Metabolism Overview Quiz

Metabolism

• Chemical reactions within body cells.
• Two main types: catabolic and anabolic.

Catabolic Reactions

• Break down complex food molecules (proteins, fats, carbohydrates).
• Produce simpler molecules and energy:
  • Chemical energy (ATP): used for muscle contraction, cellular processes.
  • Heat energy: maintains body temperature.

Anabolic Reactions

• Synthesize complex molecules from smaller ones.
  • Proteins from amino acids.
  • Fats from fatty acids.
  • Glucose from lactic acid.

Metabolic Rate

• Amount of heat released per hour during chemical reactions.
• Measured in calories (kilocalories or Calories): heat to raise 1 kg water by 1°C.
• Energy equivalent of O2:
  • Carbohydrates: 5 calories/liter O2
  • Fat: 4.7 calories/liter O2
  • Protein: 4.5 calories/liter O2
  • Mixed food: 4.8 calories/liter O2

Measuring Metabolic Rate

• Direct Calorimetry: measures heat lost by a subject in a calorimeter.
• Indirect Calorimetry: calculates heat produced from O2 consumption (MR = O2 utilized (liters/hour) × 4.8).

Energy Balance

• In healthy adults, energy intake equals energy output.
• Energy output includes:
  • Internal work: metabolic functions, digestion, temperature regulation.
  • External work: physical activity.

Specific Dynamic Action of Food (SDA) / Thermal Effect of Food (TEF)

• Energy used to digest, absorb, and metabolize food.
• Contributes to daily calorie expenditure.
• Starts one hour after eating, lasts 4-12 hours.
• Factors affecting TEF: age (decreases with age), physical activity (increases TEF), meal size, composition, frequency, processing, and external temperature.
• Proteins have the highest TEF.
• TEF is directly proportional to food intake.
• TEF decreases at low temperatures and increases at high temperatures.

Total Energy Expenditure

• Includes internal and external work plus TEF.