Understanding Energy Balance and Influences

Aug 19, 2024

Lecture on Energy Balance

Overview of Energy Balance

  • Energy Balance: Occurs when caloric intake equals caloric expenditure; body weight remains stable.
  • Positive Energy Balance: Energy intake > expenditure, leading to weight gain.
  • Negative Energy Balance: Energy intake < expenditure, leading to weight loss.

Components of Energy Intake and Expenditure

  • Focus on energy expenditure components as intake sources are previously covered.

Hunger and Appetite

  • Hunger: Physical need for food, triggered by physiological signals (empty stomach, hormones).
  • Appetite: Desire influenced by external cues (smell, sight, taste).
  • Satiation and Satiety: Feelings of fullness post-eating.

Steps and Influences in Eating

  1. Physiological Influences: Empty stomach, lack of nutrients, triggers hunger.
  2. Sensory Influences: Smell and sight of food increase desire to eat.
  3. Cognitive Influences: Social situations, time of day, availability influence eating.
  4. Post-Ingestive Influences: Stretch receptors and nutrients signal fullness.
  5. Post-Absorptive Influences: Nutrient levels in blood influence satiety.

Hormonal Regulation

  • Leptin: Produced by fat cells, suppresses appetite. Issues with leptin resistance in obesity.
  • Ghrelin: Produced by stomach, triggers hunger. Levels vary with body composition.

Energy Expenditure Components

  1. Basal Metabolic Rate (BMR): 50-70% of expenditure, basic life functions.
  2. Physical Activity: 15-30% of expenditure, can increase BMR.
  3. Thermic Effect of Food (TEF): ~10% of expenditure, energy for digestion.

Factors Influencing BMR

  • Lean Body Mass: Higher mass increases BMR.
  • Gender: Males generally have higher BMR due to more lean mass.
  • Age: BMR decreases with age.
  • Energy Restriction: Severe calorie restriction slows BMR.
  • Hormones and Growth: Influence BMR during pregnancy, stress, etc.

Calculating Caloric Needs

  • Harris-Benedict Equation: Considers height, weight, gender, activity level.
  • Calories per kg Method:
    • Maintain: 25-30 kcal/kg
    • Gain: 30-35 kcal/kg
    • Lose: 20-25 kcal/kg

Weight Loss and Caloric Deficit

  • 3,500 kcal = 1 pound of fat: Reducing intake by 500 kcal/day aims to lose 1 pound/week.
  • Consideration of factors beyond caloric intake, such as exercise, for weight loss.

This lecture provides a comprehensive overview of the intricacies of energy balance, emphasizing the importance of understanding both physiological and external factors influencing energy intake and expenditure.