23A07: Exam Report

Define basal metabolic rate and outline the factors that affect it (60% of marks). Outline the ways it may be measured (40% of Marks)

64% of candidates passed this question.

The first part of the question required candidates to define basal metabolic rate (BMR), identify the standardised conditions under which it is estimated and then elaborate on those conditions which affect it. Most candidates provided reasonable definitions but lost marks for not describing the standard conditions under which it is defined.

Many were able to give a comprehensive list of factors that affected BMR however lacked the additional pertinent facts required in an outline question to achieve full marks. Candidates are again referred to the glossary to understand the difference between a list and outline question.

The second part of the question pertained to the measurement of BMR which was not as well answered and understood. Overall, there was a limited ability to discuss direct and

Pv / 23A07: Define basal metabolic rate & list factors that affect (60 marks). Describe ways it can be measured (40 marks)

Definition

Basal metabolic rate = The amount of E liberated by catabolism of food per unit of time under standard conditions

  • Units = kcal/hr
  • 70kg male = 70kcal/hr

STANDARD CONDITIONS:
– At rest, but awake
– Postabsorptive state (not eaten in last 12hrs)
– Absence of strenuous exercise in the preivous 12hrs
– Air in room comfortable with all sources of excitement removed

Factors that Affect BMI

  • Age
    • ↑in actively growing (neonates BMR x 2 adult)
    • Adult BMR ↓2% per decade
  • Gender
    • M BMR > F BMR due to ↑skeletal mass
  • Body size
    • ↑lean weight = ↑BMR
  • Sleep
    • ↓BMR 10% due to ↓skeletal m. & CNS activity
  • Hormones (all ↑ BMR)
    • Thyroxine
    • Catecholamines
    • Testosterone
    • GH
  • Pregnancy
    • ↑15% in late pregnancy
  • Pathology
    • ↑BMR 15% per 1°C fever
    • Trauma, burns, malignancy → all ↑BMR
  • Nutrition
    • ↑BMR postprandially → thermogenic effect of food
    • Malnutrition/starvation → ↓BMR due to ↓tissue metabolism
  • Climate
    • ↑BMR 20% in arctic cf. tropics

Measurement

Standard Conditions

    • At rest + awake
    • 12hrs post meal
    • Supine → no muscular activity
    • Ambient temperature in thermoneutral zone
    • >1hr post exercise

Direct Calorimetry

  • Atwater chamber
  • Subject placed in insulated chamber surrounded by H2O
  • ∆ water temp proportional to metabolic rate

Indirect Calorimetry

    • Uses O2 consumption to calculate metabolic rate
    • 1L O2 = 4.82kcal E produced
    • Use douglas bag to measure O2 produced

H2O Benedict Chamber

  • Sealed chamber that replaces lost O2
  • Heat produced
  • Air from chamber taken out
  • Air cooled → the temp ↓is derived

Calometric Testing

Direct

Heat lost to atmosphere ∝ BMR

Indirect

O2 consumption