Perspectives in Nutrition, 8th Edition
Chapter 1 Outline: The Science of Nutrition
After studying this chapter, you will be able to:
1. Define the terms nutrition, carbohydrates, proteins, lipids (fats and oils), vitamins, minerals,
water, and calories.
2. Use the physiological fuel values of energy yielding nutrients to determine the total energy
content (calories) in a food or diet.
3. Describe the major characteristics of the North American diet and the food behaviors that often
need improvement.
4. Describe the factors that affect our food choices.
5. Discuss the components and limitations of nutritional assessment.
6. List the attributes of a healthful lifestyle that are consistent with the Healthy People 2010 goals.
7. Identify diet and lifestyle factors that contribute to the leading causes of death in North America.
8. Describe the role of genetics in the development of nutrition-related diseases.
9. Explain how the scientific method is used in developing hypotheses and theories in the field of
nutrition.
10. Identify reliable sources of nutrition information.
1.1
Nutrition Overview
A.
Nutrients
1.
General
a.
Nutrition: the science of food; the nutrients and the substances therein;
their action, interaction, and balance in relation to health and disease; and
the processes by which the organism ingests, digests, absorbs, transports,
utilizes, and excretes food substances
b.
Nutrients: substances essential for health that the body cannot make or
makes in quantities too small to support health
i.
Specific biological function
ii.
Removal from diet leads to decline in human biological function
iii.
Replacing before permanent damage occurs restores impaired
biological functions
c.
Categorizing nutrients by function
i.
Provide energy (most carbohydrates, proteins, most lipids)
ii.
Promote growth and development (proteins, lipids, some
vitamins, some minerals, water)
iii.
Regulate body processes (proteins, some lipids, some vitamins,
some minerals, water)
d.
Categorizing nutrients by needs
i.
Macronutrients: needed in gram quantities (carbohydrates, lipids,
proteins, water)
ii.
2.
3.
4.
5.
Micronutrients: needed in milligram or microgram quantities
(vitamins, minerals)
Carbohydrates
a.
Composed of carbon, hydrogen, and oxygen
b.
Primary dietary sources: fruits, vegetables, and grains
c.
Classified based on size
i.
Simple carbohydrates (sugars): sucrose, glucose
ii.
Complex carbohydrates (polysaccharides): starch, glycogen,
fiber
d.
Glucose is the major source of energy for most cells; provides 4 kcal/g
e.
Body can make glucose from complex carbohydrates or proteins
Lipids
a.
Composed of carbon, hydrogen, and oxygen
b.
Fats are solid at room temperature; oils are liquid at room temperature
c.
Dense source of energy; provide 9 kcal/g
d.
Insoluble in water; dissolve in certain organic solvents
e.
Chemistry of lipids
i.
Triglycerides (primary form of lipids in body): 3 fatty acids
attached to glycerol
ii.
Fatty acid: long chain of carbons flanked by hydrogens with
acid group at one end
iii.
Saturated: no double bonds; carbon chain is saturated with
hydrogen atoms; solid at room temperature; predominate in
animal fats; dietary intake should be minimized
iv.
Unsaturated: one or more carbon-carbon double bonds; liquid at
room temperature; predominate in plant oils
v.
Trans: unsaturated fats that have been processed to be solid at
room temperature; dietary intake should be minimized
f.
Essential fatty acids are not made by the body and must be supplied in
the diet
i.
Linoleic acid
ii.
Alpha-linolenic acid
Proteins
a.
Composed of carbon, oxygen, hydrogen, and nitrogen
b.
Body roles
i.
Structure
ii.
Blood components
iii.
Cell membranes
iv.
Enzymes
v.
Immune factors
vi.
Provide some energy (4 kcal/g)
c.
Formed by bonding of amino acids
Vitamins
a.
Organic (contain carbon)
b.
c.
d.
B.
1.2
Enable chemical reactions to occur in the body
Provide no energy, but participate in energy-yielding reactions
Fat-soluble (A, D, E, K)
i.
More likely than water-soluble vitamins to cause toxicity
e.
