Chapter 11
Nutrition
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What are the components of food, and what are their effects on our
health?
What practical information can we glean from food labels?
How safe is our food supply?
What are the environmental implications of agricultural practices?
How do we feed our hungry and ever-expanding world population?
Calories
Remember: Calories are often used to express the energy released when
food is metabolized.
1 calorie (cal) is the amount of energy required to raise the temperature of
1.0 g of water by 1oC.
1 cal = 4.184 joules (J)
This is a small quantity of energy, so we typically use kilocalories (kcal):
1 kcal = 1,000 cal = 1 Calorie (C)
©McGraw-Hill Education.
Useful Terms
Malnutrition is caused by a diet lacking in the proper mix of nutrients, even
though the energy content of the food eaten may be adequate.
Undernourishment is experienced when the daily caloric intake is insufficient
to meet the metabolic needs of a person.
Although there are cases of malnourished and undernourished people in the
U.S., 69% of the adult population is classified as overweight with almost half
of that population classified as obese.
Obesity and its related adverse health effects are overtaking smoking as the
No. 1 cause of death in the United States.
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Food Labels
Processed foods in the U.S.
must list nutritional
information on their labels.
These labels provide
information regarding the
macronutrient content, such
as fats, carbohydrates, and
proteins.
Information regarding the
energy content (Calories), as
well as the concentration of
vitamins and minerals are also
listed on food labels.
©McGraw-Hill Education.
We Are What We Eat!
Food
Water
Fat
Carbohydrate
Protein
White bread
37
4
48
8
2% milk
89
2
5
3
Chocolate chip cookies
3
23
69
4
Peanut butter
1
50
19
25
Sirloin steak
57
15
0
28
Tuna fish
63
2
0
30
Black beans (cooked)
66
<1
23
9
But, how does this compare to the composition of our bodies?
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% Composition of
the Human Body
Human bodies consist mainly
of water, followed by proteins
and fats.
Minerals, carbohydrates, and
vitamins only make up about
8% of the human body.
On average, a 150-pound
person will contain 90 pounds
of water, and 30 pounds of
fat.
©McGraw-Hill Education.
Fats and Oils
Properties of fats: greasy, slippery, soft, low-melting, water insoluble solids.
Butter, cheese, cream, whole milk, and certain meats and fish are loaded with
them. All of these products are of animal origins.
But margarine and some shortenings are evidence that fats can also be of
vegetable origin. Oils, such as those obtained from olives, corn, or nuts,
exhibit many of the properties of animal-based fats, but in liquid form.
Molecules of fats and oils are both triglycerides, which contain three ester
functional groups:
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Types of Lipids
Fats are triglycerides that are
solid at room temperature,
whereas oils are triglycerides that
are liquid at room temperature.
Triglycerides belong to the lipid
family, a class of compounds that
includes cholesterol and other
steroids, including some complex
compounds such as lipoproteins
that contain fatty segments.
Triglycerides are formed from the
reaction between three fatty
acids and the alcohol glycerol.
©McGraw-Hill Education.
Fatty Acids
Fatty acids are characterized by two structural features:
1. A long hydrocarbon chain generally containing an even number of carbon atoms
(typically 12 to 24)
2. A carboxylic acid group (–COOH, or –CO2H) at the end of the chain
©McGraw-Hill Education.
Triglyceride Formation
The formation of a triglyceride is made from 3 molecules of stearic acid and
one glycerol molecule:
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Saturated vs.
Unsaturated Fatty Acids
Saturated fatty acids contain only
C-to-C single bonds between the
carbon atoms.
A fatty acid is unsaturated if the
molecule contains one or more Cto-C double bonds between
carbon atoms.
©McGraw-Hill Education.
Properties of Fatty Acids
Name
Number of Carbon
Atoms per Molecule
Number of C=C Double
Bonds per Molecule
Melting Point
(C)
Capric acid
10
0
32
Lauric acid
12
0
44
Myristic acid
14
0
54
Palmitic acid
16
0
63
Stearic acid
18
0
70
Oleic acid
18
1
16
Linoleic acid
18
2
-5
Linolenic acid
18
3
-11
Saturated
Unsaturated
©McGraw-Hill Education.
Oils and Fats
Our bodies can synthesize
most any fatty acid from the
foods we eat, except linoleic
and linolenic acids, which
must be present in our diets.
