Science of Nutrition

Key Concepts and Definitions

This section introduces the foundational terminology and concepts in nutrition, providing a basis for understanding the science and its application to health.

• Nutrition: The science of how food nourishes the body and influences health.

• Nutrient: A chemical substance in food that supports growth, maintenance, and repair of body tissues.

• Essential Nutrients: Nutrients that must be obtained from the diet because the body cannot make them in sufficient quantities.

• Non-Essential Nutrients: Nutrients that the body can synthesize in adequate amounts.

• Conditionally Essential Nutrients: Nutrients that are normally non-essential but become essential under certain conditions (e.g., illness).

• Calorie: A unit of energy; specifically, the amount of heat needed to raise the temperature of 1 gram of water by 1°C.

• Food Energy Values: Carbohydrates and protein provide 4 kcal/g, fat provides 9 kcal/g, and alcohol provides 7 kcal/g.

Example: If a food contains 10g of fat, it provides kcal from fat.

Characteristics of a Healthy Diet

• Adequacy: Provides sufficient energy and essential nutrients.

• Balance: Appropriate proportions of nutrients and food groups.

• Calorie Control: Managing energy intake to maintain a healthy weight.

• Moderation: Avoiding excesses of unhealthy components.

• Variety: Including diverse foods to ensure nutrient adequacy.

Factors Influencing Food Choices

• Taste and preferences

• Cultural and social factors

• Convenience and cost

• Health and nutrition knowledge

Nutrient Density

• Nutrient-Dense Foods: Foods that provide substantial nutrients with relatively few calories (e.g., vegetables, fruits).

• Energy-Dense Foods: Foods high in calories but low in nutrients (e.g., sugary snacks).

Types of Research Designs in Nutrition

• Case Studies: Detailed observations of individuals.

• Epidemiological Studies: Examine patterns in populations.

• Intervention Studies: Controlled experiments with treatment and control groups.

• Laboratory Studies: Conducted under controlled conditions, often with animals or cells.

Valid Nutrition Information vs. Quackery

• Reliable sources: Peer-reviewed journals, registered dietitians, government agencies.

• Red flags for quackery: Promises of quick fixes, lack of scientific evidence, testimonials instead of data.

Tools for Healthful Eating

Food Intake Analysis Methods

• 24-Hour Recall: Quick, but may not represent usual intake.

• Food Frequency Questionnaire: Assesses usual intake over time, but relies on memory.

• Food Diary: Detailed, but may alter eating behavior.

• Weighed Food Record: Most accurate, but time-consuming.

Dietary Reference Intakes (DRIs)

• RDA (Recommended Dietary Allowance): Average daily intake level sufficient for most healthy individuals.

• EAR (Estimated Average Requirement): Intake level estimated to meet the needs of half the healthy individuals.

• AI (Adequate Intake): Used when RDA cannot be determined; based on observed intakes.

• UL (Tolerable Upper Intake Level): Maximum daily intake unlikely to cause adverse health effects.

• AMDR (Acceptable Macronutrient Distribution Range): Range of intake for energy-yielding nutrients.

Canada’s Food Guide (CFG)

• Promotes balanced meals using the Eat Well Plate: half vegetables/fruits, one-quarter whole grains, one-quarter protein foods.

• Key nutrients: Vitamins, minerals, protein, fiber.

• Healthy eating habits: Mindful eating, cooking more often, enjoying meals with others.

Food Labelling in Canada

• Nutrition Facts label: Lists calories, macronutrients, and key micronutrients.

• Nutrient content claims: e.g., "low fat," "high fiber."

• Diet-related health claims: e.g., "A healthy diet low in saturated and trans fat may reduce the risk of heart disease."

Phytochemicals and Functional Foods

• Phytochemicals: Non-nutrient compounds in plants with health benefits (e.g., flavonoids in berries).

• Functional Foods: Foods that provide health benefits beyond basic nutrition (e.g., probiotic yogurt).

The Human Body & Digestion

Levels of Organization

• Cells → Tissues → Organs → Organ Systems → Organism

Nutrient Transport

• Blood and lymphatic systems transport nutrients to cells.

Role of Hormones and Nervous System

• Hormones regulate hunger, digestion, and metabolism (e.g., insulin, glucagon).

• Nervous system coordinates digestive processes.

"Fight, Flight, Freeze" Reaction

• Body's acute stress response, involving adrenaline and cortisol release.

Taste Sensations

• Sweet, sour, salty, bitter, umami.

Digestive System Overview

• Mouth: Mechanical and chemical digestion begins.

