Chapter 1: The Science of Nutrition

Nutrition Overview

Nutrition is the science of food; the nutrients and the substances therein; their action, interaction, and balance in relation to health and disease; and the process by which the organism ingests, digests, absorbs, transports, utilizes, and excretes food substances.
This chapter outlines key terms, energy-yielding and non-energy-yielding nutrients, dietary patterns, factors influencing food choices, nutritional status, genetics, and the scientific method used in nutrition research.

Nutrients: Essentials and Functional Categories

Nutrients are substances essential for health that the body cannot make or makes in quantities too small to support life.
Essential nutrient criteria:
- Has a specific biological function.
- Absence from the diet leads to decline in biological function.
- Adding the missing substance back to the diet before permanent damage occurs restores normal biological function.
Functional categories of nutrients (with some overlap):
- Primarily provide energy
- Important for growth and development
- Help keep body functions running smoothly

Energy-Yielding vs Non-Energy-Yielding Nutrients

Energy-yielding nutrients provide usable energy for body functions and activities:
- Carbohydrate
- Lipids (fats and oils)
- Protein (amino acids)
- Alcohol (non-nutrient)
Non-energy-yielding nutrients include vitamins, minerals, and water.
Physiological fuel values (energy values per gram):
- Carbohydrate: 4 ext{kcal/g}
- Protein: 4 ext{kcal/g}
- Fat: 9 ext{kcal/g}
- Alcohol: 7 ext{kcal/g}
Note on calories vs kilocalories: 1 kilocalorie (kcal) is the amount of heat energy needed to raise the temperature of 1 kg of water by 1°C. In nutrition, the term "calorie" on food labels typically refers to kilocalories. 1 ext{kcal} = 1000 ext{ cal}
Example energy calculations (illustrative):
- Hamburger: Carbohydrate 39 g, Fat 32 g, Protein 30 g
- 39 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 156 ext{ kcal}
- 32 ext{ g} imes 9rac{ ext{kcal}}{ ext{g}} = 288 ext{ kcal}
- 30 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 120 ext{ kcal}
- Total (rounded): 564 ext{ kcal}
- 8-ounce Piña Colada: Carbohydrate 57 g, Fat 5 g, Protein 1 g, Alcohol 23 g
- 57 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 228 ext{ kcal}
- 5 ext{ g} imes 9rac{ ext{kcal}}{ ext{g}} = 45 ext{ kcal}
- 1 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 4 ext{ kcal}
- 23 ext{ g} imes 7rac{ ext{kcal}}{ ext{g}} = 161 ext{ kcal}
- Total: 438 ext{ kcal}
- Note: The slide shows a calculation that appears to misstate one value (57 g carbs × 4 kcal/g = 288 kcal); the correct calculation is 57 × 4 = 228 kcal. The total above uses the correct arithmetic.

The North American Diet

Energy distribution (typical):
- Protein: 16 ext{ %} of energy
- Carbohydrates: 50 ext{ %} of energy
- Fat: 33 ext{ %} of energy
Issues observed:
- Too many total calories
- Too much protein from animal sources; too little from plants
- Too many simple carbohydrates; too few complex carbohydrates
- Too much fat from animal sources; too little from plant sources
Improvement strategies mentioned:
- Increase intake of foods rich in vitamins A and E, iron, and calcium
- Decrease sodium intake
- Moderate intake of sugary soft drinks and fatty foods
- Eat more fruits, vegetables, whole-grain breads, and reduced-fat dairy

What Influences Our Food Choices?

Daily food intake is a mix of hunger and social/psychological needs.
Hunger: physical need for food.
Appetite: psychological desire to eat.
Food choices depend on many factors, including:
- Food flavor, texture, and appearance preferences
- Food availability
- Food marketing and influencers
- Health and nutrition concerns, knowledge, and beliefs
- Social needs and network of family and friends
- Routines and habits; lifestyle and beliefs
- Food cost and education/occupation/income
- Food customs and culture
- Education, occupation, and income

