Kaplan Nursing Entrance Exam Practice 2026 – Comprehensive Prep

The hormone that primarily controls the rate of metabolism for fats, proteins, and carbohydrates is thyroxine. This hormone, produced by the thyroid gland, plays a crucial role in regulating the body's basal metabolic rate, which determines how quickly the body uses energy and metabolizes nutrients. Thyroxine influences many bodily functions, including heart rate, digestion, and muscle function, by increasing the metabolic rate at which the body converts food into energy.

While other hormones mentioned, such as insulin and glucagon, have important roles in carbohydrate metabolism and blood sugar regulation, they are not the primary regulators of overall metabolic rate. Insulin primarily lowers blood sugar levels by promoting the uptake of glucose, while glucagon works to raise blood sugar levels. Cortisol, a stress hormone, also affects metabolism but is more involved in the body's response to stress rather than direct metabolic control.

Thyroxine's central role in metabolic regulation makes it the most accurate choice for this question.