Nutrition Exam Study Notes

Nutrient Reference Values (NRVs) and Acceptable Macronutrient Distribution Ranges (AMDRs)

• Nutrient Reference Values (NRVs):
  • Fundamental values for nutrient intake recommendations.
• Acceptable Macronutrient Distribution Ranges (AMDRs):
  • Definition: Range of intakes for energy nutrients that provides adequate energy and nutrients to reduce the risk of chronic disease.
  • Importance: Need to know the ranges and how they differ among macronutrients.
  • Ranges:
    • Carbohydrates: 45-65%
    • Fat: 20-35%
    • Protein: 15-25%

Carbohydrates

• Simple Carbohydrates:
  • Generally monosaccharides and disaccharides.
  • Monosaccharides:
    • Glucose
    • Fructose (much sweeter due to different arrangement of atoms stimulating taste buds differently)
    • Galactose
  • Disaccharides:
    • Maltose (glucose + glucose)
    • Sucrose (glucose + fructose)
    • Lactose (glucose + galactose)
  • Chemical Formula: Generally the same for monosaccharides, but structural differences (arrangement of atoms) affect taste.
• Chemical Reactions:
  • Condensation: Links two monosaccharides together by removing a water molecule.
    • Hydrogen atom (H) from one monosaccharide and hydroxyl group (OH) from another combine to create water (H_2O).
  • Hydrolysis: Breaks a disaccharide into two monosaccharides by adding water.
    • Water provides hydrogen (H) and hydroxide (OH) to complete the monosaccharides.

Fatty Acids

• Naming:
  • Named by looking at methyl end.
• Saturation:
  • Saturated: No double bonds.
  • Unsaturated: Presence of double bonds.
    • Monounsaturated: One double bond.
    • Polyunsaturated: Two or more double bonds.
• Omega Number:
  • Refers to the position of the first double bond.
  • Omega-3: First double bond is at the third position.

Protein Digestion

• Process Overview:
  • General knowledge of macronutrient digestion (carbohydrates, proteins, lipids) is essential:
    • When digestion of each macronutrient starts and finishes.
    • How digestion differs among macronutrients.
• Protein Digestion Stages:
  • Mouth: Chewing and saliva moisten food.
  • Stomach: Hydrochloric acid denatures protein into polypeptides; pepsin breaks down proteins.
  • Small Intestine: Pancreatic enzymes and intestinal proteases break polypeptides into tripeptides, dipeptides, and amino acids for absorption.

Metabolism

• Metabolism Overview:
  • Knowledge of metabolism across key macronutrients (proteins, carbohydrates, fats) is critical.
• Fat Metabolism:
  • Fats are comprised of a glycerol backbone with three fatty acids.
  • Glycerol portion converts to pyruvate.
  • Fatty acid portion converts to acetyl CoA.
  • Fatty acids generally cannot make glucose; only glycerol can if the body requires it.
• Carbohydrate Metabolism:
  • Glucose breakdown to energy starts with glycolysis to pyruvate in the cytosol.
  • Conversion of pyruvate to acetyl CoA takes place in the mitochondria.
  • Pyruvate can convert to:
    • Lactic acid anaerobically (without oxygen).
    • Acetyl CoA aerobically (with oxygen).
• Protein Metabolism:
  • Proteins break down into amino acids.
  • Amino acids convert to:
    • Pyruvate.
    • Acetyl CoA.
    • Enter the TCA cycle directly, depending on the amino acid type.
• TCA Cycle (Tricarboxylic Acid Cycle) / Krebs Cycle and Electron Transport Chain:
  • All energy-yielding nutrients eventually enter the TCA cycle and then the electron transport chain.
  • Purpose of TCA cycle: To make ATP and energy through the electron transport chain.

Pyruvate and Acetyl CoA

• Key Conversions:
  • Glucose breaks down to pyruvate (glycolysis), which is reversible.
  • Pyruvate converts to lactate via anaerobic reaction (if quick energy is needed).
  • Lactate is recycled in the liver via the Cori cycle.
• Aerobic Energy Production:
  • Requires oxygen and takes place in the mitochondria.
  • Pyruvate converts to acetyl CoA.
  • Acetyl CoA enters the TCA cycle and then goes through the electron transport chain.
• Amino Acid Metabolism:
  • Amino acids are deaminated, producing ammonia (NH_3).
  • Ammonia goes to the liver and combines with carbon dioxide (CO2) to form urea ((NH2)_2CO).
  • Urea is excreted via the kidneys.
  • Excess protein can cause excess urea, stressing the kidneys.