Water-soluble (thiamin, riboflavin, niacin, B-6, pantothenic acid, biotin,
folate, B-12, C)
i.
More susceptible than fat-soluble vitamins to destruction by
cooking
ii.
More readily excreted than fat-soluble vitamins
6.
Minerals
a.
Simple, inorganic structures
b.
Not destroyed by cooking, but may leach into cooking water
c.
Yield no energy
d.
Roles
i.
Nervous system function
ii.
Skeletal system structure
iii.
Water balance
e.
Major minerals: needed daily in gram amounts (e.g., sodium, potassium,
chloride, calcium, phosphorus)
f.
Trace minerals: needed daily in milligram or microgram amounts (e.g.,
iron, zinc, copper, selenium)
7.
Water
a.
Macronutrient needed in largest amounts by the body
b.
Roles
i.
Lubricant
ii.
Solvent
iii.
Transport medium
iv.
Temperature regulation
c.
Sources
i.
Dietary intake
ii.
By-product of metabolism
Phytochemicals and Zoochemicals
1.
Phytochemicals: physiologically active plant compounds in fruits, vegetables,
legumes, and whole grains
2.
Zoochemicals: physiologically active compounds found in animal products
3.
Potential health benefits
a.
Reduced risk of cancer
b.
Reduced risk of cardiovascular disease
4.
Dietary sources are superior to supplemental sources
5.
Table 1-2 lists examples of phytochemical compounds under study
Energy Sources and Uses
A.
Physiological fuel values
1.
Carbohydrates (4 kcal/g)
B.
C.
D.
E.
1.3
2.
Fats (9 kcal/g)
3.
Proteins (4 kcal/g)
4.
Alcohol (7 kcal/g); not essential
Uses
1.
Build new compounds
2.
Perform muscular movements
3.
Promote nerve transmission
4.
Maintain ion balance within cells
Calorie: amount of heat energy required to raise the temperature of 1 g of water 1°C
Food energy is usually expressed in kilocalories: amount of heat energy required to raise
the temperature of 1000 g of water 1°C
Energy in food can be measured by bomb calorimetry or estimated based on amount of
macronutrients present
The North American Diet
A.
General
1.
U.S. Department of Health and Human Services’ National Health and Nutrition
Examination Survey (NHANES) and surveys by Health Canada and Agriculture
and Agrifood Canada collect information on North American diets
2.
Typical macronutrient distribution of North American diets
a.
16% protein
b.
50% carbohydrates
c.
33% fats
3.
Overall calorie intake of many North Americans exceeds requirements
4.
Animal sources supply 2/3 protein intake, whereas plant sources dominate in
many other countries
5.
Half of dietary carbohydrates come from simple sugars; North Americans need to
reduce simple sugar intake
6.
60% of dietary fat comes from animal sources; many North Americans exceed
saturated fat and cholesterol recommendations
7.
North Americans should increase intake of vitamin A, vitamin E, iron, and
calcium
8.
North Americans should decrease intake of sodium
9.
Older adults consume inadequate vitamin D
10.
Women of childbearing age consume inadequate iron
11.
General food recommendations
a.
Reduce sugared soft drinks
b.
Reduce fatty foods
c.
Increase fruits
d.
Increase vegetables
e.
Increase whole grain breads
f.
Increase reduced-fat dairy products
g.
Multivitamin and mineral supplements may help to meet nutrient needs
but do not substitute for an overall healthy diet
B.
1.4
What Influences Our Food Choices?
1.
Hunger: physical need for food
2.
Appetite: desire to eat certain foods and reject others
a.
Flavor, texture, and appearance preferences
b.
Culture
c.
Lifestyle
d.
Routines and habits
e.
Food cost
f.
Environment
g.
Food marketing
h.
Health and nutrition concerns, knowledge, and beliefs
Nutritional Health Status
A.
General
1.
Optimal (desirable) nutrition status: body tissues have enough of a nutrient to
support normal functions as well as build and maintain surplus stores to be used
in times of increased need
2.
Undernutrition: nutrient intake does not meet nutrient needs, causing surplus
stores to be used
a.
