Energy Balance

Daily energy expenditure consists of three components: basal metabolic rate (BMR), diet-induced thermogenesis (DIT) and energy cost of physical activity.

	10%	Thermic effect of food
	20-30%	Activity
	60-70%	Resting metabolic rate

Thermic Effect of Food

• Energy required to digest, absorb, transport, and store food.
• Diet induced thermogenesis (DIT) is different for each nutrient based on the amount of ATP required for the initial steps of metabolism and storage.
  
  

• In healthy subjects with a mixed diet, where intake equals expenditure, DIT represents about 10% of the total amount of energy ingested over 24 hours.

Westerterp, KR (2004) Diet induced thermogenesis, Nutrition & Metabolism 2004, 1:5

• Also see Protein and Body Weight Regulation and Exchange List Calculator .

Activity

• Daily Activity
• Exercise
  • Aerobic exercise
    • Expends calories during exercise
  • Anaerobic exercise can increase metabolism for hours after exercise is finished
    • 3-14 hours: dependent upon intensity
    • HIIT study: for every calorie expended during anaerobics, 9 times as much fat (per calorie expended) was metabolized as compared to aerobic activity.
• Online calculators
  • Calorie Requirement Calculator
  • Metabolic Calculators: Walk / Run | Cycling | Stepping

Resting Metabolic Rate

• Energy expended to maintain the body during resting conditions.
• Muscle
  • Metabolic rate of muscle is about 10 to 15 kcal/kg per day, or 4.5 to 7.0 kcal/lb per day.
  • Contributes about 20% to Daily Energy Expenditure versus 5% for fat tissue (for individuals with about 20% body fat).
• Organs
  • Combined energy expenditure of the heart, lungs, kidneys, brain and liver represent about 80% of the Daily Energy Expenditure.
  • Have a metabolic rate that is 15-40 times greater than their equivalent weight of muscle and 50-100 times greater than fat tissue.
• May account a smaller proportion of the daily caloric needs for those who have regular vigorous exercise.
• Also see Calorie Requirement Calculator and Toning with Weights .

Elia M (1999). Organ and Tissue Contribution to Metabolic Weight. Energy Metabolism: Tissue Determinants and Cellular Corollaries. Kinney JM, Tucker HN, eds. Raven Press, Ltd. . New York: 61-79.

Energy Balance

• Neutral energy balance is when the calories you take in is equal to the calories expended.
  • Weight is maintained.
• Positive energy balance is when the calories you take in is greater than the calories expended.
  • Weight is gained and fat stores are increased.
  • One pound of fat contains approximately 3500 Calories.
• Negative energy balance: calories you take in is less than the calories expended.
  • Adipose, glycogen, and muscle can be used for energy to make up the caloric deficiency.
  • Ideally, weight is lost and fat stores are reduced.
• Appetite
  • Appetite is increased in proportion to energy expenditure over a broad range of exercise intensities and durations to maintain body weight.
  • However, formerly sedentary individuals show a net loss of appetite when exercise is introduced.

Titchenal, CA. 1988. Exercise and food intake: What is the relationship? Sports Medicine 6:135-45.

• The metabolism adjusts to changes in diet
  • If calories are increased
    • Thermo-genesis
      • Body heat is produced
    • Metabolism increases
    • Muscle mass may increase
  • If calories are restricted
    • Metabolism decreases
    • Muscle mass may decrease
  • A cascade of metabolic / hormonal changes allow the body to adapt