Endocrine Weight Loss Metabolic Rate and Energy Balance 2 — Questions and Answers
Question 1: Which substrate contributes most to energy expenditure during low-intensity, steady-state aerobic exercise?
- Protein
- Fat (Correct answer)
- Carbohydrate
- Ketone bodies
Correct answer: Fat
During low-intensity aerobic exercise (below ~60% VO2max), fat oxidation is the predominant energy source.
Question 2: The first law of thermodynamics applied to weight management states that:
- Weight is determined solely by hormonal balance
- Fat cells can only expand, never contract
- Energy balance equals energy intake minus energy expenditure (Correct answer)
- Carbohydrate always converts to fat regardless of total calories
Correct answer: Energy balance equals energy intake minus energy expenditure
The first law of thermodynamics dictates that energy cannot be created or destroyed; weight change reflects the net difference between energy intake and total energy expenditure.
Question 3: Which of the following factors most significantly reduces resting metabolic rate in older adults?
- Increased cortisol levels
- Loss of skeletal muscle mass (sarcopenia) (Correct answer)
- Higher fat mass percentage
- Decreased growth hormone secretion
Correct answer: Loss of skeletal muscle mass (sarcopenia)
Sarcopenia (age-related skeletal muscle loss) is the primary driver of declining resting metabolic rate in older adults because muscle is metabolically active tissue.
Question 4: Brown adipose tissue (BAT) contributes to energy expenditure primarily through:
- Lipogenesis stimulated by insulin
- Uncoupling of oxidative phosphorylation via UCP-1 (Correct answer)
- Glucagon-stimulated glycogenolysis
- Leptin-mediated appetite suppression
Correct answer: Uncoupling of oxidative phosphorylation via UCP-1
BAT generates heat by uncoupling the proton gradient in the mitochondrial inner membrane from ATP synthesis via uncoupling protein-1 (UCP-1), dissipating energy as heat.
Question 5: A caloric deficit of approximately how many kilocalories is traditionally considered necessary to lose one pound of body fat?
- 1,500 kcal
- 2,000 kcal
- 3,500 kcal (Correct answer)
- 5,000 kcal
Correct answer: 3,500 kcal
The widely used estimate is that a cumulative deficit of approximately 3,500 kcal corresponds to one pound of fat loss, though individual variation exists.
Question 6: Which clinical measurement tool provides the most accurate assessment of total body fat mass?
- Body mass index (BMI)
- Waist circumference
- Dual-energy X-ray absorptiometry (DXA) (Correct answer)
- Bioelectrical impedance analysis (BIA)
Correct answer: Dual-energy X-ray absorptiometry (DXA)
DXA is considered the clinical gold standard for measuring body composition, including fat mass, lean mass, and bone mineral density.
Endocrine Weight Loss Metabolic Rate and Energy Balance 2
Which substrate contributes most to energy expenditure during low-intensity, steady-state aerobic exercise?