• Stomach: Protein digestion starts; acid and enzymes involved.

• Small intestine: Major site of digestion and absorption.

• Large intestine: Water and mineral absorption; waste formation.

Common Digestive Problems

• Heartburn, gas, diarrhea, constipation.

• Strategies: Dietary changes, hydration, physical activity.

Alcohol in Nutrition

• Standard drink sizes: 13.6g pure alcohol in Canada.

• Digestion: Absorbed in stomach and small intestine; metabolized in liver.

• Potential benefits: Moderate intake may reduce heart disease risk.

• Negatives: Addiction, liver disease, increased cancer risk.

Carbohydrates

Types and Sources

• Simple Carbohydrates: Monosaccharides (glucose, fructose) and disaccharides (sucrose, lactose).

• Complex Carbohydrates: Polysaccharides (starch, fiber, glycogen).

• Sources: Grains, fruits, vegetables, legumes.

Fiber

• Soluble Fiber: Dissolves in water; helps lower cholesterol (e.g., oats, beans).

• Insoluble Fiber: Adds bulk to stool; promotes regularity (e.g., whole grains, vegetables).

Carbohydrate Recommendations

• AMDR: 45-65% of total energy from carbohydrates.

Refined, Enriched, and Whole-Grain

• Refined: Processed to remove bran and germ.

• Enriched: Nutrients added back after processing.

• Whole-Grain: Contains all parts of the grain kernel.

Carbohydrate Digestion and Health

• Digestion: Begins in mouth, completed in small intestine.

• Lactose intolerance vs. milk allergy: Enzyme deficiency vs. immune response.

• Hyperglycemia (high blood sugar) vs. hypoglycemia (low blood sugar).

• Glycemic Index: Ranks foods by effect on blood glucose.

Diabetes

• Types: Type 1 (autoimmune), Type 2 (insulin resistance), gestational.

• Risk factors: Genetics, obesity, inactivity.

• Management: Diet, exercise, medication.

Sugar and Sweeteners

• Role of sugar in health: Excess linked to obesity, dental caries.

• Sugar alcohols: Provide fewer calories, may cause GI upset.

• Artificial sweeteners: Non-nutritive, used in diet products.

Lipids

Functions and Types

• Energy storage, insulation, cell structure, hormone production.

• Saturated Fats: No double bonds; solid at room temperature (e.g., butter).

• Unsaturated Fats: One or more double bonds; liquid at room temperature (e.g., olive oil).

• Trans Fats: Artificially hydrogenated; increase CVD risk.

Fat Digestion and Absorption

• Emulsified by bile, digested by pancreatic enzymes, absorbed as fatty acids and monoglycerides.

Dietary Recommendations

• Limit saturated and trans fats; emphasize unsaturated fats.

• AMDR for fat: 20-35% of total energy.

Essential Fatty Acids

• Omega-3: Anti-inflammatory; found in fatty fish, flaxseed.

• Omega-6: Pro-inflammatory; found in vegetable oils.

Cardiovascular Disease (CVD) and Lipids

• High intake of saturated/trans fats increases CVD risk.

• Dietary cholesterol has less impact than previously thought.

• Risk factors: High LDL, low HDL, hypertension, smoking.

Fat Substitutes and Low-Fat Diets

• Artificial fats: Olestra, Simplesse.

• Low-fat diets may lack essential nutrients if not well planned.

Proteins

Structure and Synthesis

• Composed of amino acids linked by peptide bonds.

• Sequence determines function; synthesized via transcription and translation.

Digestion and Absorption

• Begins in stomach (pepsin), completed in small intestine (proteases).

Functions in the Body

• Enzymes, hormones, immune function, tissue repair, fluid balance.

Protein Quality and Dietary Sources

• Complete proteins: Contain all essential amino acids (e.g., animal products).

• Incomplete proteins: Lacking one or more essential amino acids (e.g., most plant sources).

• Mutual supplementation: Combining foods to provide all essential amino acids.

Nitrogen Balance

• Positive: Growth, pregnancy.

• Negative: Illness, malnutrition.

Protein-Energy Malnutrition

• Marasmus: Severe energy and protein deficiency.

• Kwashiorkor: Protein deficiency with adequate energy intake.

Vegetarian and Omnivorous Diets

• Vegetarian: Lower risk of chronic disease, but may lack B12, iron, zinc.

• Omnivorous: More food choices, but may be higher in saturated fat.

Vitamins

Classes and Functions

• Fat-Soluble: Vitamins A, D, E, K; stored in body fat.

