Nutrition

Chapter 1 — The Science of Nutrition: Factors That Influence Health

1. What Is Nutrition?

Nutrition

• Science of food

• Studies:

  • Nutrient actions

  • Nutrient interactions

  • Nutrient balance

  • Relationship between nutrients, health, and disease

• Includes:
  Ingestion → Digestion → Absorption → Transport → Utilization → Excretion

• Food provides nutrients needed to:

  • Fuel cells

  • Build cells

  • Maintain cells

Why nutrition matters

Many leading causes of death in the U.S. are influenced by:

• Poor diet

• Excessive energy intake

• Inadequate physical activity

2. Nutrients

Nutrient

A chemical substance found in food that the body uses to:

• Grow

• Survive

• Reproduce

• Provide energy

• Maintain life

Essential nutrient

A nutrient that:

1. Has a specific biological function

2. The body cannot make or cannot make enough of

3. Not getting enough causes a decline in normal function

4. Adding it back can restore normal function before permanent damage occurs

6 Classes of Essential Nutrients

1. Carbohydrates

2. Proteins

3. Lipids (fats)

4. Water

5. Vitamins

6. Minerals

Macronutrients vs. Micronutrients

3. Carbohydrates

Main facts

• Made of carbon, hydrogen, and oxygen

• Main sources:

  • Fruits

  • Vegetables

  • Grains

  • Beans

• Provide 4 kcal/g

• Major energy source for most cells

Types

Simple carbohydrates

• Table sugar (sucrose)

• Blood glucose

Complex carbohydrates

• Starch

• Glycogen

• Fiber

Important terms

• Monosaccharides = single sugars

• Disaccharides = two sugars

• Polysaccharides = many sugars

4. Lipids

Main facts

• Made mostly of carbon, hydrogen, and oxygen

• Insoluble in water

• Provide 9 kcal/g

• More energy-dense than carbohydrates and protein

Fat vs. Oil

• Fat: mostly saturated fatty acids → usually solid at room temperature

• Oil: mostly unsaturated fatty acids → usually liquid at room temperature

Triglycerides

The major form of fat in food and the body.

Functions:

• Major energy source

• Major form of stored energy

Structure:

• 3 fatty acids + 1 glycerol backbone

Saturated fats

• Usually solid at room temperature

• Mostly from animal sources

• Can raise blood cholesterol

• Associated with cardiovascular disease

Unsaturated fats

• Usually liquid at room temperature

• Mostly from plant sources

• Generally considered healthier than saturated fats

Remember:

Carbs = 4 kcal/g
Protein = 4 kcal/g
Fat = 9 kcal/g

5. Protein

Main facts

• Made of carbon, oxygen, hydrogen, and nitrogen

• Made of chains of amino acids

• Provides 4 kcal/g

Functions

Proteins are important structural/functional components of:

• Bone

• Muscle

• Blood

• Cell membranes

• Enzymes

• Immune factors

Amino acids

• 20 amino acids are found in food

• 9 are essential

6. Vitamins

What do vitamins do?

• Help chemical reactions occur

• Some help release energy from carbohydrates, fats, and proteins

• Vitamins do NOT directly provide energy

13 vitamins → 2 groups

Fat-soluble vitamins

A, D, E, K

• Dissolve in fat

• More likely to accumulate in the body

• Greater potential for toxicity

Memory trick: ADEK

Water-soluble vitamins

Vitamin C + B vitamins

• Dissolve in water

• More readily excreted from the body

• More likely to be destroyed by cooking

Example

Vitamin C → helps with collagen synthesis

7. Minerals

Main facts

• Inorganic substances

• Do not contain carbon atoms bound to hydrogen

• Not destroyed by cooking

• Provide no energy

• Needed for normal body functions

Important roles:

• Nervous system

• Skeletal system

• Water balance

Two groups

Major minerals

• Needed in gram amounts

• Examples:

  • Sodium (Na)

  • Potassium (K)

  • Chloride (Cl)

  • Calcium (Ca)

  • Phosphorus (P)

Trace minerals

• Needed in amounts less than 100 mg/day

• Examples:

  • Iron (Fe)

  • Zinc (Zn)

  • Copper (Cu)

  • Selenium (Se)

8. Water

Important facts

• Nutrient needed in the largest quantity

Functions

• Solvent

• Lubricant

• Transports nutrients to cells

• Regulates body temperature

Sources

• Food

• Drinks

• Byproduct of metabolism

9. Phytochemicals & Zoochemicals

These are physiologically active compounds that provide health benefits but are not essential nutrients.

