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

NUTR 2360 — Chapter 2: Tools of a Healthy Diet

1. Planning a Healthy Diet

To plan a healthy diet and reduce disease risk, use:

• Dietary Reference Intakes (DRIs)

• Dietary Guidelines for Americans

• Food labels

• Nutrient databases

• Knowledge of nutrient density and energy density

• Healthy eating principles:

  • Variety

  • Balance

  • Moderation

  • Nutrient density

  • Energy density

2. Dietary Reference Intakes (DRIs)

What are DRIs?

DRIs = recommendations for how much of a nutrient people need for optimal health.

• Set for almost 40 nutrients

• Developed by the Food and Nutrition Board

• Apply to the U.S. and Canada

• Differ based on:

  • Age

  • Gender (after age 9)

  • Pregnancy

• Should be considered using average intake over several days, not just one day.

⭐ 5 DRI standards

1. EAR = Estimated Average Requirement

2. RDA = Recommended Dietary Allowance

3. AI = Adequate Intake

4. UL = Tolerable Upper Intake Level

5. EER = Estimated Energy Requirement

⚠ Also know:

AMDR = Acceptable Macronutrient Distribution Range

It is related to DRIs but is NOT technically a DRI.

3. EAR — Estimated Average Requirement

Definition:

The daily nutrient intake estimated to meet the needs of 50% of healthy people in a specific life-stage group.

• Set for 17 nutrients

• Used mainly for evaluating groups, NOT individuals.

• Requires an accurate way to measure whether the body is functioning properly.

• These measurements are called functional markers.

Example:

If 100 people need a certain amount of Vitamin X:

• EAR meets the needs of about 50 people

• The other 50 may need more.

⭐ Remember:

EAR = 50%

4. RDA — Recommended Dietary Allowance

Definition:

The daily nutrient intake sufficient to meet the needs of 97–98% of healthy individuals.

• Based on the EAR

• Can only be established when an EAR exists

• Generally:

RDA ≈ EAR × 1.2

Important:

RDA is higher than the average person's actual requirement.

If someone regularly consumes less than the RDA, it does not automatically mean they are deficient.

However, regularly consuming below the EAR increases the concern for deficiency.

⭐ Remember:

RDA = 97–98%

5. AI — Adequate Intake

Definition:

A recommended intake used when there is not enough research to establish an EAR/RDA.

Based on observed or experimentally supported estimates of intake needed to maintain good health.

Examples of what researchers may look at:

• Bone health

• Normal body function

Important:

• Intended to cover the needs of about 97–98% of people

• Can be used for individuals

• Used when an EAR cannot be determined

⭐ Remember:

AI = used when there isn't enough evidence to establish an EAR.

6. UL — Tolerable Upper Intake Level

Definition:

The highest daily nutrient intake that is unlikely to cause harmful effects in 97–98% of healthy people.

• Applies to chronic/regular daily intake

• Protects against toxicity

• It is a ceiling, NOT a goal.

⭐ Remember:

UL = don't regularly go above it.

7. EER — Estimated Energy Requirement

Definition:

The average amount of energy/calories needed each day for a specific life-stage group.

EER depends on:

• Age

• Gender

• Height

• Weight

• Physical activity/energy expenditure

Purpose:

Helps promote and maintain a healthy body weight.

Important:

Excess energy can be stored as body fat.

8. DRI Quick Comparison ⭐

Easy memory trick:

EAR → 50%
RDA → 97–98%
UL → Upper limit
EER → Energy

9. How to Use DRIs

DRIs are useful for:

• Planning diets

• Making sure nutrient needs are met

• Evaluating nutrient intake

• Avoiding excessive intake

For diet planning:

✅ Try to meet the RDA or AI
✅ Stay below the UL
❌ Don't intentionally aim for the UL

Important limitation:

DRIs are designed for healthy people.

They are not appropriate for people who are undernourished or have certain diseases/health conditions without appropriate professional guidance.

10. AMDR — Acceptable Macronutrient Distribution Range

AMDR is NOT a DRI.

It gives recommended percentages of calories from:

• Carbohydrates

• Protein

• Fat

Purpose:

Help reduce the risk of nutrition-related chronic diseases.

11. Nutrient Density ⭐

Definition:

Nutrient density = how much nutrition a food provides compared with how much energy (calories) it provides.

A food is nutrient dense when it provides a large amount of nutrients for relatively few calories.

Example:

An orange provides a lot of vitamin C for relatively few calories → nutrient dense.

