Energy Balance

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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.

Nutrient Fat Carbohydrate Protein Alcohol
DIT (% Energy) 0-3% 5-10% 20-30% 10-30%
Reference

Acheson KJ, 1983
Westerterp KR, 1999

  • 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

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

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


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