Chapter 1 — Food Choices & Human Health

Definitions and Core Concepts

Nutrition

• Study of the nutrients and other biologically–active compounds in both food and the human body.
• Extends to human behaviours related to food (e.g., purchasing, preparation, cultural practices).
• Significance: Serves as the scientific foundation for dietary guidelines, health‐promotion policies, and personalized nutrition advice.

Diet & Food

• Diet: The habitual pattern of foods and beverages consumed by an individual or population.
  • Dynamic—changes across life-stage, culture, and environment.
• Food: Any substance the body can ingest and assimilate to sustain life and health.
  • Primary carrier of nutrients (macro, micro, phyto-, and zoo-chemicals).
• Practical implication: Evaluating diet quality requires looking at long-term patterns, not isolated meals.

Health

• Defined as optimal physiological functioning without evidence of disease or abnormality.
• Public-health viewpoint (Health Canada): Achieving optimal health in Canadians demands stronger emphasis on health promotion, illness prevention, and integration of nutrition into all such efforts.
• Ethical stance: Equity in access to nutritious foods is a social determinant of health and a public responsibility.

Role of Nutrition in Disease Prevention

• Diet is a modifiable risk factor for many chronic illnesses (CVD, type 2 diabetes, certain cancers, osteoporosis, dental caries).
• Genetics also plays a major role; the interaction of diet and gene variants can amplify or mitigate disease risk.
• Nutritional Genomics = Study of how:
  • Nutrients influence gene expression (nutrigenomics).
  • Genetic variability alters individual responses to nutrients (nutrigenetics).
• Real-world relevance: Explains why one person’s high-sodium intake elevates blood pressure dramatically while another’s does not.
• Ethical implication: Precision nutrition must avoid genetic discrimination and ensure privacy.

Classes of Nutrients

• Nutrients are indispensable for energy, growth, body structure, and physiological regulation.

Energy-Providing Nutrients

• Carbohydrates, fats (lipids), proteins.

Other Nutrients

• Water, vitamins, minerals (no caloric value but essential for metabolism, structure, fluid balance).

Essential Nutrients

• Cannot be synthesized by the body in sufficient quantities; must come from food.
• Two categories:
  1. Fully essential—body makes none (e.g., vitamin C in humans).
  2. Conditionally essential—body normally synthesizes but fails under specific conditions (e.g., histidine during growth, certain trauma or disease states).

Essential Amino Acids – mnemonic “TV TILL PM”

• Threonine
• Valine
• Tryptophan
• Isoleucine
• Leucine
• Lysine
• Phenylalanine
• Methionine

Essential Fatty Acids (EFAs)

• Linoleic acid (omega-6)
• Linolenic acid (alpha-linolenic, omega-3)

Vitamins

• Fat-soluble: A, D, E; vitamin K is considered conditional due to gut synthesis variability.
• Water-soluble: All B-complex vitamins plus vitamin C.

Minerals

• All dietary minerals are essential; include macro- (Ca, P, Mg, Na, K, Cl, S) and micro- (Fe, Zn, Cu, Se, I, Mn, Cr, Mo, Co) elements.

Energy Values and Calculations

• Energy (calorie) values of macronutrients:
  • Carbohydrate: 4\;\text{kcal\,g}^{-1}
  • Protein: 4\;\text{kcal\,g}^{-1}
  • Fat (lipid): 9\;\text{kcal\,g}^{-1}
  • Alcohol: 7\;\text{kcal\,g}^{-1} (provides energy but not a nutrient)
• Food mass is measured in grams (g); energy usually expressed in kilocalories (kcal) or Calories (uppercase C = kcal).

Worked Examples

Example 1 – % Calories from Macronutrients (Crispers®)

• Nutrient content (per 25\,\text{g}): 1.4\,\text{g} protein, 5.5\,\text{g} fat, 17\,\text{g} CHO, total 123\,\text{kcal}.
• Calories from fat = 5.5\times9 = 49.5\,\text{kcal} → %fat Calories = (49.5/123)\times100 \approx 40\%.
• Calories from CHO = 17\times4 = 68\,\text{kcal} → %CHO Calories = \approx 55\%.
• Remaining \approx5\% from protein.

Example 2 – You Try (Potato Chips)

• Given: 2\,\text{g} protein, 15\,\text{g} fat, 24\,\text{g} CHO, total 239\,\text{kcal} for 43\,\text{g}.
• %Calories from fat = [15\times9]/239\times100 \approx 56\%.
• %Calories from CHO = [24\times4]/239\times100 \approx 40\%.
• %Calories from protein ≈ 4\%.

Example 3 – Total Calories (Quaker Crispy Mini’s)

• 14\,\text{g} CHO, 1\,\text{g} protein, 3\,\text{g} fat per 20\,\text{g}.
• Total kcal = (14\times4)+(1\times4)+(3\times9)=56+4+27 = 87\,\text{kcal}.

