Energy Expenditure

Question 1

Energy Measurement

Answer 1

1 Calorie = 1,000 calories

Often labeled as kcal.

Becoming common to replace kcal with kilojoules

1 Cal = 4.184 kJ

Question 2

Metabolic Rate

Answer 2

The rate per hour that we expend calories by merely subsisting i.e. just sleeping.

Expenditure proportionally higher if awake and active.

Question 3

Total Energy Expenditure

(TEE)

Answer 3

The total of all calories expended over the course of a 24-hour day.

~ 60% of TEE is due to basal metabolism aka basal energy expenditure (BEE).

Question 4

BMR

vs

RMR

Answer 4

Basal metabolic rate (BMR) refers to a very specific set of conditions ⇒ at rest, fasted, not subject to stimuli, etc.

Not always practical to measure.

Resting metabolic rate (RMR) measured under more realistic conditions and regarded as “close enough” to BMR.

Question 5

Metabolic Rate

Determination

Answer 5

Metabolic rates can be estimated based on crude estimates or using emperical equations.

Estimated BMR for a man is 1 kcal/kg/hr and that of a woman is slightly less.

• Empirical equations are based on population averages.
  
  • Harris-Benedict equations most common
  • Uses height, weight, age, and set of constants.
  • Different equations used for men and women.
• Can be determined by measuring the oxygen consumed or carbon dioxide produced.
  
  • Factors exist that relate liters of gas respired to Calories expended
  • Normalized to Cal/hr or Cal/kg-hr

Question 6

Indirect Calorimetry

Answer 6

Amount of O₂ consumed and CO₂ produced used to estimate the number of kcal expended over time.

Used to estimate RMR or BMR.

Question 7

Respiratory Quotient

Answer 7

Ratio of CO₂/O₂​​

Determines what proportion of calories used comes from fats vs carbs.

RQ ≈ 0.85 in a typical american diet.

Typically get 50% of non-protein-derived energy from carbs and 50% from fats.

Patients with severe dyspnea/hypercapnia may benefit from burning fats d/t lower RQ.

Question 8

Protein Oxidation

Answer 8

RQ = 63/77 = 0.82

Protein oxidation is not evaluated with RQ but rather through measurement of urea excretion.

Test called urinary urea nitrogen or UUN.

Question 9

Macronutrient Caloric Content

Answer 9

• Carbohydrates
  
  • Max 4.1 Cal/g possible
  • 98% efficiency of digestion/absorption
  • Corrects to 4 Cal/g
• Fats
  
  • Max 9.4 Cal/g
  • 95% absorbed
  • Corrects to 9 Cal/g
• Proteins
  
  • Max 5.6 Cal/g
  • Only 92% absorbed
  • Only 75% of absorbed protein catabolized to CO₂
  • Corrects to 4 Cal/g

Question 10

Weight Loss

Answer 10

1 lb of body weight translates to a deficit of ~ 3,500 Cal

Question 11

Physical Activity Ratio

(PAR)

Answer 11

PAR divided into 3 activity levels:

Light (1-1.8)

Moderate (2-4)

Heavy (>4)

Each activity level then multiplied by BMR to calculate the energy expended performing that activity.

Question 12

Metabolic Equivalent of Task

(MET)

Answer 12

Similar to PAR.

Also refers to the increase in energy expenditure relative to basal.

Question 13

Total Energy Expenditure (TEE)

Calculation

Answer 13

In healthy individuals:

• Requires
  
  • BMR/RMR
  • energy expenditure due to physical activity
  • thermic effect
    
    • amount of energy above BMR used for processing of food for use and storage
    • estimated as additional 10% added to energy expenditure

Question 14

Injury Factor

Answer 14

Sick or injured patients enter a hypercatabolic state.

Counterregulatory hormones rise.

(glucocorticoids, epi, norepi)

Results in increased protein breakdown, gluconeogenesis, and glycogenolysis.

Increased catabolism termed the “injury factor”

Question 15

Hospitalized Patient

TEE Calculation

Answer 15

Requires:

• BMR
• Injury factor
• Physical activity factor (PAR)
  
  • simplified to 1.20 if bed riden
  • simplified to 1.30 if allowed out of bed
• Thermic effect
  
  • if they are digesting and absorbing food