Nutrition Metabolism and Energy Balance I Flashcards
Nutrients Overview
Nutrients: Substances in food for growth, maintenance, and repair.
Used for:
Metabolic fuel
Cell structures & molecular synthesis
Macronutrients (bulk of food - carbohydrates, proteins, lipids)
Carbohydrates
Lipids
Proteins
Micronutrients (needed in small amounts)
Vitamins
Minerals
Water
Required nutrient: 60% of food intake by volume.
Essential vs Non-Essential Nutrients
Essential Nutrients:
Cannot be synthesized by the body or insufficiently synthesized. Diet only
Must come from the diet for health and survival.
40-50 essential nutrients (e.g., iron, vitamin C).
Deficiency can lead to diseases (e.g., iron deficiency anemia).
Non-Essential Nutrients:
Can be synthesized by the body.
Cells can convert one type of molecule into another.
Energy Value of Nutrients
Measured in kilocalories (kcal):
1 kcal = amount of heat to raise 1 kg of water by 1°C.
Caloric Content:
Carbohydrates & Proteins: 4 kcal/g
Lipids (Fats): 9 kcal/g
Calories: Energy in food, measured in kilocalories (kcal).
Carbohydrates & Proteins: 4 kcal/g, Lipids: 9 kcal/g.
Health Canada Food Guide
Representation: Guidelines shown as portions on a dinner plate
Food Groups:
Fruits
Vegetables
Grains
Protein
Dairy
Basic Principles:
Eat only what you need (eat less overall)
Focus on fruits, vegetables, and whole grains
Avoid junk food
Carbohydrates
Sources: Grains, vegetables, fruits, milk, meats
Fiber:
Insoluble (roughage in veggies)
Soluble (lowers cholesterol in fruits)
Uses:
Glucose: main fuel for cells
Excess stored as glycogen/fat
Diet: 45-65% of calories, mostly complex carbs
Lipids
Sources: Meat, dairy, oils (saturated, unsaturated, trans fats), eggs
Essential fatty acids: Omega-6 (linoleic), Omega-3 (linolenic)
Body Uses:
Energy storage, insulation, cell membranes
Cholesterol: stabilizes membranes, makes bile salts
Diet: 20-35% of calories, limit saturated fats to <10%
Types of Fats
Saturated: No double bonds, solid at room temp.
Sources: Beef, butter, coconut oil
Trans: Double bonds in trans config, semi-solid.
Sources: Margarine, pies
Monounsaturated: One double bond, liquid at room temp.
Sources: Olive oil, peanut oil
Polyunsaturated: Multiple double bonds, liquid.
Sources: Soybean oil, fatty fish
Metabolism & Fats
Triglycerides: Main energy source, stored long-term.
Saturated Fats: No double bonds, solid at room temp (e.g., animal fats).
Unsaturated Fats: Double bonds, liquid at room temp (e.g., seeds, nuts).
Trans Fats: Harmful, raise bad cholesterol, increase heart disease risk.
Cholesterol: Stabilizes membranes, mainly produced by the liver.
LIPIDS
Energy: High energy content, mostly carbon and hydrogen.
Sources:
Saturated fats: Animal fats, dairy, coconut oil.
Unsaturated fats: Seeds, nuts, olive oil.
Trans fats: Hydrogenated oils (e.g., margarine).
Cholesterol: Egg yolk, meats, shellfish.
Essential fatty acids:
Omega-6 (linoleic acid) and Omega-3 (linolenic acid).
Found in vegetable oils.
Functions:
Protection, insulation, fuel storage (adipose tissue).
Essential for cell membranes and myelin sheaths (phospholipids).
Helps absorb fat-soluble
vitamins.
Dietary Requirements:
Fats: 20–35% of daily calories.
Limit saturated fats to 10%.
Cholesterol is produced by the liver and not necessary in the diet.
Proteins
Structure: 3D chains of amino acids (20 total, 9 essential).
Sources:
Complete proteins: Animal products (eggs, milk, meat), soybeans.
Incomplete proteins: Legumes, nuts, grains (combine for complete profile).
Uses:
Structural: Keratin (skin), collagen (connective tissue), muscle proteins.
Functional: Enzymes, hormones.
Factors for protein use:
All-or-none rule
Adequate calorie intake
Hormonal controls (e.g., growth hormone promotes protein synthesis).
Essential for growth: Higher essential amino acid needs in children.
Proteins
Complete Proteins: Contain all 9 essential amino acids (e.g., animal products).
Incomplete Proteins: Need to combine foods (e.g., legumes + grains) for all essential amino acids.