Subclinical nutrient deficiency: nutrient stores are depleted, but person
exhibits no overt signs or symptoms of deficiency
b.
Clinical nutrient deficiency: signs and symptoms of nutrient deficiency
become outwardly apparent
i.
Sign: feature that can be observed (e.g., flaky skin)
ii.
Symptom: change in body function that may not be apparent to
health care provider (e.g., fatigue, ache)
3.
Overnutrition: nutrient intake exceeds nutrient needs
B.
Health Objectives for the United States for the Year 2010
1.
Healthy People 2010, issued in 2000 by US DHHS Public Health Service
2.
Main objective: promote healthful lifestyles to reduce preventable death and
disability
3.
Minority groups are a particular focus
4.
Table 1-4 lists nutrition-related objectives from Healthy People 2010
C.
Assessing Nutritional Status
1.
Background factors
a.
Family history
b.
Personal medical history
2.
Anthropometric assessments: measurement of aspects of the body
a.
Height
b.
Weight (weight changes)
c.
Body circumferences (e.g., waist, hips, arm)
d.
Skinfold thicknesses: indicator of body fatness
3.
D.
E.
1.5
Biochemical assessments: measurement of concentrations of nutrients and
nutrient by-products in blood, urine, and feces or measurement of enzyme
activities
4.
Clinical assessments: physical evidence of diet-related diseases
5.
Dietary assessments
a.
Food frequency
b.
Food history
c.
Typical intake
6.
Environmental assessment
a.
Educational background
b.
Economic resources
Limitations of Nutritional Assessment
1.
Many signs and symptoms are non-specific
2.
Signs and symptoms may be slow to develop
3.
Clinical evidence of poor nutritional health may be slow to develop
Importance of Being Concerned about Your Nutritional Status
1.
Healthy lifestyle practices reduce risk for many diseases
a.
Varied diet, rich in fiber, low in animal and trans fat, include fish
b.
Avoid becoming overweight
c.
Moderate alcohol consumption
d.
Exercise for at least 30 minutes daily
e.
Avoid smoking
2.
Figure 1-8 summarizes health problems associated with poor dietary habits
Genetics and Nutrition
A.
General
1.
Although foods and humans contain the same nutrients, the proportions differ
2.
Genes direct how nutrients are transformed and reassembled into body structures
and compounds
3.
Genes are only one factor that contribute to risk for diseases
4.
Genetic tests can detect gene mutations that affect risk for some illnesses
B.
Nutritional Diseases with a Genetic Link
1.
Most chronic nutrition-related diseases are influenced by interactions among
genes (i.e., family history), nutrition, and other lifestyle factors
a.
Diabetes (types 1 and 2)
b.
Some types of cancer (e.g., colon, prostate, breast)
c.
Osteoporosis
d.
Cardiovascular disease
i.
Cholesterol metabolism
ii.
Salt sensitivity (leading to hypertension)
e.
Obesity: regulation of body weight involves at least 250 genes
2.
Heredity ≠ destiny
C.
Your Genetic Profile
1.
D.
E.
1.6
Awareness of genetic predisposition for certain diseases allows an individual to
take preventative actions
2.
Construct a family tree of illnesses and deaths (genogram)
a.
High risk: more than one first-degree relative with disease, particularly if
developed before age 50 or 60
Gene Therapy
1.
Use virus to incorporate normal DNA into mutated cells
2.
New technology; still requires approval by FDA
Genetic Testing
1.
Provides opportunity for gene therapy
2.
Allows couples with genetic diseases to make informed choices about having
children
3.
Fosters early diagnosis and individualized treatment
4.
Limitations
a.
Not all diseases may be detected
b.
Genetic susceptibility doesn’t guarantee development of a disease
c.
Gene therapy is not widely available; only treatment for disease after it
develops
d.
Possible job and medical insurance discrimination
e.
Unnecessary radical medical treatments
f.
Depression
5.
Genetic counselors analyze family history and evaluate risks
Using Scientific Research to Determine Nutrient Needs
A.
General
1.
Nutrition knowledge has been gained through research using the scientific
method
a.
