In terms of energy use, what do thyroid hormones primarily increase?

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

Answer: (C)

Thyroid hormones raise how much energy the body uses across the board. They increase basal metabolic rate, meaning more energy is burned at rest just to keep cellular processes running. This happens because they boost the production and activity of metabolic enzymes, increase mitochondrial number and function, and raise the activity of Na+/K+ ATPase, all of which drive greater ATP turnover.

That higher cellular activity also drives more heat production, a consequence of the same upregulated metabolism. As cells work harder and more efficiently, more heat is generated as a byproduct, contributing to thermogenesis.

All of this combines to elevate overall energy expenditure beyond resting metabolism. So thyroid hormones don’t just affect one aspect of energy use; they elevate basal rate, heat production, and total energy expenditure. Lower or more limited effects—such as increasing energy use alone or having no change—don’t capture the full impact of thyroid hormones on metabolic rate and heat generation.