Nutritional Status and Assessment

Nutritional status describes whether the body has enough nutrients to support normal functions and stores.
Desirable (optimal) status vs malnutrition:
- Undernutrition: nutrient intake does not meet needs; stores depleted; subclinical stage possible
- Overnutrition: consumption of more nutrients than needed; most common form in industrialized nations is excess energy intake
Components of nutritional assessment:
- Family history and personal history (self history)
- Anthropometric assessment (height, weight, skinfolds, limb measurements, body composition)
- Biochemical (laboratory) assessment (blood/urine compounds)
- Clinical assessment (physical signs, observations)
- Dietary assessment (usual intake, allergies, supplements)
- Environmental assessment (education, economic background, housing)
Iron status as an example of assessment stages: undernutrition leads to reduced iron in blood and fatigue; adequate stores; excessive stores can damage liver

Health Objectives: Healthy People 2030

Healthy People is a national, science-based framework with 10-year goals to improve health across the population.
Focus areas include nutrition and weight status objectives (Table 1-5 in the text).

Nutritional Status and Disease Risk: Genetics and Nutrition

Our genes influence how we respond to nutrients; DNA directs how nutrients are transformed and used in the body.
Individual genetic risks contribute to nutrition-related diseases; mutations may increase disease risk.
Family history is a major risk factor for diseases such as diabetes, various cancers, osteoporosis, cardiovascular disease, hypertension, and obesity.
Heredity is not destiny: lifestyle can influence gene expression and disease onset (e.g., nutritious diet, regular exercise, weight control, medical treatment).
Your genetic profile can be explored through family history or genetic testing, which has limitations (not all risks identifiable; susceptibility does not guarantee disease; no cure via genetics alone).
Gene therapy (conceptual steps): normal DNA isolation → packaging into a delivery vehicle (virus) → delivery to affected cells → normal genetic function; not FDA-approved yet.
Family tree examples and risk visualization: a provided example shows multiple relatives with diseases such as stroke, colon cancer, prostate cancer, alcoholism, etc., illustrating how family history can imply risk.

Genetic Testing and Counseling

Genetic testing analyzes genes to estimate disease likelihood.
Benefits include proactive health planning and informed risk assessment.
Limitations:
- Not all risks can be identified
- Susceptibility does not guarantee disease
- No cure for genetic alterations; treatment focuses on health management
Genetic counseling recommended to interpret results and guide decisions.

The Scientific Method in Nutrition Research

The scientific method is used to uncover facts and minimize errors through controlled experiments testing hypotheses.
Key requirements: open, curious, skeptical mindset; objectivity; reproducibility.
Typical steps:
1) Observations and questions
2) Hypothesis generation
3) Conduct research experiments
4) Findings evaluated by peers and published
5) Follow-up experiments to confirm or extend findings
6) Acceptance or rejection of the hypothesis based on accumulated evidence
Example (hypothesis evolution about low-calorie high-protein vs low-calorie high-carbohydrate diets):
- Early observations suggested faster weight loss on low-calorie/high-protein diets
- Multiple studies over years showed no consistent long-term difference in weight loss between the two approaches
- Conclusions evolved with follow-up studies and broader evidence, illustrating the need for continued replication and review

Research Designs and Evidence in Nutrition

Laboratory animal experiments: used when human testing is not feasible; chosen animal models must be relevant.
Human experiments require ethical oversight and informed consent; designs include:
- Migrant studies (history-laden cohort-like designs)
- Cohort studies
- Case-control studies
- Double-blind, placebo-controlled trials (with single- or double-blind designs)
Case-Control studies: compare individuals with a condition (cases) to those without (controls); matched by age, race, gender; limitation: cannot prove causation.
Blinded studies: reduce bias; double-blind where neither participants nor researchers know group assignments.
Peer review: essential step before publication; examples include major journals in nutrition and medicine.
Follow-up studies: replication and confirmation strengthen confidence in findings.
Systematic reviews: critical synthesis of studies on a topic; organizations include the Evidence Analysis Library (EAL), USDA Nutrition Evidence Library, eLENA, and Cochrane Collaboration.