Observations
b.
Hypotheses
c.
Experimentation
d.
Incorrect explanations are rejected; likely explanations form basis for a
model
e.
Research results are scrutinized by peers
f.
Results are confirmed by additional research
2.
Scientific theories, laws, and discoveries always should be subjected to challenge
and change
B.
Making Observations and Generating Hypotheses
1.
Examples:
a.
Vitamin C and scurvy
b.
Niacin and pellagra
2.
Epidemiology: study of diseases in populations
C.
Laboratory Animal Experiments
1.
Human experiments are most convincing, but not always feasible or ethical
2.
Animal model: disease in laboratory animals that mimics human disease
D.
1.7
Human Experiments
1.
Human and animal research must be reviewed and approved by a research review
board to ensure that it:
a.
Has a valid experimental protocol
b.
Is expected to produce important knowledge
c.
Will treat study participants fairly and ethically (e.g., informed consent)
2.
Migrant studies: examine changes in health of people who move from one
country to another
3.
Cohort studies: follow a healthy population over time to examine development of
diseases
4.
Case-Control Study
a.
Compare individuals with a disease/condition (cases) with individuals
who do not have the disease/condition (controls)
b.
Cases and controls should be matched for other traits (e.g., age, race,
gender)
c.
Can provide clues that lead to hypotheses, but cannot prove cause and
effect
5.
Double-Blind Study
a.
Compares group receiving a treatment (experimental group) with group
receiving a placebo (control group)
b.
Placebo: fake treatment
c.
Random assignment of study participants to experimental or control
groups
d.
Double-blind: identities of treatments are not known by study
participants or researchers; controlled by third-party
i.
Reduces risk of researcher bias
ii.
Reduces risk of placebo effect: control group experiences
changes that cannot be explained by the action of the placebo
6.
Peer Review of Experimental Results
a.
Ensures that only the most unbiased, objective findings from carefully
designed and executed research studies are published
b.
Science presented in peer-reviewed journals is more reliable than
information presented by other media sources
7.
Follow-Up Studies
a.
One experiment is never enough to prove a hypothesis or provide a basis
for nutrition recommendations
b.
Results must be confirmed by other researchers, under varying
conditions, in various populations
Evaluating Nutrition Claims, Products, and Advice
A.
General
1.
Apply basic nutrition principles to any nutrition claim
2.
Be wary of claims that:
a.
Only discuss advantages and ignore possible disadvantages
b.
c.
d.
e.
B.
C.
Purport a new or secret scientific breakthrough
Offer to cure a disease
Sound too good to be true
Express extreme bias against the medical community or traditional
medical practices
3.
Examine scientific credentials
4.
Note quality of research studies used to support a claim
5.
Be wary of press conferences and other hype
Buying Nutrition-Related Products
1.
Many claims for popular nutrition-related products are unsubstantiated
2.
Dietary Supplement Health and Education Act (DSHEA) of 1994 classified
vitamins, minerals, amino acids, and herbal remedies as “foods,” so that FDA
cannot regulate them as strictly as medications
3.
FDA does not have the resources or authority to challenge every supplement
claim
4.
Federal Trade Commission may investigate dubious claims
5.
Supplement industry is trying to implement self-policing procedures
6.
Buyer beware, particularly for off-label uses
7.
Allowable claims
a.
General well-being
b.
Prevention of nutrient deficiency
c.
Structure/function claims
i.
Maintains bone health
ii.
Improves blood circulation
8.
Disclaimer: “This statement has not been evaluated by the Food and Drug
Administration. This product is not intended to diagnose, treat, cure, or prevent
disease.”
Getting Nutrition-Related Advice
1.
Registered dietitians are a reliable source of nutrition advice
a.
Rigorous baccalaureate degree program
b.
Supervised professional practice
c.
Registration examination
2.
What to expect from a consultation with an RD or RDN
a.
Questions about medical history, lifestyle, and eating habits
b.
Formulation of an individualized diet plan
c.
Follow-up to track progress, answer questions, enhance motivation
d.
Involve family members in diet plan, when appropriate
e.
Interaction with physician