The organ that controls the body's metabolism is the thyroid gland. Located in the neck, the thyroid releases hormones such as thyroxine (T4) and triiodothyronine (T3), which are critical in regulating metabolic processes, including how the body uses energy. These hormones influence basal metabolic rate, protein synthesis, and overall energy levels. When the thyroid functions properly, it helps maintain balance in metabolism, impacting growth, development, and weight management. Disorders related to the thyroid, such as hypothyroidism or hyperthyroidism, can lead to significant fluctuations in metabolism and related health issues.