• Water-Soluble: B vitamins, vitamin C; not stored, excess excreted.

Deficiency and Toxicity

• Deficiency: Inadequate intake leads to specific diseases (e.g., scurvy, rickets).

• Toxicity: Excess intake, especially of fat-soluble vitamins, can be harmful.

Vitamin Supplements

• Valid reasons: Deficiency, pregnancy, certain health conditions.

• Invalid reasons: Belief in "extra energy" or disease prevention without evidence.

• Regulation: Health Canada oversees safety and labeling.

Water and Minerals

Functions of Water

• Solvent, transport, temperature regulation, lubrication.

Water Balance and Fluid Intake

• Balance between intake and loss (urine, sweat, respiration).

• DRI: Varies by age, sex, activity, climate.

Electrolytes

• Minerals that help regulate fluid balance (e.g., sodium, potassium, chloride).

Major and Trace Minerals

• Major: Calcium, phosphorus, magnesium, sodium, potassium, chloride, sulfur.

• Trace: Iron, zinc, copper, iodine, selenium, etc.

Osteoporosis and Bone Health

• Osteoporosis: Weak, brittle bones due to low bone mass.

• Peak bone mass: Maximum bone density achieved, usually by age 30.

• Cortical vs. trabecular bone: Dense outer layer vs. spongy inner structure.

Alcohol

Energy and Metabolism

• Provides 7 kcal/g; not a nutrient.

• Metabolized primarily in the liver.

Health Effects

• Moderate intake: Possible cardiovascular benefits.

• Excess: Liver disease, addiction, increased cancer risk.

Energy Balance: Body Weight, Obesity, & Eating Disorders

Energy Balance and Expenditure

• Energy balance: Calories in vs. calories out.

• Components: Basal metabolic rate (BMR), physical activity, thermic effect of food.

Equation:

Body Mass Index (BMI)

• Calculation:

• Categories: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese (≥30)

• Limitations: Does not account for muscle mass, age, ethnicity.

Body Composition Assessment

• Methods: Skinfolds, bioelectrical impedance, DEXA, underwater weighing.

Hunger, Appetite, and Satiety

• Hunger: Physiological need for food.

• Appetite: Psychological desire to eat.

• Satiety: Feeling of fullness after eating.

• Leptin: Hormone regulating satiety and energy balance.

Weight Management Approaches

• Weight normative: Focus on weight loss.

• Weight inclusive: Focus on health at any size.

• Unsound approaches: Fad diets, extreme restriction.

Eating Disorders

• Anorexia nervosa, bulimia nervosa, binge eating disorder.

• Characteristics: Distorted body image, unhealthy eating behaviors.

• Complications: Malnutrition, electrolyte imbalance, psychological distress.

Nutrition & Fitness

Physical Activity and Nutrition

• Benefits: Improved cardiovascular health, muscle strength, mental well-being.

• Recommendations: At least 150 minutes of moderate-intensity activity per week.

Fuel Use During Activity

• At rest: Fat is primary fuel.

• Early activity: Glycogen (carbohydrate) used.

• Prolonged activity: Increased fat use as glycogen depletes.

Dietary Strategies for Athletes

• Maintain glucose: Carbohydrate loading, regular intake during endurance events.

• Protein: Supports muscle repair and growth.

• Fat: Should not be excessively restricted.

• Vitamins/minerals: Usually met with balanced diet; supplements rarely needed.

• Hydration: Essential for performance and safety.

• Sports drinks: Useful for prolonged, intense activity.

• Ergogenic aids: Some may help (e.g., caffeine), others are unsafe or unproven.

Food Safety & Regulation

Food Safety Principles

• Preventing foodborne illness: Proper cooking, storage, hygiene.

• Regulation: Government agencies set standards for food safety and labeling.

Food Insecurity in the US and the World

Food Insecurity

• Lack of consistent access to enough food for an active, healthy life.

• Causes: Poverty, conflict, climate change, inequality.

• Consequences: Malnutrition, poor health, impaired development.

Nutrition: Pregnancy Through Infancy

Nutrition During Pregnancy and Infancy

• Increased nutrient needs for growth and development.

• Key nutrients: Folate, iron, calcium, protein.

• Breastfeeding: Recommended for first 6 months; provides ideal nutrition.

Nutrition: Toddlers to Late Adulthood

Nutrition Across the Lifespan

• Changing nutrient needs with age: Growth, maintenance, prevention of chronic disease.

• Common concerns: Iron deficiency in children, bone health in older adults.

• Strategies: Balanced diet, physical activity, regular health monitoring.