Phytochemicals

Come from plants:

• Fruits

• Vegetables

• Whole grains

• Legumes

Example:

• Glucosinolates in broccoli may help protect against cancer.

Zoochemicals

Come from animals.

Example:

• Lutein and zeaxanthin in eggs may slow macular degeneration.

Important

Multivitamins/mineral supplements contain few or none of these compounds.

Idea: It's better to get nutrients and beneficial compounds from whole foods when possible.

10. Energy

What does the body use energy for?

Energy allows the body to do work, including:

1. Build new compounds

2. Perform muscular movements

3. Promote nerve transmissions

4. Maintain ion balance:

   • Within cells

   • Between cells

   • In blood

Energy is NOT a nutrient

Energy itself is not a nutrient.

11. Calories & Kilocalories

Calorie (cal)

Amount of heat needed to raise the temperature of 1 gram of water by 1°C.

Kilocalorie (kcal)

Amount of heat needed to raise the temperature of 1,000 grams of water by 1°C.

• 1 kcal = 1,000 cal

• Food labels use kilocalories, although they usually just say "Calories."

Energy from macronutrients

12. North American Diet

Acceptable Macronutrient Distribution Ranges (AMDR)

Example from the slide:

• 50% carbohydrates

• 33% fat

• 16% protein

Problems with the North American diet

Common characteristics include:

• Too many calories

• Too much protein from animal sources (60%)

• Too many carbohydrates from simple sugars (50%)

• Too much fat from animal sources/saturated fat

General recommendations

Increase:

• Vitamin A

• Vitamin E

• Potassium

• Iron

• Calcium

• Fruits

• Vegetables

• Whole grains

• Reduced-fat dairy

Decrease/moderate:

• Sodium

• Sugary soft drinks

• Fatty foods

13. What Influences Food Choices?

We eat to satisfy:

• Hunger

• Social needs

• Psychological needs

Hunger

• Physiological/internal need for food

Appetite

• Psychological/external desire to eat

Food choices can be influenced by many factors, including social and psychological factors.

14. Nutritional Health Status

Desirable nutritional status

• Optimal health status

• Nutrients are available in amounts needed for normal body function

Malnutrition

Includes both:

• Undernutrition

• Overnutrition

Undernutrition

• Nutrient intake does not meet the body's needs

• Nutrient stores become depleted

Subclinical deficiency

• Early stage of nutrient deficiency

• Symptoms may not be detectable yet

Overnutrition

• Consuming more nutrients than the body needs

• Most common form in industrialized countries = excess energy intake

• Can lead to obesity

15. Assessing Nutritional Status

Nutrition assessment helps determine nutritional fitness.

6 areas of assessment

1. Anthropometric
Measures body size/composition:

• Height

• Weight

• Skinfold thickness

• Arm muscle circumference

• Body composition

2. Biochemical
Looks at:

• Bloodwork

• Urine

3. Clinical
Physical examination:

• Skin

• Eyes

• Tongue

• Ability to walk

4. Dietary
Looks at:

• Usual food intake

• Food allergies

• Supplements

5. Environmental
Looks at:

• Education

• Economic background

• Marital status

• Number of people in household

• Housing conditions

6. Medical/Familial history
Includes:

• Current/past diseases

• Surgeries

• Weight history

• Medications

• Family medical history

Limitations

Signs/symptoms aren't always specific.

For example:

• Diarrhea

• Skin conditions

• Fatigue

These could have causes unrelated to nutrition.

Also, deficiencies can take years to show their effects.

Example:

• Calcium deficiency during teen years may contribute to osteoporosis later in life.

16. Scientific Research & Nutrition

Why use the scientific method?

The scientific method is a systematic and objective approach used to:

• Discover facts

• Generate knowledge

• Reduce/eliminate errors

Why it matters in nutrition

It helps:

• Create evidence-based dietary guidelines

• Identify relationships between diet and disease

• Replicate and verify findings

• Develop scientific theories/laws

17. Hypothesis

A hypothesis is a proposed explanation that can be tested through research.

James Lind & Scurvy

• Sailors on long voyages often developed scurvy

• James Lind noticed sailors ate fewer fruits and vegetables

• He hypothesized that something missing from their diet caused scurvy

• He tested different substances, including citrus juice

• Citrus prevented/cured scurvy

• We now know vitamin C prevents scurvy

18. Experimental Designs

In vitro

Means "in glass."

• Experiments performed outside a living organism

• Often use cells or parts of living organisms

• Example: test-tube experiments

In vivo

Means "in life."

