Which hormone is primarily responsible for regulating metabolism in the body?

Thyroxine is primarily responsible for regulating metabolism in the body due to its role as a key hormone produced by the thyroid gland. It significantly influences the metabolic processes by increasing the basal metabolic rate (BMR), which is the rate at which the body expends energy at rest. Thyroxine helps to facilitate and regulate various bodily functions, including the metabolism of carbohydrates, fats, and proteins.

In the context of metabolism, thyroxine prompts cells to increase their metabolic activity. It affects how efficiently cells use energy and can influence weight management, energy levels, and overall metabolism. When thyroxine levels are optimal, the body functions efficiently, while imbalances can lead to metabolic disorders, such as hypothyroidism or hyperthyroidism.

Cortisol, although involved in metabolism particularly in response to stress, is more associated with the regulation of glucose levels and has roles in the body's stress response rather than directly enhancing metabolic rate as thyroxine does. Insulin primarily governs blood sugar levels and is crucial for carbohydrate metabolism rather than overall metabolic regulation. Testosterone is involved in muscle mass maintenance and development and has metabolic influences but is not the primary hormone responsible for regulating metabolism at a systemic level.