What is the effect of thyroid hormones on basal metabolic rate and related processes?

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

Answer: (A)

Thyroid hormones raise resting energy use across many tissues. They increase transcription of enzymes involved in carbohydrate, fat, and protein metabolism, boost mitochondrial activity, and upregulate Na+/K+-ATPase, all of which raise ATP turnover. That higher energy turnover requires more oxygen and substrates, so basal metabolic rate climbs. The extra energy is released as heat, causing increased heat production and overall energy expenditure—even at rest. So the best description is that thyroid hormones increase basal metabolic rate, heat production, and energy expenditure. Clinically, this explains why excess thyroid hormone leads to weight loss and heat intolerance, while deficiency lowers metabolism and energy.