• Experiments performed on whole living organisms

• Examples:

  • Rats

  • Humans

19. Animal Research

Laboratory animals may be used when a hypothesis cannot ethically or practically be tested on humans.

Before animal studies:

• Researchers need approval from the Institutional Animal Care and Use Committee (IACUC)

Why use animal models?

• Animals can develop conditions that mimic human diseases

• Helps researchers understand:

  • Causes

  • Diagnosis

  • Safety/effects of treatments

20. Human Experimental Research

Human studies investigate health outcomes from dietary practices.

Before a human study:

• Researchers need approval from an Institutional Review Board (IRB).

Gold standard

Randomized controlled trial (RCT)

The slides describe an ideal design as:

• Randomized

• Double-blinded

• Cross-over

• Placebo-controlled

Double-blind

• Neither participants nor researchers know who is in each group.

Cross-over

• Participants receive both treatments being compared, such as treatment and placebo.

Placebo

• A fake treatment that resembles the real treatment.

• Example: sham pill.

21. Epidemiological Studies

Study:

• Occurrence

• Distribution

• Causes of health problems in populations

Case-control study

Compares:

• People with a health condition

• Similar people without the condition

Example:

• People with lung cancer vs. people without lung cancer

Cohort study

• Measures variables in a group of people over time

22. Types of Cohort Studies

Prospective

Think: FORWARD

• Starts with healthy people

• Follows them into the future

• Looks for factors that may contribute to changes in health

Retrospective

Think: BACKWARD

• Looks at people's past exposures

• Used to understand why some people developed a condition and others didn't

Memory trick:
Prospective = forward
Retrospective = backward

23. Correlation

Epidemiological studies can establish correlation.

Correlation

Two variables change during the same period.

Positive/direct correlation

Both variables move in the same direction.

Example:

• As X increases → Y increases

Negative/inverse correlation

Variables move in opposite directions.

Example:

• As X increases → Y decreases

🚨 VERY IMPORTANT:

Correlation does NOT imply causation.

Epidemiological studies cannot establish cause-and-effect relationships by themselves.

Two things may change together because of:

• Coincidence

• Another factor

• A third variable

Spurious correlation

A relationship that appears to exist between two variables but does not represent a true cause-and-effect relationship.

24. Follow-Up Studies

One experiment is NOT enough to accept a hypothesis.

Researchers need:

• More experiments

• Replication

• Consistent results

The more evidence supporting a hypothesis, the more likely it is to be true.

This creates cumulative evidence.

25. Scientific Journals

Scientific journal

A publication containing original scientific articles that are:

• Written by scientists

• Peer-reviewed

• Evaluated by experts in the same field

Why scientific journals matter

They:

• Provide real data

• Use expert peer review

• Improve quality and credibility

• Help inform dietary guidelines

• Help combat misinformation

Examples:

• JAMA

• Nutrition Reviews

• Journal of the Academy of Nutrition and Dietetics

• The BMJ

• British Journal of Nutrition

26. Evaluating Nutrition Claims

When you see a nutrition claim, ask:

🚩 Warning signs

Be cautious if the claim:

• Only discusses advantages

• Claims a new/"secret" breakthrough

• Claims to cure a disease

• Sounds too good to be true

• Is extremely biased against the medical community

• Uses dramatic testimonials

Ask about the research:

• What are the person's scientific credentials?

• How much research exists?

• How large was the study?

• How long did it last?

• What type of study was conducted?

27. Reliable Nutrition Information

Good sources include:

• Scientific books

• Government organizations

• Professional organizations

• Educational organizations

• Consumer organizations

• Scientific journals

• Qualified consultants

Websites

Generally:

• .gov → government

• .edu → educational institutions

• .org → organizations

Be more cautious with:

• .com websites

A website ending doesn't automatically make information true, but it can help you identify the type of source.

28. Dietary Supplements

Examples:

• Vitamins

• Minerals

• Amino acids

• Herbal remedies

Under the Dietary Supplement Health and Education Act (DSHEA) of 1994, these products are classified as foods, not drugs.

Important

Supplements are:

• Less regulated than medications

• Not all thoroughly evaluated by scientists

According to the slides:

• The FDA must generally establish that a product is unsafe to remove it from the market rather than manufacturers having to prove safety before distribution.

29. Being a Savvy Consumer

When buying nutrition-related products:

1. Read and scrutinize labels

2. Look for scientific evidence

3. Don't use products for purposes not listed on the label

4. Be skeptical of exaggerated health claims

5. Look for FDA disclaimers on certain health claims