Evaluating Nutrition Claims and Supplements

Practical guidelines to evaluate nutrition claims:
1) Apply basic nutrition principles.
2) Be wary of claims that only list advantages, promise cures, or sound too good to be true; beware extreme bias against conventional medicine.
3) Check the scientific credentials of the claimant.
4) Consider the research behind the claims: study size, duration, and study type.
5) Be cautious of hype and press conferences.
Buying nutrition-related products (DSHEA):
- The Dietary Supplement Health and Education Act of 1994 classifies vitamins, minerals, amino acids, and herbal remedies as "foods." FDA must prove unsafe products to ban them; products labeled as dietary supplements can be marketed without FDA pre-approval.
- Health-protective practices when evaluating supplements:
- Scrutinize labels and ensure there is scientific support for claims
- Do not use products beyond labeled indications
- Labels may claim general well-being, how a product provides benefit, or how it affects bodily structure or function

Phytochemicals, Zoochemicals, and Functional Foods

Phytochemicals: physiologically active compounds in plants that may provide health benefits; not essential nutrients.
Zoochemicals: physiologically active compounds in animal-origin foods that may provide health benefits; not essential nutrients.
Functional foods: foods rich in phytochemicals/zoochemicals that provide health benefits beyond traditional nutrient content.
- Categories include conventional foods (unmodified), modified/fortified/enhanced foods, medical foods (supervised), and special dietary use foods.

Phytochemicals Under Study (selected examples)

Allyl sulfides/organosulfides (garlic, onions, leeks)
Saponins (garlic, onions, licorice, legumes)
Carotenoids (e.g., lycopene) in colorful fruits/vegetables and egg yolks
Monoterpenes (citrus fruits)
Capsaicin (chili peppers)
Lignans (flaxseed, berries, whole grains)
Indoles (cruciferous vegetables: broccoli, cabbage, kale)
Isothiocyanates (cruciferous vegetables, especially broccoli)
Phytosterols (soybeans, other legumes, cucumbers, other fruits/vegetables)
Flavonoids (citrus, onions, apples, grapes, red wine, tea, chocolate, tomatoes)
Isoflavones (soybeans, fava beans, other legumes)
Catechins (tea)
Ellagic acid (strawberries, raspberries, grapes, apples, bananas, nuts)
Anthocyanosides (red, blue, purple produce)
Fructooligosaccharides (onions, bananas, oranges)
Stilbenoids (e.g., resveratrol in blueberries, grapes, peanuts, red wine)

Zoochemicals Under Study

Sphingolipids (meat, dairy products)
Conjugated linoleic acid (meat, cheese)

Functional Foods: Categories and Examples

Conventional foods: unmodified whole foods (e.g., apples, broccoli)
Modified foods: fortified, enriched, or enhanced for added benefits (e.g., fortified cereals)
Medical foods: designed to manage specific health conditions under medical supervision
Special dietary use foods: meet particular dietary needs

Fermented Foods

Fermentation relies on bacteria, yeast, or fungi to convert sugars/starches to acids for preservation
May provide probiotic benefits; common example: yogurt

Energy Sources and Uses

Energy is required for body functions and work; sourced from carbohydrates, proteins, fats, and alcohol (non-nutrients)
Measured in kilocalories (Calories)
Energy enables building compounds, moving muscles, transmitting nerve impulses, balancing cellular ions

Calorie, Calorie Counting, and Nutrition Labels

A slice of bread example (Nutrition Facts panel) illustrates:
- Serving size, calories per serving, fat, saturated fat, trans fat, cholesterol, sodium, total carbohydrate, dietary fiber, total sugars, added sugars (if present), protein, vitamins/minerals
Calorie approximations are used to estimate energy intake and guide dietary planning

The Leading Causes of Death in the U.S. (Overview)

Heart disease and cancer are the top two causes, with cardiovascular disease being a broad category including heart disease and stroke
Other major causes include chronic obstructive pulmonary disease (COPD), accidents, diabetes, influenza/pneumonia, Alzheimer disease, kidney disease, suicide, and all other causes
Exact numerical percentages in the slide deck (for reference):
- Heart disease: 23 ext{%}
- Cancer: 21 ext{%}
- Cerebrovascular disease (stroke): 5 ext{%}
- COPD: 6 ext{%}
- Accidents/adverse effects: 6 ext{%}
- Diabetes: 3 ext{%}
- Influenza/pneumonia: 2 ext{%}
- Alzheimer disease: 4 ext{%}
- Kidney disease: 2 ext{%}
- Suicide: 2 ext{%}
- All other causes: 24 ext{%}

Assessing Nutritional Status: Practical Notes

A nutritional assessment can help determine nutritional fitness and guide interventions.
It should include: family history, anthropometric data, biochemical markers, clinical signs, dietary intake, and environmental context.

