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.