Energy and Metabolism Overview

Energy Overview

• Energy is vital for life processes and physiological functions.

First Law of Thermodynamics

• Energy cannot be created or destroyed, only transformed.

Food Energy

• Calories: The basic unit of energy; the amount of heat needed to raise the temperature of 1 gram of water by 1°C.
• Conversion: 1000 calories = 1 kilocalorie (Kcal or Cal).

Measurement of Food Energy

• Conducted using a bomb calorimeter:
  • A food sample is combusted in a sealed vessel called a bomb.
  • The heat released from combustion raises the temperature of the surrounding water.
  • The temperature change quantifies the energy content of the food.

Example Calculation of Calories

• Example: A food sample is burned in a calorimeter:
  • 5000 grams of water, initial temperature = 22°C, final temperature = 95°C.
  • Temperature change = 95 - 22 = 73°C.
  • Energy produced: 5000 grams x 73 = 365,000 calories.
  • In Kcal: 365,000/1000 = 365 Calories.

Energy Content of Macronutrients

• Fat: 9 Calories per gram.
• Carbohydrates: 4 Calories per gram.
• Protein: 4 Calories per gram.

Example Macronutrient Calculation

• A soup contains:
  • 15 g carbohydrates = 60 Calories (15 x 4).
  • 10 g protein = 40 Calories (10 x 4).
  • 5 g fat = 45 Calories (5 x 9).
  • Total: 60 + 40 + 45 = 145 Calories.

Percent Daily Values (DV) Calculation

• Example total energy intake: 2560 Calories consisting of:
  • Carbohydrates: 1600 Calories, 62.5% of total.
  • Protein: 240 Calories, 9.4% of total.
  • Fat: 720 Calories, 28.1% of total.

Recommended Daily Values

• Fat: 30%, Carbohydrates: 60%, Protein: 10% of total caloric intake.

Energy Density

• Energy density: Number of Calories per gram; lower density = healthier choices.
• Example measurements:
  • Potato Chips: 5.4 Calories/g
  • Baked Potato: 1.04 Calories/g.

Basal Metabolic Rate (BMR)

• BMR is the energy expenditure at rest, critical for understanding energy needs.
• Influenced by:
  • Age, muscle mass, gender, fasting, hormonal activity, stress, disease, environmental temperature, pregnancy, lactation.

Factors Influencing BMR

• Increases: Higher lean mass, younger age, elevated thyroid hormones, stress, male gender.
• Decreases: Lower lean mass, older age, starvation, female gender, certain medications.

BMR Measurement Criteria

• Pre-test: No food for 12 hours, adequate sleep, no activity for one hour.
• During test: Resting, comfortable room temperature, no physical activity.

Direct and Indirect Measurement of BMR

• Direct Calorimetry: Measures heat generated by the body.
• Indirect Calorimetry: Measures oxygen consumption for energy calculation.

Diet-Induced Thermogenesis (DIT)

• Energy required to digest and absorb food:
  • High for Proteins (30%), lower for fats (3%) and carbohydrates (5-15%).

Physical Activity Energy Expenditure

• Factors impact energy use: body weight, type, duration, and intensity of activities.
  • Example: 11.8 Calories/kg/hr for Boxing.

Energy Utilization During Starvation

• Glycogenolysis and gluconeogenesis maintain glucose levels initially, then switch to fat utilization (lipolysis, ketogenesis).

Ketogenic Diet

• Low carbohydrate, high fat, moderate protein.
• Originally for epilepsy treatment, lacks substantial evidence for weight loss efficacy.

Hormonal Regulation of Energy Metabolism

• Insulin: Releases after meals, promotes glycogen storage, inhibits fat breakdown.
• Glucagon: Increases energy availability by stimulating gluconeogenesis and glycogen breakdown between meals.
• Epinephrine and Cortisol: Influence energy metabolism in stress responses.

Body Composition Measurement

• Body Mass Index (BMI): Weight in Kg/height in m².
  • Underweight: <19, Healthy: 19-24.9, Overweight: 25-29.9, Obese: 30+.
• Skinfold measurements and hydrodensitometry used to assess body fat.

Energy Balance

• Positive balance: Energy input > output = weight gain.
• Negative balance: Energy output > input = weight loss.
• Neutral balance: Energy input = output.

Importance of Sleep on Food Intake

• Lack of sleep increases hunger (higher ghrelin) and decreases satiety (lower leptin).

Strategies for Healthy Weight Loss

• Gradual loss (10% over 6 months) preferred; avoid extreme diets.
• Sustainable physical activity and dietary practices recommended.