Nutrient Density

• Concept: Nutrient content (e.g., mg calcium) per kcal of food.
• Comparative example (for calcium):
  • Skim milk: 85\,\text{kcal}, 301\,\text{mg} Ca → 301/85 \approx 3.54\,\text{mg Ca kcal}^{-1}.
  • Ice cream: 350\,\text{kcal}, 173\,\text{mg} Ca → 173/350 \approx 0.49\,\text{mg Ca kcal}^{-1}.
• Milk is ~7 times more calcium-dense than ice cream.
• Application: Favour high-density foods to meet micronutrient needs without excessive calories.

Principles of Healthy Diets

• Adequacy: Supplies all essential nutrients, fibre, and energy.
• Balance: Correct proportion among food groups and nutrients (e.g., protein vs carbohydrate).
• Calorie control: Energy intake matches expenditure to support healthy body weight.
• Moderation: Limits excess of fat (esp. saturated & trans), added sugar, sodium, alcohol, contaminants.
• Variety: Diverse foods across and within groups to reduce deficiency/toxicity risks.
• These five principles synergize—e.g., variety aids adequacy; moderation supports calorie control.

Factors Influencing Food Choices

• Availability & convenience (seasonality, geographic access, time constraints).
• Cost & economic status.
• Habit & personal preference (taste, texture, familiarity).
• Genetic influences (e.g., sensitivity to bitter compounds).
• Emotional associations (comfort foods, stress eating).
• Social and cultural norms (religion, celebrations, peer pressure).
• Advertising & media exposure.
• Health motivations (weight management, disease treatment/prevention).
• Ethical / ecological concerns (veganism, sustainability, fair trade).

Nutrition Research Methodologies

Study Designs (Fig 1-4)

• Case studies: In-depth on individuals; generate hypotheses, not generalizable.
• Epidemiological studies:
  • Cross-sectional, case–control, cohort; observe large populations; identify correlations.
• Intervention studies (Randomized Controlled Trials, RCTs): Manipulate variable in population; can establish causation if designed well.
• Laboratory studies: Cell or animal models under controlled conditions; probe mechanisms.
• Methodological rigor includes randomization, control groups, blinding, adequate sample size, appropriate statistics.

Hierarchy of Evidence (high → low)

1. Systematic reviews & meta-analyses.
2. Randomized controlled trials.
3. Cohort studies.
4. Case–control studies.
5. Cross-sectional studies.
6. Case reports/series.
7. Animal & in-vitro studies* (inform mechanisms; limited human applicability).

• Practical takeaway: Base clinical guidelines on the highest level available; single mouse study is insufficient for public recommendation.

Replication & Media Literacy

• Single studies must be replicated before acceptance.
• Media may oversimplify or sensationalize findings (“super-foods,” “toxic” nutrients).
• Consumers should look for consensus statements (e.g., WHO, Dietitians of Canada) and systematic reviews.

Identifying Reliable Nutrition Information

• Credible sources list (Table C1-2): Peer-reviewed journals, government agencies, professional organizations.
• Evaluate websites (Table C1-3): Check domain (.gov, .edu), author credentials, citations, date, conflict of interest.
• Earmarks of Quackery (Fig C1-1):
  • Promise quick, dramatic, or "miracle" results.
  • Use of sensational wording ("secret", "breakthrough") and testimonials.
  • Demonize whole foods or endorse megadoses.
  • Lack of peer-review or misuse of scientific terms.
• Ethical concern: Nutrition misinformation can lead to nutrient deficiencies, wasted resources, and harm (e.g., herbal–drug interactions).

Professional Credentials and Titles

Nutritionist

• Term unregulated in many jurisdictions.
• May possess university degree, short certification, or none at all.
• Competency and accuracy vary widely—buyer beware.

Dietitian (Registered Dietitian, RD)

• Legally protected title; governed by provincial regulatory bodies (e.g., College of Dietitians of Manitoba).
• Requirements:
  • Accredited 4-year undergraduate degree in nutrition/dietetics.
  • 8\text{–}12-month supervised practicum (clinical, community, food-service rotations).
  • Successful completion of Canadian Dietetic Registration Exam (CDRE).
  • Continuing professional development to maintain licence.
• Optional professional membership (Dietitians of Canada) for networking and resources.
• Practical implication: RDs are accountable to a code of ethics and standards of practice—key for evidence-based counselling.

Integrative Connections & Take-Home Messages

• Nutrition intersects with genetics, psychology, economics, and public policy—multidisciplinary approach enhances effectiveness of health interventions.
• For disease prevention, emphasize dietary patterns (e.g., DASH, Mediterranean) rather than isolated nutrients.
• Understanding energy density, nutrient density, and portion sizing empowers individuals to self-monitor intake.
• Critical appraisal skills (hierarchy of evidence, quackery checks) are essential in the information age.
• Seek regulated professionals (RD) for individualized guidance, especially in clinical conditions (allergies, renal disease, diabetes).