of the world's population (around
one billion people) suffer from undernutrition or
malnutrition
Approximately 20 million deaths each year
Undernutrition is defined as an insufficient number of
calories to maintain daily energy requirements
Malnutrition is a quality deficiency in which one or more
essential nutrients is lacking even though enough
calories
Kwashiorkor
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Protein deficient but sufficient calories
Prevalent after weaning when a child no
longer receives protein-rich breast milk and
is switched to a starchy diet low in protein
Symptoms of kwashiorkor
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puffy skin
swollen belly due to edema
reddish-orange cast to the hair
dermatitis and listlessness.
Marasmus
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Results from starvation
Diet is low in calories and protein
Sufferers extremely thin and shriveled
(literally skin and bones)
Muscles of the body, even the heart muscle,
are wasted away as muscle protein is used
to supply energy needs
Treatment
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Symptoms of both marasmus and
kwashiorkor can be reversed if treated in
time
In infants and young children, mild mental
retardation and stunted growth may be
permanent results
Vegetarian Diets
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Ovo-lacto vegetarian
Lacto vegetarians
Vegans
Major difficulty is getting sufficient protein
Balance amino acids to avoid protein
deficiency
Fats
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One category of lipid
Lipids are a diverse group of compounds
with a common characteristic of insolubility
in water
Some fat is necessary in the diet - several
vital functions
Functions of Lipids
Type of Lipid Function Examples
Triglyceride
Steroid
Energy
storage
Insulation
Structural
Regulation
Phospholipid
Structural
Animal fat
Vegetable oils
Subcutaneous fat
Cholesterol in
membranes
Cortisol, Estrogen,
Testosterone
Phosphatidylcholine
in cell membranes
Triglycerides
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Fats and oils
95% of lipids in foods
Formed from glycerol and 3 fatty acids
Fatty acids
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Simplest type of lipid
Building blocks for triglycerides and
phospholipids
Body can synthesize most fatty acids
Three must be supplied in the diet
• Linoleic acid
• Linolenic acid
• Arachidonic acid
Fatty acid
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Carbon chain with hydrogen attached
Different fatty acids vary in the number of
carbon and hydrogen atoms
Saturated or unsaturated
• Saturated fatty acids have all single bonds
between carbon atoms
• Unsaturated fatty acids have one or more
double bonds
Saturated Fatty Acid
H H H H H H H H H H H H H H H
l l l l l l l
l l l l l l l l
O
H - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C-OH
l l
l l l
l l l l l l
l l l l
H H H H H H H H H H H H H H H
Monounsaturated Fatty Acid
H H H H H H H H H H H H H H H
l l l l l l
l
l l l l l l l l
O
H - C - C - C - C - C - C = C - C - C - C - C - C - C - C - C - C-OH
l l
l l l
l l l l
l l l l
H H H H H
H H H H H H H H
Polyunsaturated Fatty Acid
H H H H H H H H H H H H H H H
l l l l l
l l
l l l l l l l l
O
H - C - C - C - C - C = C - C - C - C - C = C - C - C - C - C - C-OH
l l
l l
l l l
l l l l
H H H H
H H H
H H H H
Triglycerides
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Glycerol backbone is common to all
Many types of fatty acids occur
Nature of the fatty acids determines the
properties of the triglyceride
Saturated Fat
C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C
Monounsaturated Fat
C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C
Polyunsaturated Fat
C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C
l
C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C
Fats in Foods
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Contain a mixture of both saturated and
unsaturated fatty acids
Saturated fats - contain mostly saturated
fatty acids
• solid at room temperature - animal fats such
as lard, butter, and beef fat
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Vegetable oils - generally composed of
unsaturated fatty acids
• liquid at room temperature
Vegetable Oils
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Oils with monounsaturated fatty acids
• olive oil, peanut oil, and canola oil
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Oils with polyunsaturated fatty acids
• corn oil, soybean oil, and safflower oil
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Saturated fats in plants
• coconut oil, palm oil, and cocoa butter
• consist mostly of saturated fatty acids
Hydrogenation
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In prepared foods with vegetable oils
Unsaturated oil has been chemically
modified by hydrogenation
Adds hydrogen making an unsaturated oil, a
saturated fat
Converts a liquid oil into a solid fat margarine
Saturated vs. unsaturated fats
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Diets high in saturated fats have been
implicated in colon, breast, and
prostate cancers
Saturated fats increase blood
cholesterol levels and are linked to
cardiovascular disease
Unsaturated fats lower the risk of
cardiovascular disease by lowering
blood cholesterol levels
Cholesterol
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Type of lipid known as steroid
• lipid containing four carbon rings
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Vital component of cell membranes
• therefore needed by all cells
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Used in the synthesis of sex hormones and
several other hormones
Cholesterol
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Synthesized in liver from saturated fatty
acids and absorbed from animal foods
• If the diet is high in saturated fats, even if it is
low in cholesterol, the liver responds by
increased cholesterol synthesis
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Lipoproteins: HDL and LDL
LDL - bad cholesterol causing deposits in
arteries and leading to heart attacks and
strokes
Cholesterol
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Diets high in cholesterol and/or saturated fat
contribute to high blood cholesterol levels
especially LDLs
Unsaturated fats lower blood cholesterol
levels
• Polyunsaturated fats lower all cholesterol levels
including HDLs
• Monounsaturated fats lowering total and LDL
levels
Micronutrients
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Essential for proper nutrition
Required in very small amounts
Deficiency symptoms develop when
nutrient is lacking
Comprise only 1 to 2% of the dry weight
There are two categories
• organic compounds - vitamins
• inorganic compounds - minerals
Dietary guidelines
1. Consume only as much energy (kcal) as is
expended
2. Increase consumption of complex
carbohydrates and "naturally occurring"
sugars from 28% of energy intake to 48%
3. Reduce consumption of refined and
processed sugars to account for about
10% of total energy intake
Dietary guidelines (cont’d)
4. Reduce fat consumption from
approximately 40% to about 30%
5. Reduce saturated fat consumption to
about 10% of energy intake;
polyunsaturated and monounsaturated
fats, should each account for 10%
6. Reduce cholesterol consumption to
about 300 mg a day
7. Limit sodium intake to about 5 g a day
Nutrition Facts
Serving Size 1/2 (127 g)
Servings Per Container About 3.5
Amount per Serving
Calories 100 Calories from Fat 0
% Daily Value*
Total Fat 0g
Saturated Fat 0g
Cholesterol 0mg
Sodium 580mg
Total Carbohydrates 19g
Dietary Fiber 5g
Sugars 3g
Protein 6 g
0%
0%
0%
24%
6%
20%
12%
Vitamin A 0% * Vitamin C 0%
Calcium 2% * Iron 8%