Calculating Nutrient Density

Step 1:

Calculate the percentage of the nutrient's RDA:

Nutrient in serving ÷ RDA × 100

Step 2:

Calculate the percentage of daily calories:

Calories in serving ÷ EER × 100

Step 3:

Compare the two percentages.

If the % of nutrient needs is greater than the % of calorie needs, the food is nutrient dense.

Example: Orange

• 70 mg vitamin C

• RDA = 65 mg

• 65 calories

• EER = 1,800 calories

Vitamin C:

70 ÷ 65 × 100 = 108%

Calories:

65 ÷ 1,800 × 100 ≈ 4%

So the orange provides about:

• 108% of vitamin C needs

• 4% of calorie needs

➡ Very nutrient dense

12. Energy-Dense / Empty-Calorie Foods

These foods provide lots of calories but relatively few nutrients.

Usually high in:

• Sugar

• Fat

Examples:

• Sugared soft drinks

• Chips

• Cookies

• Candy

⭐ Difference:

Nutrient dense → lots of nutrients, relatively few calories

Energy dense → lots of calories, relatively few nutrients

13. Daily Values (DVs)

What are DVs?

Daily Values are general standards developed by the FDA for food labels.

They are found on the Nutrition Facts label.

DVs vs DRIs

DRIs:

• More specific

• Depend on age, gender, pregnancy, etc.

DVs:

• General standards

• Designed to be practical for food labels

• Usually apply to people over age 4

⭐ Important:

The Daily Values on most food labels are for people over 4 years old.

Exceptions:

• Infants

• Toddlers

• Pregnant/lactating women

when the product is specifically marketed for those groups.

14. RDI — Reference Daily Intake

RDI = standards used for vitamins and most minerals on food labels.

For people over age 4, the RDI generally uses the highest value needed among different life-stage groups.

Example:

If adolescent females and adult women have the highest iron requirement of 18 mg/day, the RDI for iron may be based on that value.

15. DRV — Daily Reference Value

DRVs are standards used for:

Energy-producing nutrients:

• Fat

• Saturated fat

• Carbohydrates

• Protein

• Fiber

Also:

• Cholesterol

• Sodium

Important:

For energy-producing nutrients, the FDA uses 2,000 calories/day as the reference amount for calculating %DV.

⭐ Remember:

RDI → vitamins + most minerals

DRV → fat, carbs, protein, fiber, etc.

16. Nutrition Facts Labels

Food labels provide information about:

• Product name

• Manufacturer

• Amount of food in package

• Ingredients

• Allergens

• Nutrition Facts

Ingredients list:

Ingredients are listed in descending order by weight.

➡ The ingredient present in the greatest amount is listed first.

17. Nutrition Facts Panel

The Nutrition Facts panel gives nutrient information based on a serving size.

Serving sizes are:

• Specified by the FDA

• Based on typical amounts Americans eat

Nutrients commonly required on labels:

• Calories

• Total fat

• Saturated fat

• Trans fat

• Cholesterol

• Sodium

• Total carbohydrates

• Fiber

• Total sugars

• Added sugars

• Protein

• Vitamin D

• Calcium

• Iron

• Potassium

⚠ Protein:

For foods intended for people over age 4, listing the %DV for protein is not mandatory because protein deficiency is not considered a major public health concern in the U.S.

18. Nutrients Americans Often Get Too Much/Little Of

Many people get TOO MUCH:

• Fat

• Saturated fat

• Trans fat

• Cholesterol

• Sodium

• Sugar

Many people DON'T GET ENOUGH:

• Fiber

• Calcium

• Iron

• Potassium

• Vitamin D

⭐ This explains why many of these nutrients appear prominently on Nutrition Facts labels.

19. Claims on Food Labels

Food package claims must follow FDA regulations.

There are 3 major types:

1. Nutrient content claims

2. Health claims

3. Structure/function claims

Nutrient Content Claims

Describe the amount or level of a nutrient in a food.

Examples include claims such as:

• Low fat

• High calcium

• Good source of fiber

➡ FDA regulates/approves these claims.

Health Claims

Describe a relationship between:

A food/nutrient ↔ a disease or health condition

Health claims must meet FDA requirements.

They must have significant scientific agreement supporting them.

⭐ Remember:

Health claim = food/nutrient + disease relationship

Structure/Function Claims

Describe how a nutrient affects the:

• Structure of the body

• Function of the body

Important:

The FDA does not approve or authorize these claims in the same way it approves health claims.

The manufacturer is responsible for making sure the claim is accurate and not misleading.

