Energy Balance, Metabolism and Weight Management

• Energy balance and weight management are key topics

Human Metabolism

• It represents the sum total of all physical and chemical changes within the body
• Anabolism involves the building of metabolism, for example, amino acids forming protein
• Catabolism involves the degradation of metabolism, for example, glycogen breaking down into glucose

Energy Expenditure

• Total energy expenditure (TEE) includes basal metabolism, activity, food processing, new tissue deposition, exercise, and daily activities
• Energy decreases on a diet
• Basal Metabolic Rate (BMR) is the rate of energy expenditure under resting conditions, accounting for 60-75% of total energy expenditure
• Factors that influence BMR include temperature, hormones, diet, energy intake, and body composition
• Resting Metabolic Rate (RMR) or Resting Energy Expenditure (REE) is > BMR by 10-20%
• Energy is expended due to daily activities and digestion/absorption of food, known as the thermic effect of food
• Animal-based protein is part of this process

Resting Energy Expenditure (REE)

• Can be estimated by 1 kcal/kg of weight per hour
• It is greatest at birth and progressively slows with age
• Body composition affects REE

Factors Affecting REE

• Include the amount of metabolically active tissue possessed
• Age, sex, natural hormonal activity, body size and surface area, as well as body composition

Energy Expenditure Components

• This includes non-exercise activity thermogenesis (NEAT)
• NEAT is the energy expended for activities other than sleeping, eating, or sports-like exercise
• The thermic effect of food (TEF) is the energy required for digestion, absorption, metabolism, and nutrient storage
• TEF accounts for approximately 10% of daily energy intake, with protein having a greater effect than carbs or fat

Stored Energy

• Glycogen: Stored in the liver and muscle, providing 1,400 kcal
• Glucose or free fatty acids: Stored in body fluids, providing 100 kcal
• Triglyceride: Stored in adipose tissue, providing 115,000 kcal
• Protein: Stored in muscle, providing 25,000 kcal

Energy Balance

• Positive energy balance: excess energy is stored as glycogen, body protein, and adipose tissue
• Negative energy balance: energy is derived from glycogen, body protein, and adipose tissue breakdown

Regulation of Energy Balance

• Set point theory: Weight remains relatively stable after growth, despite changes in energy intake or output
• Obesity genes: Genes (>300) code for proteins regulating food intake, energy expenditure, and body fat deposition
• Short-term regulation: Regulates food intake from meal to meal
• Long-term regulation: Regulates the amount of body fat

Short Term Regulation of Energy Balance

• Hunger: Internal signals stimulate one to acquire and consume food
• Satiation: The feeling of fullness determines the length of a meal
• Satiety: The feeling of fullness determines the time between meals
• Ghrelin: A hormone from the stomach stimulates food intake, rising 1-2 hours before eating and becoming dormant after eating

Long Term Regulation of Body Fat

• Leptin: A hormone produced by adipose tissue that regulates adipocyte balance and decreases energy intake
• Obese individuals can experience leptin resistance

Effects of Intermittent Fasting

• Body weight loss of 3-9%
• Body fat loss of 3-5.5kg
• Total cholesterol reduction of 5-21%
• Triglyceride reduction of 14-50%

Gluconeogenesis

• Synthesis of 1 g of glucose by gluconeogenesis using only amino acids requires the catabolism of 1.75 g of protein

Diets

• Most diets work by creating a caloric deficit