Amino Acids: Liver can convert essential to non-essential.
Children need more protein for growth.
Key Points:
All-or-None: All essential amino acids needed for protein synthesis.
Vitamin K: Vital for blood clotting.
Nitrogen Balance
Positive: protein Synthesis > Breakdown (growth, repair).
Negative: Breakdown > Synthesis (stress, starvation).
Protein Need: 0.8g per kg body weight daily.
Vitamins
Water-soluble: B, C (supporting energy production, amino acid and nucleic acid synthesis, collagen formation, and antioxidant protection).
Fat-soluble: A (pigments, tissues), D (absorb Ca + P), E (antioxidant), K (blood clotting).
Antioxidants: A, C, E, selenium neutralize free radicals.
Sources: No single food provides all vitamins.
Minerals
Major: Ca, P, K, Na, Cl, Mg.
Trace: Iron, iodine.
Function: Strengthen bones, help blood, support body processes.
Metabolism
Sum of all biochemical reactions in the body.
Involves both anabolism (building) and catabolism (breaking down).
Even at rest, energy is used for essential activities like breathing and nutrient absorption.
Anabolism
Builds larger molecules from smaller ones (e.g., protein synthesis from amino acids).
Catabolism
Breaks down complex structures into simpler ones (e.g., hydrolysis of proteins into amino acids).
Three Stages of Metabolism or Nutrient Absorption
Stage 1 (GI Tract):
Nutrients are digested and absorbed into the blood.
Stage 2 (Tissue Cells):
Anabolism builds molecules; catabolism breaks them down (e.g., glycolysis).
Stage 3 (Cellular Respiration, Mitochondria):
Nutrients are further broken down to produce ATP, CO2, and water via the citric acid cycle and oxidative phosphorylation.
See diagram
Cellular Respiration
Goal: Break down food to capture energy in ATP.
Key Reactions:
Glycolysis
Citric Acid (Krebs) Cycle
Oxidative Phosphorylation
Oxidation-Reduction (Redox) Reactions
Oxidation: Loss of electrons (or H), releases energy.
Reduction: Gain of electrons, stores energy.
Coupled Reactions: One substance loses, another gains electrons.
Coenzymes
NAD+ → NADH (electron & hydrogen carrier).
FAD → FADH₂ (electron & hydrogen carrier).
ATP Production
Substrate-level Phosphorylation: Direct transfer of phosphate to ADP (in glycolysis and Krebs).
Oxidative Phosphorylation:
ETC: Pumps H⁺ across the membrane.
Chemiosmosis: Uses H⁺ flow to make ATP.
ATP Yield
Glycolysis: 2 ATP (net).
Krebs Cycle & ETC: ~34 ATP.
Oxidation of Glucose/Glucose Metabolism:
Glucose → Glucose-6-phosphate (trapped in the cell).
Complete breakdown needs:
Glycolysis (anaerobic)
Krebs Cycle
ETC & Oxidative Phosphorylation
Overall Reaction:
C₆H₁₂O₆ + 6O₂ → 6H₂O + 6CO₂ + 30 ATP + Heat
- Glycolysis
Location: Cytosol (no O₂ needed).
Glucose (6C) → 2 Pyruvic acids (3C).
3 Phases:
Activation: Glucose → fructose-1,6-bisphosphate.
Cleavage: Split into 2 three-carbon molecules.
Oxidation & ATP: NADH is produced, phosphate groups added, ATP formed.
NAD+ Regeneration:
With O₂: NADH donates electrons to ETC.
Without O₂: NADH reduces pyruvic acid to lactic acid.
End Products:
2 Pyruvic acids
2 NADH + H⁺
Net gain: 2 ATP
- Citric Acid Cycle (Krebs Cycle)
Location: Mitochondrial matrix.
Key Steps:
a. Decarboxylation: Pyruvic acid → CO₂.
b. Oxidation: Acetic acid formed, NADH produced.
c. Acetyl CoA: Acetic acid + CoA → Acetyl CoA.
Acetyl CoA combines with oxaloacetate → citric acid.
Produces NADH, FADH₂, CO₂, and ATP.
End Products (per glucose):
6 CO₂, 8 NADH + H⁺, 2 FADH₂, 2 ATP.
- Oxidative Phosphorylation
- Inner mitochondrial membrane
Phase 1: Electron Transport Chain (ETC): NADH and FADH₂ donate electrons to ETC, forming H₂O.