Flaxseed oil is rich in linolenic
acid. Sunflower, corn, sesame,
and soybean oils are good
sources of linoleic acid.
Palm kernel, cocoa butter,
and coconut oils contain
much more saturated fat than
safflower, canola, flaxseed,
sunflower, corn, olive,
sesame, and soybean oils.
©McGraw-Hill Education.
Partially Hydrogenated Fats
Hydrogenation reduces C=C bonds to C-C bonds; H2 is added across the double bond.
A metal catalyst is required.
The number of double bonds in the fatty acid decreases, and it is transformed from an
oil into a semisolid fat.
The hydrogenation can be controlled to yield products with desired melting point,
softness, and spreadability. Double bonds are more susceptible to oxidation, which
leads to loss of shelf life.
©McGraw-Hill Education.
Trans Fats
In a cis isomer, H atoms are on the same side of the double bond.
In a trans isomer, H atoms are on the opposite side of the double bond. Trans fats
raise the level of triglycerides and “bad” cholesterol in the blood, leading to heart
disease. The molecular shapes of trans fatty acids are similar to saturated fats.
©McGraw-Hill Education.
Hydrogenation
Without Trans Fats:
Interesterification
An alternate to hydrogenation that will
not produce trans fats, scrambles fatty
acids on two or more triglycerides.
If you perform this process with a lowmelting triglyceride (an oil) and a highmelting point triglyceride (a fat), the
result is a mixture with an
intermediate melting point (a
semisolid fat).
This process uses a catalyst such as a
base or an enzyme.
©McGraw-Hill Education.
Carbohydrates
Carbohydrates are compounds containing carbon, hydrogen, and oxygen. The best known
dietary carbohydrates are sugars (like glucose) and starch. Carbohydrates have a 2:1 ratio of H to
O atoms (like water).
Monosaccharides, such as glucose and fructose, consist of a single ring. The difference between
alpha and beta glucose arises from the position of a single hydroxyl group.
©McGraw-Hill Education.
Disaccharides
Sucrose (table sugar) is an example of a disaccharide, formed by joining two
monosaccharide units.
In forming a sucrose molecule, an alpha-glucose and beta-fructose are connected by a
C-O-C linkage, formed when a water molecule is produced. This is another type of
condensation reaction, which was described in Chapter 9 for the synthesis of
polyesters.
©McGraw-Hill Education.
Polysaccharides
When many sugars are linked together you have polysaccharides, which are natural
polymers.
Because the single sugars can be either a or b, two different linkages arise. When
glucose polymerizes:
an a—linkage makes starch
and a b—linkage makes cellulose
©McGraw-Hill Education.
Starch vs. Cellulose
Starch is the primary carbohydrate component of several foods such as
potatoes.
Cellulose is the primary fibrous component in the cell walls of plants.
Glycogen has a similar structure as starch, and is the polysaccharide form of
carbohydrate that is stored in our bodies; this is our storehouse of energy.
We humans are able to digest starch, but we lack the enzymes required to
digest cellulose.
©McGraw-Hill Education.
Sweetness Value of Natural and Synthetic Sweeteners
Below are approximate relative sweetness values for natural (top) and synthetic
sweeteners (bottom). These values are compared to sucrose, with a value of 100.
There is concern about the health impacts of the amount of sweeteners that people
consume per day.
©McGraw-Hill Education.
Lactose
Maltose
Glucose
Honey
Sucrose
Fructose
16
32.5
74.3
97
100
173
Acesulfame
potassium
Aspartame
Neotame
Saccharin
Sucralose
200
200
7,000–
13,000
300
600
New Food Label Requirements
In order to more clearly identify the added sugar content of food (as well as trans fats
and other minerals), the U.S. Food and Drug Administration (FDA) has recently
proposed new labels, which will soon appear on food products in a supermarket near
you.
©McGraw-Hill Education.
Proteins
Proteins are an essential part of every living cell. They are also major components in
hair, skin, and muscle; and they transport oxygen, nutrients, and minerals through the
bloodstream.
Many of the hormones that act as chemical messengers are proteins, as are all the
enzymes that catalyze the chemistry of life.
Proteins are polyamides or polypeptides, polymers made up of amino acid monomers.
The great majority of proteins are made from various combinations of the 20 different
naturally occurring amino acids.
The general formula for an amino acid includes four groups attached to a carbon
atom: (1) a carboxylic acid group, -COOH; (2) an amine group, -NH2; (3) a hydrogen
atom, -H; and (4) a side chain designated as R.
