Which statement best describes the metabolic effects of thyroid hormones?

• A. Increase basal metabolic rate, heat production, and energy expenditure.
• B. Decrease basal metabolic rate, heat production, and energy expenditure.
• C. No change in basal metabolic rate, heat production, or energy expenditure.
• D. Increase energy expenditure only.

Answer: (A)

Thyroid hormones around the body boost energy metabolism across tissues. They ramp up mitochondrial activity, increase the expression of enzymes that burn fuel, and elevate the rate of cellular respiration. This acceleration creates more heat as a byproduct of the higher metabolic turnover, which translates into a higher resting energy expenditure. In other words, the hormones raise the basal metabolic rate and increase heat production, driving up overall energy expenditure. That makes the statement describing increased BMR, heat production, and energy expenditure the best description of their metabolic effects. It wouldn’t fit to say metabolism decreases or stays the same, and it’s more than just a single component of energy use.