The Nutrition Care Process (NCP)

A registered dietitian nutritionist (RDN) follows the NCP:
- Conduct a nutrition assessment
- Diagnose nutrition-related problems
- Develop an intervention plan
- Monitor and evaluate progress

Genetics and Nutrition: How Genes Influence Nutrition-Related Health

Genes influence how the body processes nutrients; DNA directs how nutrients are transformed and assembled into body structures and compounds.
Individual genetic risks are important in determining disease development; a mutation is a change in DNA sequence that can increase disease risk.
Family history is a key risk factor for nutrition-related diseases (diabetes, cancer, osteoporosis, CVD, hypertension, obesity).
Heredity is not destiny; lifestyle choices can modulate gene expression and disease onset (e.g., nutritious diet, exercise, weight management, medical care).
Your genetic profile can be explored via family history and genetic testing; tests have limitations and are not determinative of disease.

Gene Therapy and Genetic Testing

Gene therapy concept: replace faulty genetic material to restore function; not yet FDA-approved.
Genetic testing: helps assess risk, often with a genetic counselor; limitations include incomplete risk prediction and no guaranteed prevention or cure.
Family trees illustrating multi-generational risk can aid in understanding inherited risk and inform screening strategies.

The Scientific Research Process: How We Build Nutrition Knowledge

The scientific method relies on observations, hypotheses, controlled experiments, and peer review.
Evidence accumulates through multiple studies and follow-up experiments; one study is rarely enough to prove a hypothesis.
Data synthesis through systematic reviews helps establish whether a hypothesis is supported by a body of evidence.

Evaluating Nutrition Claims and Products: Key Takeaways

Apply core nutrition knowledge to assess claims.
Be cautious of sensational or one-sided claims; beware of cures or extreme biases.
Check the credentials of the source and the type, size, and duration of the supporting studies.
Be wary of hype, press briefings, and marketing spin.
Dietary supplements are regulated under DSHEA (1994): not required to prove safety/efficacy before marketing; FDA intervention occurs after safety concerns arise; labels may claim general well-being or functional effects but cannot claim disease cure without approval.

Additional Notes: Text-Alternative Summaries (for Accessibility)

Leading causes of death, carbohydrate/lipid/protein visuals, and other content include text-based summaries that mirror the slide content for accessibility.
Examples include the breakdown of carbohydrates into simple and complex forms, and the life-cycle view of fats, proteins, and carbohydrates in foods.
For quick reference, key energy values to remember: ext{Carbohydrate} = 4 ext{kcal/g}, ext{ Protein} = 4 ext{kcal/g}, ext{ Fat} = 9 ext{kcal/g}, ext{ Alcohol} = 7 ext{kcal/g}
An end-to-end example of energy calculation using a food item can be reproduced using the general formulas above, with the total energy equal to the sum of each macronutrient contribution.
Important conceptual distinctions to internalize:
- Distinguish energy-yielding vs non-energy-yielding nutrients.
- Distinguish essential vs non-essential nutrients.
- Understand how dietary patterns influence health outcomes and disease risk.

Quick Reference: Key Formulas and Values (LaTeX)

Nutrient energy values:
ext{Carbohydrate} = 4rac{ ext{kcal}}{ ext{g}},
ewline ext{Protein} = 4rac{ ext{kcal}}{ ext{g}},
ewline ext{Fat} = 9rac{ ext{kcal}}{ ext{g}},
ewline ext{Alcohol} = 7rac{ ext{kcal}}{ ext{g}}
Example energy calculation (correct arithmetic):
- 39 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 156 ext{ kcal}
- 32 ext{ g} imes 9rac{ ext{kcal}}{ ext{g}} = 288 ext{ kcal}
- 30 ext{ g} imes 4rac{ ext{kcal}}{ ext{g}} = 120 ext{ kcal}
- Total: 564 ext{ kcal}
Calorie vs kilocalorie:
1 ext{kcal} = 1000 ext{ cal}