©McGraw-Hill Education.
Naturally Occurring Amino Acids
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Amino Acid Side Chain Groups
Amino acid side chains may be polar or nonpolar. Nonpolar groups tend to be
hydrophobic, meaning they associate with one another to avoid interaction
with water.
Hydrophobic groups interact via London dispersion intermolecular forces.
Polar side groups may interact via hydrogen bonding intermolecular forces, or
via the attraction of ionic charges – especially groups that contain acidic or
basic groups (such as carboxylic acids or amines, respectively).
©McGraw-Hill Education.
Peptide Bonds
Two amino acids can link together via a peptide bond.
The two molecules join, expelling a molecule of water.
The process may repeat itself over and over, creating a peptide chain.
Once incorporated into the peptide chain, the amino acids are known as
amino acid residues.
©McGraw-Hill Education.
Essential Amino Acids
Protein formed depends both on the amino acids present and the sequence of those
amino acid residue in the peptide
Food needs to be ingested regularly to replenish the protein in the body, and these are
constantly broken down and reconstructed
Some amino acids (essential amino acids) cannot be synthesized by humans, so must
be ingested in our diet
The essential amino acids include histidine, lysine, threonine, isoleucine, methionine,
tryptophan, leucine, phenylalanine, and valine.
©McGraw-Hill Education.
Vitamins
Vitamins are defined by their properties:
• They are essential in the diet, although required in very small amounts.
• They all are organic molecules with a wide range of physiological
functions.
• They generally are not used as a source of energy, although some of them
help break down macronutrients.
• Some vitamins contain hydrocarbon chains and are fat-soluble, whereas
others have hydroxyl groups and are water-soluble (“like dissolves like”).
©McGraw-Hill Education.
Minerals
Minerals (either ions or inorganic compounds) are essential for good health.
In the body, metallic elements typically exist as cations (positive charge), and the
nonmetals usually occur as anions (negative charge).
The important, essential minerals are shown on this periodic table:
©McGraw-Hill Education.
Food for Energy
We get energy from the food we eat: fats, carbohydrates, and proteins.
This energy initially arrives on Earth in the form of sunlight, and is absorbed by green plants.
During photosynthesis, carbon dioxide and water are stored for forming glucose (C6H12O6):
Energy (from sunshine) + 6 CO2 + 6 H2O
chlorophyll
C6H12O6 + 6 O2
During respiration, the outcome from photosynthesis is reversed. Glucose is converted into
simpler substances (carbon dioxide and water in most cases), and energy is released:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy
©McGraw-Hill Education.
Energy Content of Macronutrients
The “burning” of fats, carbohydrates, and proteins in our body results in differing amounts of
energy. For instance, a fat contains about 9 Calories per gram, whereas carbohydrates or proteins
contain 4 Calories per gram:
C12H24O2 (lauric acid) + 17 O2 → 12 CO2 + 12 H2O + 8.8 Cal/g
C12H22O11 (sucrose) + 12 O2 → 12 CO2 + 11 H2O + 3.8 Cal/g
Since sugar is more “oxygenated” than a fatty acid, it releases less energy. This was also observed
for oxygenated fuels (Chapter 5), such as ethanol, relative to hydrocarbon-based fuels.
©McGraw-Hill Education.
Calorie Requirements
Age (yr)
Sedentary
Moderately Active
Active
14–18
1,800
2,000
2,400
19–30
2,000
2,000–2,200
2,400
31–50
1,800
2,000
2,200
51+
1,600
1,800
2,000–2,200
14–18
2,200
2,400–2,800
2,800–3,200
19–30
2,400
2,600–2,800
3,000
31–50
2,200
2,400–2,600
2,800–3,000
51+
2,200
2,200–2,400
2,400–2,800
Females
Males
©McGraw-Hill Education.
Energy Expenditures for Common Physical Activities
The basal metabolic rate (BMR) is the minimum amount of energy required daily to
support basic body functions. This corresponds to approximately 1 Calorie per
kilogram (2.2 pounds) of body mass per hour, although this varies with size and age.