⭐ Easy difference:

Health claim → disease

Structure/function → body function/structure

20. Nutrient Databases

Nutrient databases allow us to:

• Estimate calories in foods

• Estimate nutrient amounts

• Compare intake with dietary recommendations

Limitations:

They cannot fully account for:

• Factors that change nutrient levels in foods

• How nutrients are absorbed and used by the body

➡ Database values are estimates, not always exact amounts.

21. Dietary Guidelines for Americans (DGA)

The Dietary Guidelines for Americans are the U.S. government's foundation for:

• Nutrition policy

• Nutrition education

• Healthy eating recommendations

Developed by:

• USDA

• DHHS (Department of Health and Human Services)

They are based on current scientific evidence about:

• Nutrition

• Physical activity

• Healthy lifestyle choices

22. Goals of the Dietary Guidelines

The guidelines aim to meet nutrient needs while reducing risk of:

• Obesity

• Hypertension

• Cardiovascular disease

• Type 2 diabetes

• Osteoporosis

• Alcohol-related problems

• Foodborne illness

⭐ Main idea:

Nutrient needs should be met primarily through food.

23. 2025–2030 Dietary Guidelines

Your slides say the 2025–2030 Dietary Guidelines emphasize:

• Eat the right amount for you

• Prioritize protein foods at meals

• Consume dairy

• Eat vegetables and fruits throughout the day

• Include healthy fats

• Focus on whole grains

• Limit highly processed foods

• Limit added sugars

• Limit refined carbohydrates

• Limit alcoholic beverages

⭐ Main theme:

Choose nutrient-dense foods and limit foods that provide lots of calories with fewer beneficial nutrients.

24. MyPlate / Food Pyramid

Historical progression:

1947 → 7 food groups

⬇

1992 → Food Guide Pyramid

⬇

2005 → MyPyramid

⬇

2011–2025 → MyPlate

⬇

2025–2030 → New Food Pyramid

MyPlate:

Previously emphasized 5 food groups:

• Fruits

• Vegetables

• Grains

• Protein

• Dairy

Its purpose was to help people visualize what a healthy plate could look like.

Important for your class: Your slides specifically state that MyPlate was discontinued as of 2026 and the 2025–2030 guidelines use a Food Pyramid instead.

25. Concerns About the New Guidelines

The Academy of Nutrition and Dietetics supports:

• Nutrient-dense foods

• Fruits and vegetables

• Whole grains

• Limiting highly processed foods

• Limiting added sugars

• Keeping saturated fat below 10% of total calories

• Prioritizing healthier fats

• More attention to fiber and microbiome health

Concerns raised by the Academy:

• Emphasis on butter, beef tallow, red meat, and full-fat dairy

• Lack of consideration for people who don't consume dairy

• Recommendations concerning low-calorie non-nutritive sweeteners

• Synthetic food dyes and the need for more research

⭐ For your test:

Know that these are concerns expressed by the Academy, not necessarily facts that the entire nutrition field agrees upon.

26. Putting Dietary Guidelines Into Action

A healthy eating plan should:

1. Consider your current health

Think about:

• Current health

• Family history

2. Identify changes

Figure out what parts of your diet need improvement.

3. Make a plan

Choose realistic changes you can incorporate.

4. Evaluate

See whether the changes are actually helping.

NUTR 2360 — Chapter 4: Human Digestion and Absorption

1. Organization of the Human Body

The body is organized from smallest to largest:

Cells → Tissues → Organs → Organ Systems

Cells

The cell is the smallest functional unit of the body.

Cells can:

• Grow

• Absorb nutrients

• Use energy

• Perform metabolic/physiological functions

• Remove waste

Cells need:

• Energy → carbohydrates, proteins, lipids → converted into ATP

• Water

• Building materials → such as amino acids

• Chemical regulators → such as vitamins

⭐ ATP

ATP (adenosine triphosphate) = usable energy for cells.

2. Four Types of Human Tissue

⭐ Remember:

Tissues combine to form organs.

3. Digestive Organ System

The digestive system:

• Digests food

• Absorbs nutrients

• Removes waste

• Makes nutrients available for cells

• Helps regulate the body

• Helps with immune function

• Houses beneficial bacteria called microbiota

Major organs of the GI tract:

1. Mouth

2. Esophagus

3. Stomach

4. Small intestine

5. Large intestine

6. Anus

Accessory organs:

• Liver

• Gallbladder

• Pancreas

⭐ Important:

Accessory organs help digestion but food does NOT pass through them.

4. Sphincters

Sphincters = ring-like muscles that open and close to control movement through the GI tract.

They prevent contents from moving the wrong direction.

⭐ Know where the major sphincters are located.

