Which description accurately reflects thyroid hormones' influence on energy expenditure?

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

Answer: (B)

Thyroid hormones raise energy expenditure by boosting metabolic rate across almost all tissues. T3 and T4 increase transcription of enzymes involved in glycolysis, fatty acid oxidation, and oxidative phosphorylation, and they raise mitochondrial activity and density. This causes higher oxygen consumption and more heat production as energy is expended, so resting metabolic rate goes up and total energy expenditure increases. The description that best fits is that thyroid hormones increase basal metabolic rate, heat production, and energy expenditure. An option saying there’s no change is inconsistent with the thermogenic and metabolic effects of thyroid hormones, while one describing a decrease is opposite. Saying only energy expenditure increases misses the important rises in both basal metabolic rate and heat production.