Glucose Metabolism

• Process:
  • Glucose converts into pyruvate in the cytosol.
  • Pyruvate converts to lactic acid (anaerobic) or acetyl CoA (aerobic).
• Energy Production:
  • Aerobic pathways produce energy more slowly but in higher amounts.
  • Anaerobic pathways produce energy in short bursts but in smaller amounts.
  • All nutrients enter the TCA cycle and electron transport chain.
• TCA Cycle Details:
  • Starts and finishes with oxaloacetate.
  • Oxaloacetate combines with acetyl CoA to start the cycle.
  • Produces high-energy electrons that go to the electron transport chain for ATP generation.
  • Consumes oxygen and produces water and carbon dioxide.
• Electron Transport Chain:
  • Powers ATP synthesis.
  • ATP is the body's energy currency.

Hunger and Food Choices

• Interlinked Processes:
  • Hunger, satiation, and satiety are interlinked.
• Process Stages:
  • Physiological factors influence hunger.
  • Sensory influences (thought, sight, smell, sound, taste of food) lead to seeking food and starting a meal.
  • Cognitive influences (social stimulation, favorite food, time of day, abundant food) lead to continued eating.
  • Satiation: Ending the meal is triggered by stretch receptors in the stomach.
  • Satiety: Several hours later, post-absorptive influences signal the brain via nerves and hormones about nutrient availability, use, and storage.
  • As nutrients dwindle, satiety diminishes, and hunger develops again.
• Hormonal Involvement:
  • Understanding which hormones are involved, where they are released, and how they operate is important.
• Satiety vs. Satiation:
  • Satiety: Feeling of fullness and satisfaction.
  • Satiation: Communication with the brain to signal it is time to stop eating.

Energy Balance

• Balance:
  • Balance between energy intake and energy expenditure.
• Factors Affecting Food Choices:
  • Psychology, social influences, physical activity levels, environment, food availability.
• Energy Expenditure:
  • Differs for each individual.
• Energy Balance Components:
  • Basal Metabolic Rate (BMR): 50-65% of energy expenditure.
  • Thermic Effect of Food: ~10% of energy expenditure.
  • Physical Activity: Most variable part of energy expenditure.
• Energy Regulation:
  • Depends on energy in versus energy out.
• Bomb Calorimeter:
  • Measures direct calorimetry to determine energy in.
  • Reaction chamber is isolated with food and oxygen as reactants.
  • Changes in temperature and oxygen determine caloric value of food.
  • Heat generated is measured by changes in surrounding water temperature.
• Energy Out Measurement:
  • Direct: Measured in a chamber.
  • Indirect: Measured with a mask (Fitmate) by measuring oxygen consumed and carbon dioxide released.

Factors Influencing BMR

• BMR Contribution:
  • BMR constitutes 50-65% of energy expenditure.
  • Physical activity accounts for 30-50%, which can be adjusted for weight gain or loss.
• Factors Increasing BMR:
  • Growth (during growth spurt in teenage years).
  • Height (taller individuals have higher BMR).
  • Lean Body Mass (larger amount of metabolically active tissue).
  • Stress, fever, smoking, caffeine.
• Factors Decreasing BMR:
  • Age (drops by about 5% per decade after age 30).
  • Starvation (causes metabolism to drop).
  • Thyroid hormones (influence can decrease BMR).
  • Weight Gain after Quitting Stimulants:
  • Stopping smoking or caffeine consumption can lead to weight gain due to the reduction in the basal metabolic rate.

Fat Cell Metabolism

• Lipoprotein Lipase (LPL):
  • Enzyme that promotes fat storage in muscles and adipose tissues.
• LPL Activity and Obesity:
  • People with obesity generally have higher LPL activity than leaner individuals.
  • LPL removes triglycerides from the blood for storage.
  • High LPL activity makes fat storage efficient.
• Gender Differences:
  • Women: Fat cells in the breast, hips, and thighs produce abundant LPL.
  • Men: Fat cells in the abdomen produce large amounts of LPL, explaining central obesity.
• LPL After Weight Loss:
  • LPL activity can increase after weight loss, signaling the gene to express LPL.
  • This contributes to weight regain after rapid weight loss.
• Weight Set Point:
  • The body has a certain weight set point it likes to maintain.
  • If pushed beyond this point, weight regain is likely.
  • This is confirmed by research.