Which statement best describes the metabolic effects of thyroid hormones on energy use?

Which statement best describes the metabolic effects of thyroid hormones on energy use?

• 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 increase energy use by boosting overall cellular metabolism across many tissues. They upregulate the machinery of oxidative metabolism and mitochondrial activity, which raises the basal metabolic rate even at rest. This heightened metabolic activity generates more heat, so heat production goes up as a byproduct of burning more fuel. With the resting and ongoing energy demands increased, total energy expenditure rises as well. That combination—higher resting energy use, more heat production, and greater overall energy expenditure—best matches how thyroid hormones regulate metabolism. The other ideas would imply a slower, unchanged, or incomplete effect, which isn’t how thyroid hormones drive metabolic rate.