Moderate Physical
Activity
Calories/hour
Vigorous Physical
Activity
Calories/hour
Hiking
370
Running
1,050
Light gardening
245
Heavy yard work
440
Dancing
315
Swimming
510
Golf
245
Aerobics
480
Bicycling (< 10 mph)
279
Bicycling (12–14 mph)
559
Walking (3.5 mph)
196
Jogging (5 mph)
490
Weight lifting
140
Weight lifting
(vigorous)
350
Stretching
105
Basketball
490
©McGraw-Hill Education.
Food Safety
400,000 – 500,000 deaths occur every year in the U.S. due to unhealthy eating and
inactivity.
Dietary suggestions have been identified to prevent diet-related diseases such as
hypertension (high blood pressure), heart disease, liver disease, cancer, stroke,
diabetes, and obesity.
Every year, more than 3,000 deaths and 150,000 cases of food poisoning due to the
presence of foodborne illnesses, the presence of bacteria, viruses, parasites, and
chemical toxins.
Three common policing methods are used to determine whether levels of food
contaminants exceed the limits established by law:
•
Food surveillance
•
Total diet surveys
•
Enforcement sampling
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World Average Meat Consumption
The Real Costs of Food Production
Water
•
Pumping water for irrigation depletes aquifers
•
Rivers dry up down stream if irrigating upstream
•
Increased BOD from fertilizer runoff
Pollution
•
Waste from crop residues and livestock
•
Insecticide and herbicide contamination
Land
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•
Erosion of topsoil
•
Lost of forest when cleared for farmland
Land and Grain Estimates for Food Production
Foods differ in the amount of land required to produce them:
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Meat Consumption and Production
The consumption (left) and production (right) of meat is increasing globally. It is
estimated that 358 kg of grain per person will be required by the year 2030. Assuming
a world population of 8 billion people, this would require 2.9 trillion kilograms of grain
to produce this much meat.
©McGraw-Hill Education.
Eating Locally
1.
Eating local means more for the local economy. A dollar spent locally generates twice as
much income for the local economy. When businesses are not owned locally, money leaves
the community with every transaction.
2.
Locally grown produce is fresher and tastes better. Produce at your local farmer's market
often has been picked within 24 hours of your purchase. This freshness not only affects the
taste of your food but also the nutritional value. Have you ever tried a tomato that was
picked within 24 hours?
3.
Locally grown fruits and vegetables have longer to ripen. Because the produce is handled
less, locally grown fruit does not have to stand up to the rigors of shipping. You will get
peaches so ripe that they fall apart as you eat them, and melons that were allowed to ripen
on the vine until the last possible minute.
4.
Buying local food keeps us in touch with the seasons. By eating with the seasons, our
foods are at their peak taste and less expensive.
5.
Supporting local providers supports responsible land development. When you buy locally,
you give those with local open space—farms and pastures—an economic reason to resist
further development.
©McGraw-Hill Education.
The Carbon Footprint of Food Production
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Carbon Dioxide Emissions from Food Production
Some foods have higher carbon footprints than others. Steak and cheese are
highest since these require agricultural practices for grain production.
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The Nitrogen Footprint of Foods
The nitrogen cycle represents a set of chemical pathways whereby nitrogen moves through the
biosphere. Plants such as alfalfa, beans, and peas “fix” (remove) nitrogen from the atmosphere.
Nitrogen-fixing bacteria convert nitrogen gas into ammonia, NH3. When ammonia dissolves in
water, it is converted to the ammonium ion, NH4+. Other reactive forms of nitrogen such as
nitrate (NO3-) are formed from ammonia via the process of nitrification.
©McGraw-Hill Education.
Fertilizers
Reactive forms of nitrogen are needed for plant growth. Bacteria in soils cannot supply ammonia,
ammonium ions, or nitrate ions in the amounts needed for optimal plant growth.
Hence, fertilizers must be used. The Haber-Bosch process allows for the economical production
of ammonia, which enabled the large-scale production of fertilizers.
The amount of reactive nitrogen from various sources has dramatically increased in recent years:
©McGraw-Hill Education.
Food Security
Food security deals with three primary issues:
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Food availability: having sufficient quantities of food available on a consistent basis.
•
Food access: having sufficient resources to obtain appropriate foods for a nutritious diet.
•
Food use: appropriate use of food based on knowledge of basic nutrition and care, as well as
adequate water and sanitation.
Undernourishment refers to the number of people who are unable to consume enough food to
conduct an active and healthy lifestyle. Undernourishment rates have decreased dramatically in
most parts of the world from 25 years ago, except in western Asia:
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