Important ones include:

• Lower esophageal sphincter (LES) → between esophagus and stomach

• Pyloric sphincter → between stomach and small intestine

• Sphincter of Oddi → controls bile/pancreatic secretions entering the duodenum

5. GI Motility

GI motility = coordinated contraction and relaxation that moves and mixes food through the digestive tract.

Peristalsis

• Wave-like contractions

• Pushes food forward

• Helps move food through the GI tract

Think:

Peristalsis = propulsion

Segmentation

• Back-and-forth contractions

• Breaks up and mixes food

• Occurs mainly in the small intestine

• Helps nutrients contact the intestinal wall

Think:

Segmentation = mixing

Mass Movements

• Large areas of the intestine contract at once

• Occur in the large intestine

• Move feces toward the rectum

Normal transit time:

A meal typically takes about 24–60 hours to travel through the GI tract.

6. Digestive Enzymes

Digestive enzymes = proteins that speed up digestion.

They break large food molecules into smaller molecules that can be absorbed.

They work through:

Hydrolysis

Hydrolysis uses water to break chemical bonds.

Enzymes act on:

• Carbohydrates

• Proteins

• Fats

Produced by:

• Salivary glands

• Stomach

• Pancreas

• Small intestine

⭐ Most digestive enzymes are produced by the pancreas.

7. What Happens if You Don't Produce Enough Enzymes?

Insufficient enzyme production can cause:

Incomplete digestion → undigested food reaches large intestine → bacteria break it down → gases/acids → bloating and abdominal distention

It can also cause limited nutrient absorption.

This can happen when the:

• Small intestine is diseased

• Pancreas is diseased

• Person is malnourished

👄 8. Digestion Begins in the Mouth

Teeth

• Tear and grind food

• Chewing increases surface area

• More surface area = enzymes can work more effectively

Saliva

Food mixes with saliva and forms a bolus.

Bolus = chewed food mixed with saliva.

9. Saliva

Salivary glands produce about 1 liter (4 cups) of saliva per day.

Important components:

Lysozyme

• Helps destroy bacteria

Mucus

• Lubricates food

• Holds the bolus together

Amylase

• Begins digestion of starch

• Breaks starch into smaller sugars

Lipase

• Begins fat digestion

⭐ Remember:

Amylase → carbohydrates/starch

Lipase → fat

10. Esophagus

The esophagus is a muscular tube connecting the:

Pharynx → stomach

Swallowing

Moves the bolus from the mouth into the esophagus.

Epiglottis

A flap that helps prevent food from entering the:

Trachea (windpipe)

Instead, food is directed toward the esophagus.

🥣 11. Stomach

The stomach acts like a mixing tank.

Food enters through the:

Lower esophageal sphincter (LES)

LES problem:

If the LES doesn't work properly → stomach contents can move upward → heartburn/reflux

Stomach functions:

• Stores food

• Mixes food with gastric secretions

• Begins significant protein digestion

• Produces substances needed for digestion

Limited absorption occurs here:

The stomach can absorb:

• Water

• Some fat

• About 20% of alcohol

12. Gastric Juice

The stomach produces about 8 cups of gastric juice per day.

Gastric juice contains:

Hydrochloric acid (HCl)

• Helps destroy bacteria and viruses

• Helps dissolve minerals

• Denatures/inactivates proteins

• Activates pepsinogen into pepsin

Intrinsic factor

• Produced by parietal cells

• Important for vitamin B12 absorption later in the small intestine

Pepsinogen

• Inactive protein-digesting enzyme

• Produced by chief cells

• Activated into pepsin

Gastric lipase

• Helps digest fat

13. Protein Digestion in the Stomach ⭐

Know this sequence:

Gastrin → HCl + pepsinogen released

⬇

HCl converts pepsinogen → pepsin

⬇

Pepsin breaks proteins → peptides

⭐ Pepsin = protein digestion

14. Gastrin

Gastrin = hormone produced in the stomach.

It:

• Stimulates release of HCl

• Stimulates release of pepsinogen

• Stimulates stomach motility

Gastrin levels are highest at the beginning of a meal and decrease as the meal continues.

15. Ghrelin

Ghrelin = hormone that increases appetite and food intake.

⭐ Remember:

Ghrelin → hunger/appetite increases

16. Stomach Protection

The stomach produces mucus.

Mucus:

• Lubricates the stomach

• Protects the stomach lining from HCl and pepsin

Prostaglandins

Help support mucus production.

NSAIDs

Examples include aspirin and other nonsteroidal anti-inflammatory drugs.

They can reduce prostaglandin production.