Phase 2: Chemiosmosis: Proton flow through ATP synthase drives ATP production (or ATP is synthesized from ADP and Pi as protons flow back into the matrix).
ETC Reaction:
Coenzyme-2H + ½ O₂ → Coenzyme + H₂O
(3) Oxidative phosphorylation steps:
NADH and FADH2 deliver electrons to complexes I and II.
Electrons move through complexes, releasing energy to pump H+ into the intermembrane space, creating a proton gradient. Coenzyme Q and cytochrome c shuttle electrons between complexes.
At complex IV, electrons combine with H+ and O2 to form water.
Note: Inhaled oxygen is necessary for receiving electrons and hydrogen ions from the electron transport chain. In cellular respiration, oxygen is the final electron acceptor in the electron transport chain (ETC). Oxygen binds with electrons and hydrogen ions to form water, allowing the ETC to continue functioning and enabling the production of ATP via oxidative phosphorylation. Without oxygen, the chain would back up, halting ATP production.
ATP synthase (complex V) uses the proton gradient to synthesize ATP as H+ flows through it, driving the conversion of ADP and Pi to ATP.
Oxidation of Glucose
Total ATP: 30 ATP (32 ATP - 2 for NADH transport)
Substrate-level phosphorylation: 4 ATP (2 from glycolysis, 2 from citric acid cycle)
Oxidative phosphorylation: 28 ATP (25 from NADH + 3 from FADH2)
Glycogenesis
Enzyme: Glycogen synthase
Location: Liver & skeletal muscle
Occurs when: Glucose > ATP need
Glycogenolysis
Enzyme: Glycogen phosphorylase
Occurs when: Blood glucose is low
Gluconeogenesis
Forming glucose from: Non-carb sources (e.g., glycerol, amino acids)
Energy Regulation
High ATP: Inhibits glucose breakdown, promotes glycogen/fat formation
Fats: 80-85% of stored energy
Lowest pH: Intermembrane space (H+ accumulation).
Highest pH: Matrix (low H+ concentration).
Lipid Metabolism:
Energy Source: Lipids provide 9 kcal/g, more than carbs (4 kcal/g).
Fat Breakdown: Fatty acids and glycerol are hydrolyzed and used for energy.
Triglycerides: Glycerol and fatty acids form triglycerides for storage.
Beta-Oxidation: Fatty acids break down into acetyl-CoA, entering the citric acid cycle.
Lipogenesis: Excess glucose and ATP convert into triglycerides for storage.
Lipolysis: Stored fats break down for energy, especially when carbs are low.
Ketogenesis: When carbs are scarce, acetyl-CoA is converted into ketones.
Protein Metabolism:
Breakdown & Replacement: Proteins are constantly broken down and replaced (~100 g/day). Excess amino acids are either oxidized for energy or stored as fat/glycogen.
Amino Acid Degradation:
1. Transamination: Amine group is transferred to a keto acid, forming glutamic acid.
2. Oxidative Deamination: Ammonia is removed from glutamic acid, forming urea, which is excreted.
3. Keto Acid Modification: Keto acids are modified to enter the citric acid cycle or be converted to glucose.
Protein Synthesis: Amino acids form proteins and are controlled by hormones. Essential amino acids must be obtained from the diet.
Metabolic States of the Body:
Catabolic-Anabolic Steady State:
Nutrients (amino acids, carbs, fats) are constantly broken down and rebuilt.
Controlled by liver, adipose tissue, and muscle.
Amino Acid Pool:
Free amino acids are used for protein synthesis, gluconeogenesis, and forming other compounds.
Replenished by diet.
Carbohydrate & Fat Pools:
Directly oxidized for energy or stored as fat.
Excess carbs and fats can be stored as fat, unlike amino acids.
Fed State (Absorptive State):
Occurs after eating (~4 hrs).
Anabolism exceeds catabolism, storing excess nutrients as fat.
Insulin promotes glucose uptake, fat storage, and protein synthesis.
Fasting State (Postabsorptive State):
Energy comes from body reserves (fat, glycogen, protein).
Glucagon promotes glycogen breakdown and lipolysis in adipose tissue to maintain blood glucose.
Sources of Blood Glucose:
Glycogenolysis (liver and muscle).
Lipolysis (glycerol used for gluconeogenesis).
Protein catabolism (amino acids converted to glucose).
Glucose Sparing:
During fasting, fatty acids are used for energy, conserving glucose for the brain.
Hormonal Control:
Glucagon increases blood glucose, promotes fat breakdown.
SNS (norepinephrine, epinephrine) aids in fat mobilization and glycogen breakdown.
