What is the primary effect of increased thyroxine (T4) secretion on basal metabolic rate (BMR) and on long-term energy balance?

T4 has no measurable effect on metabolism but only changes appetite hormones such as ghrelin and leptin

T4 directly causes immediate loss of muscle mass without affecting caloric expenditure, thereby causing weight loss that is unhealthy and unrelated to energy balance

Increased T4 lowers BMR and therefore promotes weight gain by reducing resting energy expenditure

Increased T4 raises BMR, increasing background energy expenditure and tending to reduce energy storage (weight) over time if intake is unchanged