⬇

Less mucus protection

⬇

Stomach lining becomes more vulnerable to acid damage.

17. Chyme

When food enters the stomach, it mixes with stomach secretions.

Bolus → stomach → mixed with gastric secretions → chyme

Chyme:

Partially digested, acidic food mixture.

It leaves the stomach through the:

Pyloric sphincter → small intestine

Timing:

It generally takes about 1–4 hours for stomach contents to move into the small intestine.

18. Small Intestine ⭐⭐⭐

The small intestine is the major site of digestion and absorption.

About 95% of food energy is digested/absorbed here.

Three sections:

1. Duodenum

2. Jejunum

3. Ileum

Easy memory trick:

DJI

Duodenum
Jejunum
Ileum

19. What Does the Small Intestine Absorb?

The small intestine absorbs:

• Glucose

• Amino acids

• Fat

• Vitamins

• Minerals

• Water

• Alcohol

⭐ Major takeaway:

Most nutrient absorption happens in the small intestine.

20. Villi and Microvilli ⭐

The small intestine has structures that greatly increase surface area.

Villi

Finger-like projections lining the small intestine.

Microvilli

Tiny projections on the surface of intestinal cells.

Together they create a huge surface area for absorption.

Enterocytes

Enterocytes = intestinal cells that absorb nutrients.

They have a brush border containing microvilli.

The brush border also contains enzymes.

Why is surface area important?

More surface area → more contact with nutrients → more efficient absorption

21. Segmentation Helps Absorption

Segmentation:

• Mixes chyme

• Moves chyme back and forth

• Slows its movement

• Brings nutrients into contact with the villi

➡ This helps absorption.

🟢 22. Liver + Gallbladder + Bile

Liver

Produces bile

Gallbladder

Stores bile

Bile

Helps with fat digestion and absorption.

It emulsifies fat.

Emulsification:

Breaks large fat globules into much smaller droplets, making fat easier to digest and absorb.

⭐ Remember:

Liver = makes bile

Gallbladder = stores bile

Bile = helps digest/absorb fat

23. Enterohepatic Circulation

Bile is recycled.

Bile → small intestine → reabsorbed in ileum → returned to liver

A small amount that isn't reabsorbed leaves the body in feces.

⭐ Important:

Ileum = major site of bile reabsorption

24. Pancreas

The pancreas produces pancreatic juice.

It contains:

Sodium bicarbonate

• Neutralizes acidic chyme coming from the stomach

Pancreatic amylase

• Digests starch/carbohydrates

Pancreatic lipase

• Digests fat

Proteases

• Digest proteins

25. Sphincter of Oddi

The:

Bile duct + pancreatic duct

come together and empty into the:

Duodenum

The sphincter of Oddi controls this release.

⭐ Know:

Sphincter of Oddi → duodenum

26. Digestive Hormones ⭐⭐⭐

This table is VERY test-worthy:

27. The Big 3 Hormones to Know ⭐⭐⭐

If you don't have time to memorize everything, focus on:

Gastrin

Food in stomach → HCl + pepsinogen

CCK

Fat → pancreatic enzymes + bile

Secretin

Acidic chyme → bicarbonate

Easy memory trick:

CCK = fat → enzymes + bile

Secretin = acid → bicarbonate

28. Nutrient Absorption

After digestion, nutrients must cross the intestinal wall and enter the body.

There are 4 major absorption methods:

1. Passive diffusion

2. Facilitated diffusion

3. Active transport

4. Endocytosis

29. Passive Diffusion

Nutrients move:

High concentration → low concentration

No energy required.

Examples:

• Fats

• Water

• Some minerals

⭐ Think:

Passive = naturally moves down the concentration gradient

30. Facilitated Diffusion

Nutrients move:

High concentration → low concentration

BUT they need a carrier protein to cross the membrane.

Example:

• Fructose

⭐ Difference:

Passive diffusion = no carrier

Facilitated diffusion = carrier protein

Both move high → low.

31. Active Transport

Nutrients move:

Low concentration → high concentration

This requires:

• Energy

• Carrier proteins

Examples:

• Glucose

• Amino acids

⭐ Remember:

Active = energy required

32. Endocytosis

The cell engulfs a substance and forms a vesicle around it.

Think:

Cell membrane surrounds nutrient → brings it into cell

33. Absorption Isn't Only in the Small Intestine

The small intestine is the major site, but it is NOT the only place where absorption occurs.

For example, the stomach can absorb:

• Water

• Some fat

• Some alcohol

The large intestine also absorbs certain substances, especially:

• Water

• Some electrolytes